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PhabricatorPolicyQuery.php
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Fri, Nov 8, 05:50

PhabricatorPolicyQuery.php
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<?php
/*
* Copyright 2012 Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/**
* A @{class:PhabricatorQuery} which filters results according to visibility
* policies for the querying user. Broadly, this class allows you to implement
* a query that returns only objects the user is allowed to see.
*
* $results = id(new ExampleQuery())
* ->setViewer($user)
* ->withConstraint($example)
* ->execute();
*
* Normally, you should extend @{class:PhabricatorCursorPagedPolicyQuery}, not
* this class. @{class:PhabricatorCursorPagedPolicyQuery} provides a more
* practical interface for building usable queries against most object types.
*
* NOTE: Although this class extends @{class:PhabricatorOffsetPagedQuery},
* offset paging with policy filtering is not efficient. All results must be
* loaded into the application and filtered here: skipping `N` rows via offset
* is an `O(N)` operation with a large constant. Prefer cursor-based paging
* with @{class:PhabricatorCursorPagedPolicyQuery}, which can filter far more
* efficiently in MySQL.
*
* @task config Query Configuration
* @task exec Executing Queries
* @task policyimpl Policy Query Implementation
*/
abstract class PhabricatorPolicyQuery extends PhabricatorOffsetPagedQuery {
private $viewer;
private $raisePolicyExceptions;
private $rawResultLimit;
/* -( Query Configuration )------------------------------------------------ */
/**
* Set the viewer who is executing the query. Results will be filtered
* according to the viewer's capabilities. You must set a viewer to execute
* a policy query.
*
* @param PhabricatorUser The viewing user.
* @return this
* @task config
*/
final public function setViewer(PhabricatorUser $viewer) {
$this->viewer = $viewer;
return $this;
}
/**
* Get the query's viewer.
*
* @return PhabricatorUser The viewing user.
* @task config
*/
final public function getViewer() {
return $this->viewer;
}
/* -( Query Execution )---------------------------------------------------- */
/**
* Execute the query, expecting a single result. This method simplifies
* loading objects for detail pages or edit views.
*
* // Load one result by ID.
* $obj = id(new ExampleQuery())
* ->setViewer($user)
* ->withIDs(array($id))
* ->executeOne();
* if (!$obj) {
* return new Aphront404Response();
* }
*
* If zero results match the query, this method returns `null`.
*
* If one result matches the query, this method returns that result.
*
* If two or more results match the query, this method throws an exception.
* You should use this method only when the query constraints guarantee at
* most one match (e.g., selecting a specific ID or PHID).
*
* If one result matches the query but it is caught by the policy filter (for
* example, the user is trying to view or edit an object which exists but
* which they do not have permission to see) a policy exception is thrown.
*
* @return mixed Single result, or null.
* @task exec
*/
final public function executeOne() {
$this->raisePolicyExceptions = true;
try {
$results = $this->execute();
} catch (Exception $ex) {
$this->raisePolicyExceptions = false;
throw $ex;
}
if (count($results) > 1) {
throw new Exception("Expected a single result!");
}
if (!$results) {
return null;
}
return head($results);
}
/**
* Execute the query, loading all visible results.
*
* @return list<PhabricatorPolicyInterface> Result objects.
* @task exec
*/
final public function execute() {
if (!$this->viewer) {
throw new Exception("Call setViewer() before execute()!");
}
$results = array();
$filter = new PhabricatorPolicyFilter();
$filter->setViewer($this->viewer);
$filter->setCapability(PhabricatorPolicyCapability::CAN_VIEW);
$filter->raisePolicyExceptions($this->raisePolicyExceptions);
$offset = (int)$this->getOffset();
$limit = (int)$this->getLimit();
$count = 0;
$need = null;
if ($offset) {
$need = $offset + $limit;
}
$this->willExecute();
do {
// Figure out how many results to load. "0" means "all results".
$load = 0;
if ($need && ($count < $offset)) {
// This cap is just an arbitrary limit to keep memory usage from going
// crazy for large offsets; we can't execute them efficiently, but
// it should be possible to execute them without crashing.
$load = min($need, 1024);
} else if ($limit) {
// Otherwise, just load the number of rows we're after. Note that it
// might be more efficient to load more rows than this (if we expect
// about 5% of objects to be filtered, loading 105% of the limit might
// be better) or fewer rows than this (if we already have 95 rows and
// only need 100, loading only 5 rows might be better), but we currently
// just use the simplest heuristic since we don't have enough data
// about policy queries in the real world to tweak it.
$load = $limit;
}
$this->rawResultLimit = $load;
$page = $this->loadPage();
$visible = $filter->apply($page);
foreach ($visible as $key => $result) {
++$count;
// If we have an offset, we just ignore that many results and start
// storing them only once we've hit the offset. This reduces memory
// requirements for large offsets, compared to storing them all and
// slicing them away later.
if ($count > $offset) {
$results[$key] = $result;
}
if ($need && ($count >= $need)) {
// If we have all the rows we need, break out of the paging query.
break 2;
}
}
if (!$load) {
// If we don't have a load count, we loaded all the results. We do
// not need to load another page.
break;
}
if (count($page) < $load) {
// If we have a load count but the unfiltered results contained fewer
// objects, we know this was the last page of objects; we do not need
// to load another page because we can deduce it would be empty.
break;
}
$this->nextPage($page);
} while (true);
return $results;
}
/* -( Policy Query Implementation )---------------------------------------- */
/**
* Get the number of results @{method:loadPage} should load. If the value is
* 0, @{method:loadPage} should load all available results.
*
* @return int The number of results to load, or 0 for all results.
* @task policyimpl
*/
final protected function getRawResultLimit() {
return $this->rawResultLimit;
}
/**
* Hook invoked before query execution. Generally, implementations should
* reset any internal cursors.
*
* @return void
* @task policyimpl
*/
protected function willExecute() {
return;
}
/**
* Load a raw page of results. Generally, implementations should load objects
* from the database. They should attempt to return the number of results
* hinted by @{method:getRawResultLimit}.
*
* @return list<PhabricatorPolicyInterface> List of filterable policy objects.
* @task policyimpl
*/
abstract protected function loadPage();
/**
* Update internal state so that the next call to @{method:loadPage} will
* return new results. Generally, you should adjust a cursor position based
* on the provided result page.
*
* @param list<PhabricatorPolicyInterface> The current page of results.
* @return void
* @task policyimpl
*/
abstract protected function nextPage(array $page);
}

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