mungedb-aggregate/lib/pipeline/DepsTracker.js

"use strict";

/**
 * Allows components in an aggregation pipeline to report what they need from their input.
 *
 * @class DepsTracker
 * @namespace mungedb-aggregate.pipeline
 * @module mungedb-aggregate
 * @constructor
 */
var DepsTracker = module.exports = function DepsTracker() {
    /* fields is a set of strings */
    this.fields = {};
    this.needWholeDocument = false;
    this.needTextScore = false;
}, klass = DepsTracker, base = Object, proto = klass.prototype = Object.create(base.prototype, {constructor:{value:klass}});

var ParsedDeps = require("./ParsedDeps");

/**
 * Returns a projection object covering the dependencies tracked by this class.
 *
 * @method toProjection
 * @return {Object} projection of caller's dependencies
 */
proto.toProjection = function toProjection() {
    var proj = {};

    // if(this.needTextScore) {
        // bb.append(Document::metaFieldTextScore, BSON("$meta" << "textScore"));
    // }

    if (this.needWholeDocument) {
        return proj;
    }

    if (Object.keys(this.fields).length === 0) {
        // Projection language lacks good a way to say no fields needed. This fakes it.
        proj._id = 0;
        proj.$noFieldsNeeded = 1;
        return proj;
    }

    var last = "",
        needId = false;

    Object.keys(this.fields).sort().forEach(function (it) {
        if (it.slice(0,3) == "_id" && (it.length == 3 || it.charAt(3) == ".")) {
            // _id and subfields are handled specially due in part to SERVER-7502
            needId = true;
            return;
        }

        if (last !== "" && it.slice(0, last.length) === last) {
            // we are including a parent of *it so we don't need to include this
            // field explicitly. In fact, due to SERVER-6527 if we included this
            // field, the parent wouldn't be fully included. This logic relies
            // on on set iterators going in lexicographic order so that a string
            // is always directly before of all fields it prefixes.
            return;
        }

        last = it + ".";
        proj[it] = 1;
    });

    if (needId)
        proj._id = 1;
    else
        proj._id = 0;

    return proj;
};

/**
 * Takes a depsTracker and builds a simple recursive lookup table out of it.
 *
 * @method toParsedDeps
 * @return {ParsedDeps}
 */
proto.toParsedDeps = function toParsedDeps() {
    var doc = {};

    if(this.needWholeDocument || this.needTextScore) {
        // can't use ParsedDeps in this case
        // TODO: not sure what appropriate equivalent to boost::none is
        return;
    }

    var last = "";
    Object.keys(this.fields).sort().forEach(function (it) {
        if (last !== "" && it.slice(0, last.length) === last) {
            // we are including a parent of *it so we don't need to include this
            // field explicitly. In fact, due to SERVER-6527 if we included this
            // field, the parent wouldn't be fully included. This logic relies
            // on on set iterators going in lexicographic order so that a string
            // is always directly before of all fields it prefixes.
            return;
        }

        last = it + ".";
        // TODO: set nested field to true; i.e. a.b.c = true, not a = true
        doc[it] = true;
    });

    return new ParsedDeps(doc);
};