PhabricatorCursorPagedPolicyAwareQuery.php
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Created: Tue, Jul 16, 01:41

PhabricatorCursorPagedPolicyAwareQuery.php
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	<?php

	/**
	* A query class which uses cursor-based paging. This paging is much more
	* performant than offset-based paging in the presence of policy filtering.
	*
	* @task clauses Building Query Clauses
	* @task appsearch Integration with ApplicationSearch
	* @task customfield Integration with CustomField
	* @task paging Paging
	* @task order Result Ordering
	* @task edgelogic Working with Edge Logic
	* @task spaces Working with Spaces
	*/
	abstract class PhabricatorCursorPagedPolicyAwareQuery
	extends PhabricatorPolicyAwareQuery {

	private $afterID;
	private $beforeID;
	private $applicationSearchConstraints = array();
	private $internalPaging;
	private $orderVector;
	private $groupVector;
	private $builtinOrder;
	private $edgeLogicConstraints = array();
	private $edgeLogicConstraintsAreValid = false;
	private $spacePHIDs;
	private $spaceIsArchived;
	private $ngrams = array();

	protected function getPageCursors(array $page) {
	return array(
	$this->getResultCursor(head($page)),
	$this->getResultCursor(last($page)),
	);
	}

	protected function getResultCursor($object) {
	if (!is_object($object)) {
	throw new Exception(
	pht(
	'Expected object, got "%s".',
	gettype($object)));
	}

	return $object->getID();
	}

	protected function nextPage(array $page) {
	// See getPagingViewer() for a description of this flag.
	$this->internalPaging = true;

	if ($this->beforeID !== null) {
	$page = array_reverse($page, $preserve_keys = true);
	list($before, $after) = $this->getPageCursors($page);
	$this->beforeID = $before;
	} else {
	list($before, $after) = $this->getPageCursors($page);
	$this->afterID = $after;
	}
	}

	final public function setAfterID($object_id) {
	$this->afterID = $object_id;
	return $this;
	}

	final protected function getAfterID() {
	return $this->afterID;
	}

	final public function setBeforeID($object_id) {
	$this->beforeID = $object_id;
	return $this;
	}

	final protected function getBeforeID() {
	return $this->beforeID;
	}

	protected function loadStandardPage(PhabricatorLiskDAO $table) {
	$rows = $this->loadStandardPageRows($table);
	return $table->loadAllFromArray($rows);
	}

	protected function loadStandardPageRows(PhabricatorLiskDAO $table) {
	$conn = $table->establishConnection('r');

	$rows = queryfx_all(
	$conn,
	'%Q FROM %T %Q %Q %Q %Q %Q %Q %Q',
	$this->buildSelectClause($conn),
	$table->getTableName(),
	(string)$this->getPrimaryTableAlias(),
	$this->buildJoinClause($conn),
	$this->buildWhereClause($conn),
	$this->buildGroupClause($conn),
	$this->buildHavingClause($conn),
	$this->buildOrderClause($conn),
	$this->buildLimitClause($conn));

	return $rows;
	}

	/**
	* Get the viewer for making cursor paging queries.
	*
	* NOTE: You should ONLY use this viewer to load cursor objects while
	* building paging queries.
	*
	* Cursor paging can happen in two ways. First, the user can request a page
	* like `/stuff/?after=33`, which explicitly causes paging. Otherwise, we
	* can fall back to implicit paging if we filter some results out of a
	* result list because the user can't see them and need to go fetch some more
	* results to generate a large enough result list.
	*
	* In the first case, want to use the viewer's policies to load the object.
	* This prevents an attacker from figuring out information about an object
	* they can't see by executing queries like `/stuff/?after=33&order=name`,
	* which would otherwise give them a hint about the name of the object.
	* Generally, if a user can't see an object, they can't use it to page.
	*
	* In the second case, we need to load the object whether the user can see
	* it or not, because we need to examine new results. For example, if a user
	* loads `/stuff/` and we run a query for the first 100 items that they can
	* see, but the first 100 rows in the database aren't visible, we need to
	* be able to issue a query for the next 100 results. If we can't load the
	* cursor object, we'll fail or issue the same query over and over again.
	* So, generally, internal paging must bypass policy controls.
	*
	* This method returns the appropriate viewer, based on the context in which
	* the paging is occuring.
	*
	* @return PhabricatorUser Viewer for executing paging queries.
	*/
	final protected function getPagingViewer() {
	if ($this->internalPaging) {
	return PhabricatorUser::getOmnipotentUser();
	} else {
	return $this->getViewer();
	}
	}

	final protected function buildLimitClause(AphrontDatabaseConnection $conn_r) {
	if ($this->getRawResultLimit()) {
	return qsprintf($conn_r, 'LIMIT %d', $this->getRawResultLimit());
	} else {
	return '';
	}
	}

	final protected function didLoadResults(array $results) {
	if ($this->beforeID) {
	$results = array_reverse($results, $preserve_keys = true);
	}
	return $results;
	}

	final public function executeWithCursorPager(AphrontCursorPagerView $pager) {
	$limit = $pager->getPageSize();

	$this->setLimit($limit + 1);

	if ($pager->getAfterID()) {
	$this->setAfterID($pager->getAfterID());
	} else if ($pager->getBeforeID()) {
	$this->setBeforeID($pager->getBeforeID());
	}

	$results = $this->execute();
	$count = count($results);

	$sliced_results = $pager->sliceResults($results);
	if ($sliced_results) {
	list($before, $after) = $this->getPageCursors($sliced_results);

	if ($pager->getBeforeID() \|\| ($count > $limit)) {
	$pager->setNextPageID($after);
	}

	if ($pager->getAfterID() \|\|
	($pager->getBeforeID() && ($count > $limit))) {
	$pager->setPrevPageID($before);
	}
	}

	return $sliced_results;
	}


	/**
	* Return the alias this query uses to identify the primary table.
	*
	* Some automatic query constructions may need to be qualified with a table
	* alias if the query performs joins which make column names ambiguous. If
	* this is the case, return the alias for the primary table the query
	* uses; generally the object table which has `id` and `phid` columns.
	*
	* @return string Alias for the primary table.
	*/
	protected function getPrimaryTableAlias() {
	return null;
	}

	public function newResultObject() {
	return null;
	}


	/* -( Building Query Clauses )--------------------------------------------- */


	/**
	* @task clauses
	*/
	protected function buildSelectClause(AphrontDatabaseConnection $conn) {
	$parts = $this->buildSelectClauseParts($conn);
	return $this->formatSelectClause($parts);
	}


	/**
	* @task clauses
	*/
	protected function buildSelectClauseParts(AphrontDatabaseConnection $conn) {
	$select = array();

	$alias = $this->getPrimaryTableAlias();
	if ($alias) {
	$select[] = qsprintf($conn, '%T.*', $alias);
	} else {
	$select[] = '*';
	}

