mungedb-aggregate/lib/pipeline/expressions/ObjectExpression.js

"use strict";

/**
 * Create an empty expression.  Until fields are added, this will evaluateInternal to an empty document (object).
 * @class ObjectExpression
 * @namespace mungedb-aggregate.pipeline.expressions
 * @module mungedb-aggregate
 * @extends mungedb-aggregate.pipeline.expressions.Expression
 * @constructor
 **/
var ObjectExpression = module.exports = function ObjectExpression(atRoot) {
		this.fixedArity(1);
		if (arguments.length !== 1) throw new Error("one arg expected");
		this.excludeId = false; /// <Boolean> for if _id is to be excluded
		this.atRoot = atRoot;
		this._expressions = {}; /// <Object<Expression>> mapping from fieldname to Expression to generate the value NULL expression means include from source document
		this._order = []; /// <Array<String>> this is used to maintain order for generated fields not in the source document
}, klass = ObjectExpression,
		Expression = require("./Expression"),
		base = Expression,
		proto = klass.prototype = Object.create(base.prototype, {
				constructor: {
						value: klass
				}
		});

// DEPENDENCIES
var Document = require("../Document"),
		FieldPath = require("../FieldPath");

// INSTANCE VARIABLES
/**
 * <Boolean> for if _id is to be excluded
 * @property excludeId
 **/
proto.excludeId = undefined;

/**
 * <Object<Expression>> mapping from fieldname to Expression to generate the value NULL expression means include from source document
 **/
proto._expressions = undefined;

//TODO: might be able to completely ditch _order everywhere in here since `Object`s are mostly ordered anyhow but need to come back and revisit that later
/**
 * <Array<String>> this is used to maintain order for generated fields not in the source document
 **/
proto._order = [];


// PROTOTYPE MEMBERS

/**
 * evaluateInternal(), but return a Document instead of a Value-wrapped Document.
 * @method evaluateDocument
 * @param currentDoc the input Document
 * @returns the result document
 **/
proto.evaluateDocument = function evaluateDocument(vars) {
		// create and populate the result
		var pResult = {};
		this.addToDocument(pResult, pResult, vars); // No inclusion field matching.
		return pResult;
};

proto.evaluateInternal = function evaluateInternal(vars) { //TODO: collapse with #evaluateDocument()?
		return this.evaluateDocument(vars);
};

proto.optimize = function optimize() {
		for (var key in this._expressions) {
				var expr = this._expressions[key];
				if (expr !== undefined && expr !== null) this._expressions[key] = expr.optimize();
		}
		return this;
};

proto.getIsSimple = function getIsSimple() {
		for (var key in this._expressions) {
				var expr = this._expressions[key];
				if (expr !== undefined && expr !== null && !expr.getIsSimple()) return false;
		}
		return true;
};

proto.addDependencies = function addDependencies(deps, path) {
		var pathStr = "";
		if (path instanceof Array) {
				if (path.length === 0) {
						// we are in the top level of a projection so _id is implicit
						if (!this.excludeId) deps.fields[Document.ID_PROPERTY_NAME] = 1;
				} else {
						pathStr = new FieldPath(path).getPath() + ".";
				}
		} else {
				if (this.excludeId) throw new Error("excludeId is true!");
		}
		for (var key in this._expressions) {
				var expr = this._expressions[key];
				if (expr !== undefined && expr !== null) {
						if (path instanceof Array) path.push(key);
						expr.addDependencies(deps.fields, path);
						if (path instanceof Array) path.pop();
				} else { // inclusion
						if (path === undefined || path === null) throw new Error("inclusion not supported in objects nested in $expressions; uassert code 16407");
						deps.fields[pathStr + key] = 1;
				}
		}
		//Array.prototype.push.apply(deps, Object.getOwnPropertyNames(depsSet));
		for (key in deps.fields) {
				deps[key] = 1;
		}
		return deps; // NOTE: added to munge as a convenience
};

/**
 * evaluateInternal(), but add the evaluated fields to a given document instead of creating a new one.
 * @method addToDocument
 * @param pResult the Document to add the evaluated expressions to
 * @param currentDoc the input Document for this level
 * @param vars the root of the whole input document
 **/
proto.addToDocument = function addToDocument(pResult, currentDoc, vars) {


		var doneFields = {}; // This is used to mark fields we've done so that we can add the ones we haven't

		for (var fieldName in currentDoc) {
				if (!currentDoc.hasOwnProperty(fieldName)) continue;
				var fieldValue = currentDoc[fieldName];

