@jahed/sparql-engine/dist/operators/modifiers/construct.js

SPARQL query engine for servers and web browsers.

// SPDX-License-Identifier: MIT
import { compact } from "lodash-es";
import { Pipeline } from "../../engine/pipeline/pipeline.js";
import { isVariable, tripleToQuad } from "../../utils/rdf.js";
/**
 * A ConstructOperator transform solution mappings into RDF triples, according to a template
 * @see {@link https://www.w3.org/TR/2013/REC-sparql11-query-20130321/#construct}
 * @param source  - Source {@link PipelineStage}
 * @param templates - Set of triples patterns in the CONSTRUCT clause
 * @return A {@link PipelineStage} which evaluate the CONSTRUCT modifier
 */
export default function construct(source, query) {
    const rawTriples = [];
    const templates = (query.template || [])
        .map((t) => tripleToQuad(t))
        .filter((t) => {
        if (isVariable(t.subject) ||
            isVariable(t.predicate) ||
            isVariable(t.object)) {
            return true;
        }
        rawTriples.push(t);
        return false;
    });
    const engine = Pipeline.getInstance();
    return engine.endWith(engine.flatMap(source, (bindings) => {
        return compact(templates.map((t) => bindings.bound(t)));
    }), rawTriples);
}
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