	$select[] = $this->buildEdgeLogicSelectClause($conn);

	return $select;
	}


	/**
	* @task clauses
	*/
	protected function buildJoinClause(AphrontDatabaseConnection $conn) {
	$joins = $this->buildJoinClauseParts($conn);
	return $this->formatJoinClause($joins);
	}


	/**
	* @task clauses
	*/
	protected function buildJoinClauseParts(AphrontDatabaseConnection $conn) {
	$joins = array();
	$joins[] = $this->buildEdgeLogicJoinClause($conn);
	$joins[] = $this->buildApplicationSearchJoinClause($conn);
	$joins[] = $this->buildNgramsJoinClause($conn);
	return $joins;
	}


	/**
	* @task clauses
	*/
	protected function buildWhereClause(AphrontDatabaseConnection $conn) {
	$where = $this->buildWhereClauseParts($conn);
	return $this->formatWhereClause($where);
	}


	/**
	* @task clauses
	*/
	protected function buildWhereClauseParts(AphrontDatabaseConnection $conn) {
	$where = array();
	$where[] = $this->buildPagingClause($conn);
	$where[] = $this->buildEdgeLogicWhereClause($conn);
	$where[] = $this->buildSpacesWhereClause($conn);
	$where[] = $this->buildNgramsWhereClause($conn);
	return $where;
	}


	/**
	* @task clauses
	*/
	protected function buildHavingClause(AphrontDatabaseConnection $conn) {
	$having = $this->buildHavingClauseParts($conn);
	return $this->formatHavingClause($having);
	}


	/**
	* @task clauses
	*/
	protected function buildHavingClauseParts(AphrontDatabaseConnection $conn) {
	$having = array();
	$having[] = $this->buildEdgeLogicHavingClause($conn);
	return $having;
	}


	/**
	* @task clauses
	*/
	protected function buildGroupClause(AphrontDatabaseConnection $conn) {
	if (!$this->shouldGroupQueryResultRows()) {
	return '';
	}

	return qsprintf(
	$conn,
	'GROUP BY %Q',
	$this->getApplicationSearchObjectPHIDColumn());
	}


	/**
	* @task clauses
	*/
	protected function shouldGroupQueryResultRows() {
	if ($this->shouldGroupEdgeLogicResultRows()) {
	return true;
	}

	if ($this->getApplicationSearchMayJoinMultipleRows()) {
	return true;
	}

	if ($this->shouldGroupNgramResultRows()) {
	return true;
	}

	return false;
	}



	/* -( Paging )------------------------------------------------------------- */


	/**
	* @task paging
	*/
	protected function buildPagingClause(AphrontDatabaseConnection $conn) {
	$orderable = $this->getOrderableColumns();
	$vector = $this->getOrderVector();

	if ($this->beforeID !== null) {
	$cursor = $this->beforeID;
	$reversed = true;
	} else if ($this->afterID !== null) {
	$cursor = $this->afterID;
	$reversed = false;
	} else {
	// No paging is being applied to this query so we do not need to
	// construct a paging clause.
	return '';
	}

	$keys = array();
	foreach ($vector as $order) {
	$keys[] = $order->getOrderKey();
	}

	$value_map = $this->getPagingValueMap($cursor, $keys);

	$columns = array();
	foreach ($vector as $order) {
	$key = $order->getOrderKey();

	if (!array_key_exists($key, $value_map)) {
	throw new Exception(
	pht(
	'Query "%s" failed to return a value from getPagingValueMap() '.
	'for column "%s".',
	get_class($this),
	$key));
	}

	$column = $orderable[$key];
	$column['value'] = $value_map[$key];

	$columns[] = $column;
	}

	return $this->buildPagingClauseFromMultipleColumns(
	$conn,
	$columns,
	array(
	'reversed' => $reversed,
	));
	}


	/**
	* @task paging
	*/
	protected function getPagingValueMap($cursor, array $keys) {
	return array(
	'id' => $cursor,
	);
	}


	/**
	* @task paging
	*/
	protected function loadCursorObject($cursor) {
	$query = newv(get_class($this), array())
	->setViewer($this->getPagingViewer())
	->withIDs(array((int)$cursor));

	$this->willExecuteCursorQuery($query);

	$object = $query->executeOne();
	if (!$object) {
	throw new Exception(
	pht(
	'Cursor "%s" does not identify a valid object in query "%s".',
	$cursor,
	get_class($this)));
	}

	return $object;
	}


	/**
	* @task paging
	*/
	protected function willExecuteCursorQuery(
	PhabricatorCursorPagedPolicyAwareQuery $query) {
	return;
	}


	/**
	* Simplifies the task of constructing a paging clause across multiple
	* columns. In the general case, this looks like:
	*
	* A > a OR (A = a AND B > b) OR (A = a AND B = b AND C > c)
	*
	* To build a clause, specify the name, type, and value of each column
	* to include:
	*
	* $this->buildPagingClauseFromMultipleColumns(
	* $conn_r,
	* array(
	* array(
	* 'table' => 't',
	* 'column' => 'title',
	* 'type' => 'string',
	* 'value' => $cursor->getTitle(),
	* 'reverse' => true,
	* ),
	* array(
	* 'table' => 't',
	* 'column' => 'id',
	* 'type' => 'int',
	* 'value' => $cursor->getID(),
	* ),
	* ),
	* array(
	* 'reversed' => $is_reversed,
	* ));
	*
	* This method will then return a composable clause for inclusion in WHERE.
	*
	* @param AphrontDatabaseConnection Connection query will execute on.
	* @param list<map> Column description dictionaries.
	* @param map Additional constuction options.
	* @return string Query clause.
	* @task paging
	*/
	final protected function buildPagingClauseFromMultipleColumns(
	AphrontDatabaseConnection $conn,
	array $columns,
	array $options) {

	foreach ($columns as $column) {
	PhutilTypeSpec::checkMap(
	$column,
	array(
	'table' => 'optional string\|null',
	'column' => 'string',
	'value' => 'wild',
	'type' => 'string',
	'reverse' => 'optional bool',
	'unique' => 'optional bool',
	'null' => 'optional string\|null',
	));
	}

	PhutilTypeSpec::checkMap(
	$options,
	array(
	'reversed' => 'optional bool',
	));

	$is_query_reversed = idx($options, 'reversed', false);

	$clauses = array();
	$accumulated = array();
	$last_key = last_key($columns);
	foreach ($columns as $key => $column) {
	$type = $column['type'];

	$null = idx($column, 'null');
	if ($column['value'] === null) {
	if ($null) {
	$value = null;
	} else {
	throw new Exception(
	pht(
	'Column "%s" has null value, but does not specify a null '.
	'behavior.',
	$key));
	}
	} else {
	switch ($type) {
	case 'int':
	$value = qsprintf($conn, '%d', $column['value']);
	break;
	case 'float':
	$value = qsprintf($conn, '%f', $column['value']);
	break;
	case 'string':
	$value = qsprintf($conn, '%s', $column['value']);
	break;
	default:
	throw new Exception(
	pht(
	'Column "%s" has unknown column type "%s".',
	$column['column'],
	$type));
	}
	}

