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query.service.ts
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Sun, May 26, 18:34

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({});
/**
* Gets the data from an endpoint via http post
*
* @param baseUrl: The url of the endpoint.
* @param query: The query to run.
* @param queryType: "CONSTRUCT" or "QUERY"
* @returns the response.
*/
public getData(baseUrl: string, 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(baseUrl, query, httpOptions);
} else {
httpOptions = { headers: new HttpHeaders({ 'Content-Type': 'application/sparql-query',
'Accept': 'application/sparql-results+json; charset=UTF-8'})};
return this.http.post(baseUrl, query, httpOptions);
}
}
/**
* 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);
} );
}
/**
* getQueryForItem()
* Parametrizes a given baseQuery with a iri passed, so the iri will be the subject of the where clause
*
* @param itemIri: The iri of the selected resource
* @param baseQuery: name of the query to parametrize
* @returns the query for the resource.
*/
public parametrizeQueryWithItem(baseQuery: string, itemIri: string) {
const parsedQuery = this.parser.parse(baseQuery);
// console.log('parsedQuery', parsedQuery);
// parametrize/reset the subject iri to the word's iri we like to query for
const resourceOfInterest = {'termType': 'NamedNode', 'value': decodeURI(itemIri) };
parsedQuery.where[0].triples[0].subject = resourceOfInterest;
// generate the new query string and return it
// console.log('parametrized query', this.sparqlGenerator.stringify(parsedQuery));
return this.sparqlGenerator.stringify(parsedQuery);
}
}

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