@jahed/sparql-engine/src/operators/join/hash-join-table.ts

SPARQL query engine for servers and web browsers.

// SPDX-License-Identifier: MIT
import type { Bindings } from "../../rdf/bindings.ts";

/**
 * A HashJoinTable is used by a Hash-based join to save set of bindings corresponding to a joinKey.
 * All bindings corresponding to the save value of the joinKey are aggregated in a list.
 */
export default class HashJoinTable {
  private readonly _content: Map<string, Bindings[]>;
  constructor() {
    this._content = new Map();
  }

  /**
   * Register a pair (value, bindings).
   * @param key - Key used to save the bindings
   * @param bindings - Bindings to save
   */
  put(key: string, bindings: Bindings): void {
    if (!this._content.has(key)) {
      this._content.set(key, []);
    }
    const old: Bindings[] = this._content.get(key)!;
    this._content.set(key, old.concat([bindings]));
  }

  /**
   * Perform a join between a set of bindings and all set of bindings in the table associated with the key.
   * Returns an empty list if there is no join results.
   * @param  key  - Key used to fetch set of set of bindings
   * @param  bindings - Bindings to join with
   * @return Join results, or an empty list if there is none.
   */
  join(key: string, bindings: Bindings): Bindings[] {
    if (!this._content.has(key)) {
      return [];
    }
    return this._content.get(key)!.map((b: Bindings) => b.union(bindings));
  }
}