	$is_column_reversed = idx($column, 'reverse', false);
	$reverse = ($is_query_reversed xor $is_column_reversed);

	$clause = $accumulated;

	$table_name = idx($column, 'table');
	$column_name = $column['column'];
	if ($table_name !== null) {
	$field = qsprintf($conn, '%T.%T', $table_name, $column_name);
	} else {
	$field = qsprintf($conn, '%T', $column_name);
	}

	$parts = array();
	if ($null) {
	$can_page_if_null = ($null === 'head');
	$can_page_if_nonnull = ($null === 'tail');

	if ($reverse) {
	$can_page_if_null = !$can_page_if_null;
	$can_page_if_nonnull = !$can_page_if_nonnull;
	}

	$subclause = null;
	if ($can_page_if_null && $value === null) {
	$parts[] = qsprintf(
	$conn,
	'(%Q IS NOT NULL)',
	$field);
	} else if ($can_page_if_nonnull && $value !== null) {
	$parts[] = qsprintf(
	$conn,
	'(%Q IS NULL)',
	$field);
	}
	}

	if ($value !== null) {
	$parts[] = qsprintf(
	$conn,
	'%Q %Q %Q',
	$field,
	$reverse ? '>' : '<',
	$value);
	}

	if ($parts) {
	if (count($parts) > 1) {
	$clause[] = '('.implode(') OR (', $parts).')';
	} else {
	$clause[] = head($parts);
	}
	}

	if ($clause) {
	if (count($clause) > 1) {
	$clauses[] = '('.implode(') AND (', $clause).')';
	} else {
	$clauses[] = head($clause);
	}
	}

	if ($value === null) {
	$accumulated[] = qsprintf(
	$conn,
	'%Q IS NULL',
	$field);
	} else {
	$accumulated[] = qsprintf(
	$conn,
	'%Q = %Q',
	$field,
	$value);
	}
	}

	return '('.implode(') OR (', $clauses).')';
	}


	/* -( Result Ordering )---------------------------------------------------- */


	/**
	* Select a result ordering.
	*
	* This is a high-level method which selects an ordering from a predefined
	* list of builtin orders, as provided by @{method:getBuiltinOrders}. These
	* options are user-facing and not exhaustive, but are generally convenient
	* and meaningful.
	*
	* You can also use @{method:setOrderVector} to specify a low-level ordering
	* across individual orderable columns. This offers greater control but is
	* also more involved.
	*
	* @param string Key of a builtin order supported by this query.
	* @return this
	* @task order
	*/
	public function setOrder($order) {
	$aliases = $this->getBuiltinOrderAliasMap();

	if (empty($aliases[$order])) {
	throw new Exception(
	pht(
	'Query "%s" does not support a builtin order "%s". Supported orders '.
	'are: %s.',
	get_class($this),
	$order,
	implode(', ', array_keys($aliases))));
	}

	$this->builtinOrder = $aliases[$order];
	$this->orderVector = null;

	return $this;
	}


	/**
	* Set a grouping order to apply before primary result ordering.
	*
	* This allows you to preface the query order vector with additional orders,
	* so you can effect "group by" queries while still respecting "order by".
	*
	* This is a high-level method which works alongside @{method:setOrder}. For
	* lower-level control over order vectors, use @{method:setOrderVector}.
	*
	* @param PhabricatorQueryOrderVector\|list<string> List of order keys.
	* @return this
	* @task order
	*/
	public function setGroupVector($vector) {
	$this->groupVector = $vector;
	$this->orderVector = null;

	return $this;
	}


	/**
	* Get builtin orders for this class.
	*
	* In application UIs, we want to be able to present users with a small
	* selection of meaningful order options (like "Order by Title") rather than
	* an exhaustive set of column ordering options.
	*
	* Meaningful user-facing orders are often really orders across multiple
	* columns: for example, a "title" ordering is usually implemented as a
	* "title, id" ordering under the hood.
	*
	* Builtin orders provide a mapping from convenient, understandable
	* user-facing orders to implementations.
	*
	* A builtin order should provide these keys:
	*
	* - `vector` (`list<string>`): The actual order vector to use.
	* - `name` (`string`): Human-readable order name.
	*
	* @return map<string, wild> Map from builtin order keys to specification.
	* @task order
	*/
	public function getBuiltinOrders() {
	$orders = array(
	'newest' => array(
	'vector' => array('id'),
	'name' => pht('Creation (Newest First)'),
	'aliases' => array('created'),
	),
	'oldest' => array(
	'vector' => array('-id'),
	'name' => pht('Creation (Oldest First)'),
	),
	);

	$object = $this->newResultObject();
	if ($object instanceof PhabricatorCustomFieldInterface) {
	$list = PhabricatorCustomField::getObjectFields(
	$object,
	PhabricatorCustomField::ROLE_APPLICATIONSEARCH);
	foreach ($list->getFields() as $field) {
	$index = $field->buildOrderIndex();
	if (!$index) {
	continue;
	}

	$legacy_key = 'custom:'.$field->getFieldKey();
	$modern_key = $field->getModernFieldKey();

	$orders[$modern_key] = array(
	'vector' => array($modern_key, 'id'),
	'name' => $field->getFieldName(),
	'aliases' => array($legacy_key),
	);

	$orders['-'.$modern_key] = array(
	'vector' => array('-'.$modern_key, '-id'),
	'name' => pht('%s (Reversed)', $field->getFieldName()),
	);
	}
	}

	return $orders;
	}

	public function getBuiltinOrderAliasMap() {
	$orders = $this->getBuiltinOrders();

	$map = array();
	foreach ($orders as $key => $order) {
	$keys = array();
	$keys[] = $key;
	foreach (idx($order, 'aliases', array()) as $alias) {
	$keys[] = $alias;
	}

	foreach ($keys as $alias) {
	if (isset($map[$alias])) {
	throw new Exception(
	pht(
	'Two builtin orders ("%s" and "%s") define the same key or '.
	'alias ("%s"). Each order alias and key must be unique and '.
	'identify a single order.',
	$key,
	$map[$alias],
	$alias));
	}
	$map[$alias] = $key;
	}
	}

	return $map;
	}


	/**
	* Set a low-level column ordering.
	*
	* This is a low-level method which offers granular control over column
	* ordering. In most cases, applications can more easily use
	* @{method:setOrder} to choose a high-level builtin order.
	*
	* To set an order vector, specify a list of order keys as provided by
	* @{method:getOrderableColumns}.
	*
	* @param PhabricatorQueryOrderVector\|list<string> List of order keys.
	* @return this
	* @task order
	*/
	public function setOrderVector($vector) {
	$vector = PhabricatorQueryOrderVector::newFromVector($vector);

	$orderable = $this->getOrderableColumns();

