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query.service.ts
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Thu, May 23, 05:22

query.service.ts
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import { Injectable } from '@angular/core';
import { Parser, Generator, Wildcard } from 'sparqljs';
import {HttpClient, HttpHeaders} from '@angular/common/http';
@Injectable()
export class QueryService {
constructor(private http: HttpClient) {
}
parser = new Parser();
sparqlGenerator = new Generator({});
// prefixes and namespaces for shrinking iri's to the enduser
// TODO: move namespaces to a file and read it in
namespaces = {
data: 'http://rdfh.ch/projects/0068#',
owl: 'http://www.w3.org/2002/07/owl#',
rdfs: 'http://www.w3.org/1999/02/22-rdf-syntax-ns#',
tln: 'http://www.nie.org/ontology/nietzsche#',
};
baseUrl = 'http://fuseki.nie-ine.ch/nietzsche-rw/query';
/**
* Gets the data from an endpoint via http post
*
* @param query: The query to run.
* @param queryType: "CONSTRUCT" or "QUERY"
* @returns the response.
*/
public getData(query: string, queryType?: string ) {
let httpOptions;
if (queryType === 'CONSTRUCT') {
// A construct does contain a text as response, not a json, so responseType must be 'text' to avoid parse errors
httpOptions = { headers: new HttpHeaders({'Content-Type': 'application/sparql-query', 'Accept': 'text/turtle'}),
responseType: 'text'};
return this.http.post(this.baseUrl, query, httpOptions);
} else { httpOptions = { headers: new HttpHeaders({ 'Content-Type': 'application/sparql-query',
'Accept': 'application/sparql-results+json; charset=UTF-8'})};
}
if (this.baseUrl && httpOptions.headers && (query === undefined || query === null || query === '') ) {
console.log('fallback to static query as there is no query passed');
this.getQueryfromFilename('fallbackQuery.rq' ).subscribe(fallbackQuery => {
console.log('fallbackQuery: ', fallbackQuery);
return this.http.post(this.baseUrl, query, httpOptions);
});
} else { return this.http.post(this.baseUrl, query, httpOptions); }
}
/**
* Shrinks an iri according to the defined prefixes/namespaces.
*
* @param iri The iri to be shrunken.
* @returns shrunkIri: the shrunken iri if it can be shrunken.
*/
public shrink_iri(iri) {
let shrunkIri: string;
Object.keys(this.namespaces).forEach((ns, index) => {
// console.log(this.namespaces[ns] + ' key ' + ns )
if (iri.includes(this.namespaces[ns])) {
shrunkIri = iri.replace(this.namespaces[ns], ns + ':' );
}
});
if (shrunkIri) { return shrunkIri; } else {return iri; }
}
/**
* Gets all the properties and connected resources of one thing. Gets it depending on its type or role:
* if the thing is a property, it gets all connected ?s and ?o;
* if it's usage as subject is of interest, it gets all ?p and ?o;
* if it's usage as object is of interest, it gets all ?s ?p;
*
* @param iri: The iri of the selected resource
* @param resourceType: the type of usage i.e. as ?s, ?p or ?o
* @returns the query for the resource.
*/
public getQueryforResourceData(iri: string, resourceType?: string) {
const parsedQuery = this.parser.parse('SELECT ?s ?p ?o WHERE { ?s ?p ?o }');
// reset the subject iri to the word's iri we like to query for
const resource = {'termType': 'NamedNode', 'value': decodeURI(iri) };
switch (resourceType) {
case 'subject': {
parsedQuery.where[0].triples[0].subject = resource;
break; }
case 'predicate': {
parsedQuery.where[0].triples[0].predicate = resource;
break; }
case 'object': {
parsedQuery.where[0].triples[0].object = resource;
break; }
}
// generate the new query string and return it
return this.sparqlGenerator.stringify(parsedQuery);
}
/**
* Gets a text file by its name from the directory assets/queries.
*
* @param filename The name of the file + file name extension.
* @returns the text of the file.
*/
public getQueryfromFilename(filename) {
return this.http.get('../assets/queries/' + filename, {responseType: 'text'});
}
/**
* Gets a query string from a given file in the directory assets/queries.
*
* @param filename The name of the file + file name extension.
* @returns The JSON equivalence of the parsed query.
*/
public parseQueryFromFile(filename) {
return this.getQueryfromFilename(filename )
.subscribe(query => {
this.parser.parse(query);
} );
}
private setWhereIri(query, index, iri) {
if (query.queryType === 'CONSTRUCT') {
query.where[index].patterns[0].triples[0].subject.id = iri;
} else { query = '';
}
return query;
}
}

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