@jahed/sparql-engine/dist/engine/stages/service-stage-builder.js

SPARQL query engine for servers and web browsers.

import { Wildcard } from "sparqljs";
import ExecutionContext from "../context/execution-context.js";
import ContextSymbols from "../context/symbols.js";
import { Pipeline } from "../pipeline/pipeline.js";
import StageBuilder from "./stage-builder.js";
/**
 * A ServiceStageBuilder is responsible for evaluation a SERVICE clause in a SPARQL query.
 */
export default class ServiceStageBuilder extends StageBuilder {
    /**
     * Build a {@link PipelineStage} to evaluate a SERVICE clause
     * @param  source  - Input {@link PipelineStage}
     * @param  node    - Service clause
     * @param  options - Execution options
     * @return A {@link PipelineStage} used to evaluate a SERVICE clause
     */
    async execute(source, node, context) {
        let subquery;
        if (node.patterns[0].type === "query") {
            subquery = node.patterns[0];
        }
        else {
            subquery = {
                prefixes: context.getProperty(ContextSymbols.PREFIXES),
                queryType: "SELECT",
                variables: [new Wildcard()],
                type: "query",
                where: node.patterns,
            };
        }
        const iri = node.name;
        if (!this.dataset.getDefaultGraph().iri.equals(iri) &&
            !this.dataset.hasNamedGraph(iri)) {
            const graph = await this.dataset.createGraph(iri);
            this.dataset.addNamedGraph(graph);
        }
        let handler = undefined;
        if (node.silent) {
            handler = () => {
                return Pipeline.getInstance().empty();
            };
        }
        return Pipeline.getInstance().catch(await this._buildIterator(source, iri, subquery, context), handler);
    }
    /**
     * Returns a {@link PipelineStage} used to evaluate a SERVICE clause
     * @abstract
     * @param source    - Input {@link PipelineStage}
     * @param iri       - Iri of the SERVICE clause
     * @param subquery  - Subquery to be evaluated
     * @param options   - Execution options
     * @return A {@link PipelineStage} used to evaluate a SERVICE clause
     */
    async _buildIterator(source, iri, subquery, context) {
        const opts = context.clone();
        opts.defaultGraphs = [iri];
        return this._builder._buildQueryPlan(subquery, opts, source);
    }
}
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