	// Make sure that all the components identify valid columns.
	$unique = array();
	foreach ($vector as $order) {
	$key = $order->getOrderKey();
	if (empty($orderable[$key])) {
	$valid = implode(', ', array_keys($orderable));
	throw new Exception(
	pht(
	'This query ("%s") does not support sorting by order key "%s". '.
	'Supported orders are: %s.',
	get_class($this),
	$key,
	$valid));
	}

	$unique[$key] = idx($orderable[$key], 'unique', false);
	}

	// Make sure that the last column is unique so that this is a strong
	// ordering which can be used for paging.
	$last = last($unique);
	if ($last !== true) {
	throw new Exception(
	pht(
	'Order vector "%s" is invalid: the last column in an order must '.
	'be a column with unique values, but "%s" is not unique.',
	$vector->getAsString(),
	last_key($unique)));
	}

	// Make sure that other columns are not unique; an ordering like "id, name"
	// does not make sense because only "id" can ever have an effect.
	array_pop($unique);
	foreach ($unique as $key => $is_unique) {
	if ($is_unique) {
	throw new Exception(
	pht(
	'Order vector "%s" is invalid: only the last column in an order '.
	'may be unique, but "%s" is a unique column and not the last '.
	'column in the order.',
	$vector->getAsString(),
	$key));
	}
	}

	$this->orderVector = $vector;
	return $this;
	}


	/**
	* Get the effective order vector.
	*
	* @return PhabricatorQueryOrderVector Effective vector.
	* @task order
	*/
	protected function getOrderVector() {
	if (!$this->orderVector) {
	if ($this->builtinOrder !== null) {
	$builtin_order = idx($this->getBuiltinOrders(), $this->builtinOrder);
	$vector = $builtin_order['vector'];
	} else {
	$vector = $this->getDefaultOrderVector();
	}

	if ($this->groupVector) {
	$group = PhabricatorQueryOrderVector::newFromVector($this->groupVector);
	$group->appendVector($vector);
	$vector = $group;
	}

	$vector = PhabricatorQueryOrderVector::newFromVector($vector);

	// We call setOrderVector() here to apply checks to the default vector.
	// This catches any errors in the implementation.
	$this->setOrderVector($vector);
	}

	return $this->orderVector;
	}


	/**
	* @task order
	*/
	protected function getDefaultOrderVector() {
	return array('id');
	}


	/**
	* @task order
	*/
	public function getOrderableColumns() {
	$cache = PhabricatorCaches::getRequestCache();
	$class = get_class($this);
	$cache_key = 'query.orderablecolumns.'.$class;

	$columns = $cache->getKey($cache_key);
	if ($columns !== null) {
	return $columns;
	}

	$columns = array(
	'id' => array(
	'table' => $this->getPrimaryTableAlias(),
	'column' => 'id',
	'reverse' => false,
	'type' => 'int',
	'unique' => true,
	),
	);

	$object = $this->newResultObject();
	if ($object instanceof PhabricatorCustomFieldInterface) {
	$list = PhabricatorCustomField::getObjectFields(
	$object,
	PhabricatorCustomField::ROLE_APPLICATIONSEARCH);
	foreach ($list->getFields() as $field) {
	$index = $field->buildOrderIndex();
	if (!$index) {
	continue;
	}

	$digest = $field->getFieldIndex();

	$key = $field->getModernFieldKey();

	$columns[$key] = array(
	'table' => 'appsearch_order_'.$digest,
	'column' => 'indexValue',
	'type' => $index->getIndexValueType(),
	'null' => 'tail',
	'customfield' => true,
	'customfield.index.table' => $index->getTableName(),
	'customfield.index.key' => $digest,
	);
	}
	}

	$cache->setKey($cache_key, $columns);

	return $columns;
	}


	/**
	* @task order
	*/
	final protected function buildOrderClause(AphrontDatabaseConnection $conn) {
	$orderable = $this->getOrderableColumns();
	$vector = $this->getOrderVector();

	$parts = array();
	foreach ($vector as $order) {
	$part = $orderable[$order->getOrderKey()];
	if ($order->getIsReversed()) {
	$part['reverse'] = !idx($part, 'reverse', false);
	}
	$parts[] = $part;
	}

	return $this->formatOrderClause($conn, $parts);
	}


	/**
	* @task order
	*/
	protected function formatOrderClause(
	AphrontDatabaseConnection $conn,
	array $parts) {

	$is_query_reversed = false;
	if ($this->getBeforeID()) {
	$is_query_reversed = !$is_query_reversed;
	}

	$sql = array();
	foreach ($parts as $key => $part) {
	$is_column_reversed = !empty($part['reverse']);

	$descending = true;
	if ($is_query_reversed) {
	$descending = !$descending;
	}

	if ($is_column_reversed) {
	$descending = !$descending;
	}

	$table = idx($part, 'table');
	$column = $part['column'];

	if ($table !== null) {
	$field = qsprintf($conn, '%T.%T', $table, $column);
	} else {
	$field = qsprintf($conn, '%T', $column);
	}

	$null = idx($part, 'null');
	if ($null) {
	switch ($null) {
	case 'head':
	$null_field = qsprintf($conn, '(%Q IS NULL)', $field);
	break;
	case 'tail':
	$null_field = qsprintf($conn, '(%Q IS NOT NULL)', $field);
	break;
	default:
	throw new Exception(
	pht(
	'NULL value "%s" is invalid. Valid values are "head" and '.
	'"tail".',
	$null));
	}

	if ($descending) {
	$sql[] = qsprintf($conn, '%Q DESC', $null_field);
	} else {
	$sql[] = qsprintf($conn, '%Q ASC', $null_field);
	}
	}

	if ($descending) {
	$sql[] = qsprintf($conn, '%Q DESC', $field);
	} else {
	$sql[] = qsprintf($conn, '%Q ASC', $field);
	}
	}

	return qsprintf($conn, 'ORDER BY %Q', implode(', ', $sql));
	}


	/* -( Application Search )------------------------------------------------- */


	/**
	* Constrain the query with an ApplicationSearch index, requiring field values
	* contain at least one of the values in a set.
	*
	* This constraint can build the most common types of queries, like:
	*
	* - Find users with shirt sizes "X" or "XL".
	* - Find shoes with size "13".
	*
	* @param PhabricatorCustomFieldIndexStorage Table where the index is stored.
	* @param string\|list<string> One or more values to filter by.
	* @return this
	* @task appsearch
	*/
	public function withApplicationSearchContainsConstraint(
	PhabricatorCustomFieldIndexStorage $index,
	$value) {

	$this->applicationSearchConstraints[] = array(
	'type' => $index->getIndexValueType(),
	'cond' => '=',
	'table' => $index->getTableName(),
	'index' => $index->getIndexKey(),
	'value' => $value,
	);

	return $this;
	}


	/**
	* Constrain the query with an ApplicationSearch index, requiring values
	* exist in a given range.
	*
	* This constraint is useful for expressing date ranges:
	*
	* - Find events between July 1st and July 7th.
	*
	* The ends of the range are inclusive, so a `$min` of `3` and a `$max` of
	* `5` will match fields with values `3`, `4`, or `5`. Providing `null` for
	* either end of the range will leave that end of the constraint open.
	*
	* @param PhabricatorCustomFieldIndexStorage Table where the index is stored.
	* @param int\|null Minimum permissible value, inclusive.
	* @param int\|null Maximum permissible value, inclusive.
	* @return this
	* @task appsearch
	*/
	public function withApplicationSearchRangeConstraint(
	PhabricatorCustomFieldIndexStorage $index,
	$min,
	$max) {

	$index_type = $index->getIndexValueType();
	if ($index_type != 'int') {
	throw new Exception(
	pht(
	'Attempting to apply a range constraint to a field with index type '.
	'"%s", expected type "%s".',
	$index_type,
	'int'));
	}

	$this->applicationSearchConstraints[] = array(
	'type' => $index->getIndexValueType(),
	'cond' => 'range',
	'table' => $index->getTableName(),
	'index' => $index->getIndexKey(),
	'value' => array($min, $max),
	);

	return $this;
	}


	/**
	* Get the name of the query's primary object PHID column, for constructing
	* JOIN clauses. Normally (and by default) this is just `"phid"`, but it may
	* be something more exotic.
	*
	* See @{method:getPrimaryTableAlias} if the column needs to be qualified with
	* a table alias.
	*
	* @return string Column name.
	* @task appsearch
	*/
	protected function getApplicationSearchObjectPHIDColumn() {
	if ($this->getPrimaryTableAlias()) {
	$prefix = $this->getPrimaryTableAlias().'.';
	} else {
	$prefix = '';
	}

	return $prefix.'phid';
	}


	/**
	* Determine if the JOINs built by ApplicationSearch might cause each primary
	* object to return multiple result rows. Generally, this means the query
	* needs an extra GROUP BY clause.
	*
	* @return bool True if the query may return multiple rows for each object.
	* @task appsearch
	*/
	protected function getApplicationSearchMayJoinMultipleRows() {
	foreach ($this->applicationSearchConstraints as $constraint) {
	$type = $constraint['type'];
	$value = $constraint['value'];
	$cond = $constraint['cond'];

	switch ($cond) {
	case '=':
	switch ($type) {
	case 'string':
	case 'int':
	if (count((array)$value) > 1) {
	return true;
	}
	break;
	default:
	throw new Exception(pht('Unknown index type "%s"!', $type));
	}
	break;
	case 'range':
	// NOTE: It's possible to write a custom field where multiple rows
	// match a range constraint, but we don't currently ship any in the
	// upstream and I can't immediately come up with cases where this
	// would make sense.
	break;
	default:
	throw new Exception(pht('Unknown constraint condition "%s"!', $cond));
	}
	}

	return false;
	}


	/**
	* Construct a GROUP BY clause appropriate for ApplicationSearch constraints.
	*
	* @param AphrontDatabaseConnection Connection executing the query.
	* @return string Group clause.
	* @task appsearch
	*/
	protected function buildApplicationSearchGroupClause(
	AphrontDatabaseConnection $conn_r) {

	if ($this->getApplicationSearchMayJoinMultipleRows()) {
	return qsprintf(
	$conn_r,
	'GROUP BY %Q',
	$this->getApplicationSearchObjectPHIDColumn());
	} else {
	return '';
	}
	}


	/**
	* Construct a JOIN clause appropriate for applying ApplicationSearch
	* constraints.
	*
	* @param AphrontDatabaseConnection Connection executing the query.
	* @return string Join clause.
	* @task appsearch
	*/
	protected function buildApplicationSearchJoinClause(
	AphrontDatabaseConnection $conn_r) {

	$joins = array();
	foreach ($this->applicationSearchConstraints as $key => $constraint) {
	$table = $constraint['table'];
	$alias = 'appsearch_'.$key;
	$index = $constraint['index'];
	$cond = $constraint['cond'];
	$phid_column = $this->getApplicationSearchObjectPHIDColumn();
	switch ($cond) {
	case '=':
	$type = $constraint['type'];
	switch ($type) {
	case 'string':
	$constraint_clause = qsprintf(
	$conn_r,
	'%T.indexValue IN (%Ls)',
	$alias,
	(array)$constraint['value']);
	break;
	case 'int':
	$constraint_clause = qsprintf(
	$conn_r,
	'%T.indexValue IN (%Ld)',
	$alias,
	(array)$constraint['value']);
	break;
	default:
	throw new Exception(pht('Unknown index type "%s"!', $type));
	}

	$joins[] = qsprintf(
	$conn_r,
	'JOIN %T %T ON %T.objectPHID = %Q
	AND %T.indexKey = %s
	AND (%Q)',
	$table,
	$alias,
	$alias,
	$phid_column,
	$alias,
	$index,
	$constraint_clause);
	break;
	case 'range':
	list($min, $max) = $constraint['value'];
	if (($min === null) && ($max === null)) {
	// If there's no actual range constraint, just move on.
	break;
	}

	if ($min === null) {
	$constraint_clause = qsprintf(
	$conn_r,
	'%T.indexValue <= %d',
	$alias,
	$max);
	} else if ($max === null) {
	$constraint_clause = qsprintf(
	$conn_r,
	'%T.indexValue >= %d',
	$alias,
	$min);
	} else {
	$constraint_clause = qsprintf(
	$conn_r,
	'%T.indexValue BETWEEN %d AND %d',
	$alias,
	$min,
	$max);
	}

	$joins[] = qsprintf(
	$conn_r,
	'JOIN %T %T ON %T.objectPHID = %Q
	AND %T.indexKey = %s
	AND (%Q)',
	$table,
	$alias,
	$alias,
	$phid_column,
	$alias,
	$index,
	$constraint_clause);
	break;
	default:
	throw new Exception(pht('Unknown constraint condition "%s"!', $cond));
	}
	}

	$phid_column = $this->getApplicationSearchObjectPHIDColumn();
	$orderable = $this->getOrderableColumns();

	$vector = $this->getOrderVector();
	foreach ($vector as $order) {
	$spec = $orderable[$order->getOrderKey()];
	if (empty($spec['customfield'])) {
	continue;
	}

	$table = $spec['customfield.index.table'];
	$alias = $spec['table'];
	$key = $spec['customfield.index.key'];

	$joins[] = qsprintf(
	$conn_r,
	'LEFT JOIN %T %T ON %T.objectPHID = %Q
	AND %T.indexKey = %s',
	$table,
	$alias,
	$alias,
	$phid_column,
	$alias,
	$key);
	}

	return implode(' ', $joins);
	}


	/* -( Integration with CustomField )--------------------------------------- */


	/**
	* @task customfield
	*/
	protected function getPagingValueMapForCustomFields(
	PhabricatorCustomFieldInterface $object) {

	// We have to get the current field values on the cursor object.
	$fields = PhabricatorCustomField::getObjectFields(
	$object,
	PhabricatorCustomField::ROLE_APPLICATIONSEARCH);
	$fields->setViewer($this->getViewer());
	$fields->readFieldsFromStorage($object);

	$map = array();
	foreach ($fields->getFields() as $field) {
	$map['custom:'.$field->getFieldKey()] = $field->getValueForStorage();
	}

	return $map;
	}


	/**
	* @task customfield
	*/
	protected function isCustomFieldOrderKey($key) {
	$prefix = 'custom:';
	return !strncmp($key, $prefix, strlen($prefix));
	}


	/* -( Ngrams )------------------------------------------------------------- */


	protected function withNgramsConstraint(
	PhabricatorSearchNgrams $index,
	$value) {

	if (strlen($value)) {
	$this->ngrams[] = array(
	'index' => $index,
	'value' => $value,
	'length' => count(phutil_utf8v($value)),
	);
	}

	return $this;
	}


	protected function buildNgramsJoinClause(AphrontDatabaseConnection $conn) {
	$flat = array();
	foreach ($this->ngrams as $spec) {
	$index = $spec['index'];
	$value = $spec['value'];
	$length = $spec['length'];

	if ($length >= 3) {
	$ngrams = $index->getNgramsFromString($value, 'query');
	$prefix = false;
	} else if ($length == 2) {
	$ngrams = $index->getNgramsFromString($value, 'prefix');
	$prefix = false;
	} else {
	$ngrams = array(' '.$value);
	$prefix = true;
	}

	foreach ($ngrams as $ngram) {
	$flat[] = array(
	'table' => $index->getTableName(),
	'ngram' => $ngram,
	'prefix' => $prefix,
	);
	}
	}

	// MySQL only allows us to join a maximum of 61 tables per query. Each
	// ngram is going to cost us a join toward that limit, so if the user
	// specified a very long query string, just pick 16 of the ngrams
	// at random.
	if (count($flat) > 16) {
	shuffle($flat);
	$flat = array_slice($flat, 0, 16);
	}

	$alias = $this->getPrimaryTableAlias();
	if ($alias) {
	$id_column = qsprintf($conn, '%T.%T', $alias, 'id');
	} else {
	$id_column = qsprintf($conn, '%T', 'id');
	}

	$idx = 1;
	$joins = array();
	foreach ($flat as $spec) {
	$table = $spec['table'];
	$ngram = $spec['ngram'];
	$prefix = $spec['prefix'];

	$alias = 'ngm'.$idx++;

	if ($prefix) {
	$joins[] = qsprintf(
	$conn,
	'JOIN %T %T ON %T.objectID = %Q AND %T.ngram LIKE %>',
	$table,
	$alias,
	$alias,
	$id_column,
	$alias,
	$ngram);
	} else {
	$joins[] = qsprintf(
	$conn,
	'JOIN %T %T ON %T.objectID = %Q AND %T.ngram = %s',
	$table,
	$alias,
	$alias,
	$id_column,
	$alias,
	$ngram);
	}
	}

	return $joins;
	}


	protected function buildNgramsWhereClause(AphrontDatabaseConnection $conn) {
	$where = array();

	foreach ($this->ngrams as $ngram) {
	$index = $ngram['index'];
	$value = $ngram['value'];

	$column = $index->getColumnName();
	$alias = $this->getPrimaryTableAlias();
	if ($alias) {
	$column = qsprintf($conn, '%T.%T', $alias, $column);
	} else {
	$column = qsprintf($conn, '%T', $column);
	}

	$tokens = $index->tokenizeString($value);
	foreach ($tokens as $token) {
	$where[] = qsprintf(
	$conn,
	'%Q LIKE %~',
	$column,
	$token);
	}
	}

	return $where;
	}


	protected function shouldGroupNgramResultRows() {
	return (bool)$this->ngrams;
	}


	/* -( Edge Logic )--------------------------------------------------------- */


	/**
	* Convenience method for specifying edge logic constraints with a list of
	* PHIDs.
	*
	* @param const Edge constant.
	* @param const Constraint operator.
	* @param list<phid> List of PHIDs.
	* @return this
	* @task edgelogic
	*/
	public function withEdgeLogicPHIDs($edge_type, $operator, array $phids) {
	$constraints = array();
	foreach ($phids as $phid) {
	$constraints[] = new PhabricatorQueryConstraint($operator, $phid);
	}

	return $this->withEdgeLogicConstraints($edge_type, $constraints);
	}


	/**
	* @task edgelogic
	*/
	public function withEdgeLogicConstraints($edge_type, array $constraints) {
	assert_instances_of($constraints, 'PhabricatorQueryConstraint');

	$constraints = mgroup($constraints, 'getOperator');
	foreach ($constraints as $operator => $list) {
	foreach ($list as $item) {
	$this->edgeLogicConstraints[$edge_type][$operator][] = $item;
	}
	}

	$this->edgeLogicConstraintsAreValid = false;

	return $this;
	}


	/**
	* @task edgelogic
	*/
	public function buildEdgeLogicSelectClause(AphrontDatabaseConnection $conn) {
	$select = array();

	$this->validateEdgeLogicConstraints();

	foreach ($this->edgeLogicConstraints as $type => $constraints) {
	foreach ($constraints as $operator => $list) {
	$alias = $this->getEdgeLogicTableAlias($operator, $type);
	switch ($operator) {
	case PhabricatorQueryConstraint::OPERATOR_AND:
	if (count($list) > 1) {
	$select[] = qsprintf(
	$conn,
	'COUNT(DISTINCT(%T.dst)) %T',
	$alias,
	$this->buildEdgeLogicTableAliasCount($alias));
	}
	break;
	case PhabricatorQueryConstraint::OPERATOR_ANCESTOR:
	// This is tricky. We have a query which specifies multiple
	// projects, each of which may have an arbitrarily large number
	// of descendants.

	// Suppose the projects are "Engineering" and "Operations", and
	// "Engineering" has subprojects X, Y and Z.

	// We first use `FIELD(dst, X, Y, Z)` to produce a 0 if a row
	// is not part of Engineering at all, or some number other than
	// 0 if it is.

	// Then we use `IF(..., idx, NULL)` to convert the 0 to a NULL and
	// any other value to an index (say, 1) for the ancestor.

	// We build these up for every ancestor, then use `COALESCE(...)`
	// to select the non-null one, giving us an ancestor which this
	// row is a member of.

	// From there, we use `COUNT(DISTINCT(...))` to make sure that
	// each result row is a member of all ancestors.
	if (count($list) > 1) {
	$idx = 1;
	$parts = array();
	foreach ($list as $constraint) {
	$parts[] = qsprintf(
	$conn,
	'IF(FIELD(%T.dst, %Ls) != 0, %d, NULL)',
	$alias,
	(array)$constraint->getValue(),
	$idx++);
	}
	$parts = implode(', ', $parts);

	$select[] = qsprintf(
	$conn,
	'COUNT(DISTINCT(COALESCE(%Q))) %T',
	$parts,
	$this->buildEdgeLogicTableAliasAncestor($alias));
	}
	break;
	default:
	break;
	}
	}
	}

	return $select;
	}


	/**
	* @task edgelogic
	*/
	public function buildEdgeLogicJoinClause(AphrontDatabaseConnection $conn) {
	$edge_table = PhabricatorEdgeConfig::TABLE_NAME_EDGE;
	$phid_column = $this->getApplicationSearchObjectPHIDColumn();

	$joins = array();
	foreach ($this->edgeLogicConstraints as $type => $constraints) {

	$op_null = PhabricatorQueryConstraint::OPERATOR_NULL;
	$has_null = isset($constraints[$op_null]);

	foreach ($constraints as $operator => $list) {
	$alias = $this->getEdgeLogicTableAlias($operator, $type);

	$phids = array();
	foreach ($list as $constraint) {
	$value = (array)$constraint->getValue();
	foreach ($value as $v) {
	$phids[$v] = $v;
	}
	}
	$phids = array_keys($phids);

	switch ($operator) {
	case PhabricatorQueryConstraint::OPERATOR_NOT:
	$joins[] = qsprintf(
	$conn,
	'LEFT JOIN %T %T ON %Q = %T.src AND %T.type = %d
	AND %T.dst IN (%Ls)',
	$edge_table,
	$alias,
	$phid_column,
	$alias,
	$alias,
	$type,
	$alias,
	$phids);
	break;
	case PhabricatorQueryConstraint::OPERATOR_ANCESTOR:
	case PhabricatorQueryConstraint::OPERATOR_AND:
	case PhabricatorQueryConstraint::OPERATOR_OR:
	// If we're including results with no matches, we have to degrade
	// this to a LEFT join. We'll use WHERE to select matching rows
	// later.
	if ($has_null) {
	$join_type = 'LEFT';
	} else {
	$join_type = '';
	}

	$joins[] = qsprintf(
	$conn,
	'%Q JOIN %T %T ON %Q = %T.src AND %T.type = %d
	AND %T.dst IN (%Ls)',
	$join_type,
	$edge_table,
	$alias,
	$phid_column,
	$alias,
	$alias,
	$type,
	$alias,
	$phids);
	break;
	case PhabricatorQueryConstraint::OPERATOR_NULL:
	$joins[] = qsprintf(
	$conn,
	'LEFT JOIN %T %T ON %Q = %T.src AND %T.type = %d',
	$edge_table,
	$alias,
	$phid_column,
	$alias,
	$alias,
	$type);
	break;
	}
	}
	}

	return $joins;
	}


	/**
	* @task edgelogic
	*/
	public function buildEdgeLogicWhereClause(AphrontDatabaseConnection $conn) {
	$where = array();

	foreach ($this->edgeLogicConstraints as $type => $constraints) {

	$full = array();
	$null = array();

	$op_null = PhabricatorQueryConstraint::OPERATOR_NULL;
	$has_null = isset($constraints[$op_null]);

	foreach ($constraints as $operator => $list) {
	$alias = $this->getEdgeLogicTableAlias($operator, $type);
	switch ($operator) {
	case PhabricatorQueryConstraint::OPERATOR_NOT:
	$full[] = qsprintf(
	$conn,
	'%T.dst IS NULL',
	$alias);
	break;
	case PhabricatorQueryConstraint::OPERATOR_AND:
	case PhabricatorQueryConstraint::OPERATOR_OR:
	if ($has_null) {
	$full[] = qsprintf(
	$conn,
	'%T.dst IS NOT NULL',
	$alias);
	}
	break;
	case PhabricatorQueryConstraint::OPERATOR_NULL:
	$null[] = qsprintf(
	$conn,
	'%T.dst IS NULL',
	$alias);
	break;
	}
	}

	if ($full && $null) {
	$full = $this->formatWhereSubclause($full);
	$null = $this->formatWhereSubclause($null);
	$where[] = qsprintf($conn, '(%Q OR %Q)', $full, $null);
	} else if ($full) {
	foreach ($full as $condition) {
	$where[] = $condition;
	}
	} else if ($null) {
	foreach ($null as $condition) {
	$where[] = $condition;
	}
	}
	}

	return $where;
	}


	/**
	* @task edgelogic
	*/
	public function buildEdgeLogicHavingClause(AphrontDatabaseConnection $conn) {
	$having = array();

	foreach ($this->edgeLogicConstraints as $type => $constraints) {
	foreach ($constraints as $operator => $list) {
	$alias = $this->getEdgeLogicTableAlias($operator, $type);
	switch ($operator) {
	case PhabricatorQueryConstraint::OPERATOR_AND:
	if (count($list) > 1) {
	$having[] = qsprintf(
	$conn,
	'%T = %d',
	$this->buildEdgeLogicTableAliasCount($alias),
	count($list));
	}
	break;
	case PhabricatorQueryConstraint::OPERATOR_ANCESTOR:
	if (count($list) > 1) {
	$having[] = qsprintf(
	$conn,
	'%T = %d',
	$this->buildEdgeLogicTableAliasAncestor($alias),
	count($list));
	}
	break;
	}
	}
	}

	return $having;
	}


	/**
	* @task edgelogic
	*/
	public function shouldGroupEdgeLogicResultRows() {
	foreach ($this->edgeLogicConstraints as $type => $constraints) {
	foreach ($constraints as $operator => $list) {
	switch ($operator) {
	case PhabricatorQueryConstraint::OPERATOR_NOT:
	case PhabricatorQueryConstraint::OPERATOR_AND:
	case PhabricatorQueryConstraint::OPERATOR_OR:
	case PhabricatorQueryConstraint::OPERATOR_ANCESTOR:
	if (count($list) > 1) {
	return true;
	}
	break;
	case PhabricatorQueryConstraint::OPERATOR_NULL:
	return true;
	}
	}
	}

	return false;
	}


	/**
	* @task edgelogic
	*/
	private function getEdgeLogicTableAlias($operator, $type) {
	return 'edgelogic_'.$operator.'_'.$type;
	}


	/**
	* @task edgelogic
	*/
	private function buildEdgeLogicTableAliasCount($alias) {
	return $alias.'_count';
	}

	/**
	* @task edgelogic
	*/
	private function buildEdgeLogicTableAliasAncestor($alias) {
	return $alias.'_ancestor';
	}


	/**
	* Select certain edge logic constraint values.
	*
	* @task edgelogic
	*/
	protected function getEdgeLogicValues(
	array $edge_types,
	array $operators) {

	$values = array();

	$constraint_lists = $this->edgeLogicConstraints;
	if ($edge_types) {
	$constraint_lists = array_select_keys($constraint_lists, $edge_types);
	}

	foreach ($constraint_lists as $type => $constraints) {
	if ($operators) {
	$constraints = array_select_keys($constraints, $operators);
	}
	foreach ($constraints as $operator => $list) {
	foreach ($list as $constraint) {
	$value = (array)$constraint->getValue();
	foreach ($value as $v) {
	$values[] = $v;
	}
	}
	}
	}

	return $values;
	}


	/**
	* Validate edge logic constraints for the query.
	*
	* @return this
	* @task edgelogic
	*/
	private function validateEdgeLogicConstraints() {
	if ($this->edgeLogicConstraintsAreValid) {
	return $this;
	}

	foreach ($this->edgeLogicConstraints as $type => $constraints) {
	foreach ($constraints as $operator => $list) {
	switch ($operator) {
	case PhabricatorQueryConstraint::OPERATOR_EMPTY:
	throw new PhabricatorEmptyQueryException(
	pht('This query specifies an empty constraint.'));
	}
	}
	}

	// This should probably be more modular, eventually, but we only do
	// project-based edge logic today.

	$project_phids = $this->getEdgeLogicValues(
	array(
	PhabricatorProjectObjectHasProjectEdgeType::EDGECONST,
	),
	array(
	PhabricatorQueryConstraint::OPERATOR_AND,
	PhabricatorQueryConstraint::OPERATOR_OR,
	PhabricatorQueryConstraint::OPERATOR_NOT,
	PhabricatorQueryConstraint::OPERATOR_ANCESTOR,
	));
	if ($project_phids) {
	$projects = id(new PhabricatorProjectQuery())
	->setViewer($this->getViewer())
	->setParentQuery($this)
	->withPHIDs($project_phids)
	->execute();
	$projects = mpull($projects, null, 'getPHID');
	foreach ($project_phids as $phid) {
	if (empty($projects[$phid])) {
	throw new PhabricatorEmptyQueryException(
	pht(
	'This query is constrained by a project you do not have '.
	'permission to see.'));
	}
	}
	}

	$this->edgeLogicConstraintsAreValid = true;

	return $this;
	}


	/* -( Spaces )------------------------------------------------------------- */


	/**
	* Constrain the query to return results from only specific Spaces.
	*
	* Pass a list of Space PHIDs, or `null` to represent the default space. Only
	* results in those Spaces will be returned.
	*
	* Queries are always constrained to include only results from spaces the
	* viewer has access to.
	*
	* @param list<phid\|null>
	* @task spaces
	*/
	public function withSpacePHIDs(array $space_phids) {
	$object = $this->newResultObject();

	if (!$object) {
	throw new Exception(
	pht(
	'This query (of class "%s") does not implement newResultObject(), '.
	'but must implement this method to enable support for Spaces.',
	get_class($this)));
	}

	if (!($object instanceof PhabricatorSpacesInterface)) {
	throw new Exception(
	pht(
	'This query (of class "%s") returned an object of class "%s" from '.
	'getNewResultObject(), but it does not implement the required '.
	'interface ("%s"). Objects must implement this interface to enable '.
	'Spaces support.',
	get_class($this),
	get_class($object),
	'PhabricatorSpacesInterface'));
	}

	$this->spacePHIDs = $space_phids;

	return $this;
	}

	public function withSpaceIsArchived($archived) {
	$this->spaceIsArchived = $archived;
	return $this;
	}


	/**
	* Constrain the query to include only results in valid Spaces.
	*
	* This method builds part of a WHERE clause which considers the spaces the
	* viewer has access to see with any explicit constraint on spaces added by
	* @{method:withSpacePHIDs}.
	*
	* @param AphrontDatabaseConnection Database connection.
	* @return string Part of a WHERE clause.
	* @task spaces
	*/
	private function buildSpacesWhereClause(AphrontDatabaseConnection $conn) {
	$object = $this->newResultObject();
	if (!$object) {
	return null;
	}

	if (!($object instanceof PhabricatorSpacesInterface)) {
	return null;
	}

	$viewer = $this->getViewer();

	// If we have an omnipotent viewer and no formal space constraints, don't
	// emit a clause. This primarily enables older migrations to run cleanly,
	// without fataling because they try to match a `spacePHID` column which
	// does not exist yet. See T8743, T8746.
	if ($viewer->isOmnipotent()) {
	if ($this->spaceIsArchived === null && $this->spacePHIDs === null) {
	return null;
	}
	}

	$space_phids = array();
	$include_null = false;

	$all = PhabricatorSpacesNamespaceQuery::getAllSpaces();
	if (!$all) {
	// If there are no spaces at all, implicitly give the viewer access to
	// the default space.
	$include_null = true;
	} else {
	// Otherwise, give them access to the spaces they have permission to
	// see.
	$viewer_spaces = PhabricatorSpacesNamespaceQuery::getViewerSpaces(
	$viewer);
	foreach ($viewer_spaces as $viewer_space) {
	if ($this->spaceIsArchived !== null) {
	if ($viewer_space->getIsArchived() != $this->spaceIsArchived) {
	continue;
	}
	}
	$phid = $viewer_space->getPHID();
	$space_phids[$phid] = $phid;
	if ($viewer_space->getIsDefaultNamespace()) {
	$include_null = true;
	}
	}
	}

	// If we have additional explicit constraints, evaluate them now.
	if ($this->spacePHIDs !== null) {
	$explicit = array();
	$explicit_null = false;
	foreach ($this->spacePHIDs as $phid) {
	if ($phid === null) {
	$space = PhabricatorSpacesNamespaceQuery::getDefaultSpace();
	} else {
	$space = idx($all, $phid);
	}

	if ($space) {
	$phid = $space->getPHID();
	$explicit[$phid] = $phid;
	if ($space->getIsDefaultNamespace()) {
	$explicit_null = true;
	}
	}
	}

	// If the viewer can see the default space but it isn't on the explicit
	// list of spaces to query, don't match it.
	if ($include_null && !$explicit_null) {
	$include_null = false;
	}

	// Include only the spaces common to the viewer and the constraints.
	$space_phids = array_intersect_key($space_phids, $explicit);
	}

	if (!$space_phids && !$include_null) {
	if ($this->spacePHIDs === null) {
	throw new PhabricatorEmptyQueryException(
	pht('You do not have access to any spaces.'));
	} else {
	throw new PhabricatorEmptyQueryException(
	pht(
	'You do not have access to any of the spaces this query '.
	'is constrained to.'));
	}
	}

	$alias = $this->getPrimaryTableAlias();
	if ($alias) {
	$col = qsprintf($conn, '%T.spacePHID', $alias);
	} else {
	$col = 'spacePHID';
	}

	if ($space_phids && $include_null) {
	return qsprintf(
	$conn,
	'(%Q IN (%Ls) OR %Q IS NULL)',
	$col,
	$space_phids,
	$col);
	} else if ($space_phids) {
	return qsprintf(
	$conn,
	'%Q IN (%Ls)',
	$col,
	$space_phids);
	} else {
	return qsprintf(
	$conn,
	'%Q IS NULL',
	$col);
	}
	}

	}

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