				// This field is not supposed to be in the output (unless it is _id)
				if (!this._expressions.hasOwnProperty(fieldName)) {
						if (!this.excludeId && this.atRoot && fieldName == Document.ID_PROPERTY_NAME) {
								// _id from the root doc is always included (until exclusion is supported)
								// not updating doneFields since "_id" isn't in _expressions
								pResult[fieldName] = fieldValue;
						}
						continue;
				}

				// make sure we don't add this field again
				doneFields[fieldName] = true;

				// This means pull the matching field from the input document
				var expr = this._expressions[fieldName];
				if (!(expr instanceof Expression)) {
						pResult[fieldName] = fieldValue;
						continue;
				}

				// Check if this expression replaces the whole field
				if (!(fieldValue instanceof Object) || (fieldValue.constructor !== Object && fieldValue.constructor !== Array) || !(expr instanceof ObjectExpression)) {
						var pValue = expr.evaluateInternal(vars);

						// don't add field if nothing was found in the subobject
						if (expr instanceof ObjectExpression && pValue instanceof Object && Object.getOwnPropertyNames(pValue).length === 0) continue;

						// Don't add non-existent values (note:  different from NULL); this is consistent with existing selection syntax which doesn't force the appearnance of non-existent fields.
						// TODO make missing distinct from Undefined
						if (pValue !== undefined) pResult[fieldName] = pValue;
						continue;
				}

				// Check on the type of the input value.  If it's an object, just walk down into that recursively, and add it to the result.
				if (fieldValue instanceof Object && fieldValue.constructor === Object) {
						pResult[fieldName] = expr.addToDocument({}, fieldValue, vars); //TODO: pretty sure this is broken;
				} else if (fieldValue instanceof Object && fieldValue.constructor === Array) {
						// If it's an array, we have to do the same thing, but to each array element.  Then, add the array of results to the current document.
						var result = [];
						for (var fvi = 0, fvl = fieldValue.length; fvi < fvl; fvi++) {
								var subValue = fieldValue[fvi];
								if (subValue.constructor !== Object) continue; // can't look for a subfield in a non-object value.
								result.push(expr.addToDocument({}, subValue, vars));
						}
						pResult[fieldName] = result;
				} else {
						throw new Error("should never happen"); //verify( false );
				}
		}

		if (Object.getOwnPropertyNames(doneFields).length == Object.getOwnPropertyNames(this._expressions).length) return pResult; //NOTE: munge returns result as a convenience

		// add any remaining fields we haven't already taken care of
		for (var i = 0, l = this._order.length; i < l; i++) {
				var fieldName2 = this._order[i];
				var expr2 = this._expressions[fieldName2];

				// if we've already dealt with this field, above, do nothing
				if (doneFields.hasOwnProperty(fieldName2)) continue;

				// this is a missing inclusion field
				if (!expr2) continue;

				var value = expr2.evaluateInternal(vars);

				// Don't add non-existent values (note:  different from NULL); this is consistent with existing selection syntax which doesn't force the appearnance of non-existent fields.
				if (value === undefined) continue;

				// don't add field if nothing was found in the subobject
				if (expr2 instanceof ObjectExpression && value && value instanceof Object && Object.getOwnPropertyNames(value) == {}) continue;

				pResult[fieldName2] = value;
		}

		return pResult; //NOTE: munge returns result as a convenience
};

/**
 * estimated number of fields that will be output
 * @method getSizeHint
 **/
proto.getSizeHint = function getSizeHint() {
		// Note: this can overestimate, but that is better than underestimating
		return Object.getOwnPropertyNames(this._expressions).length + (this.excludeId ? 0 : 1);
};

/**
 * Add a field to the document expression.
 * @method addField
 * @param fieldPath the path the evaluated expression will have in the result Document
 * @param pExpression the expression to evaluateInternal obtain this field's Value in the result Document
 **/
proto.addField = function addField(fieldPath, pExpression) {
		if (!(fieldPath instanceof FieldPath)) fieldPath = new FieldPath(fieldPath);
		var fieldPart = fieldPath.fields[0],
				haveExpr = this._expressions.hasOwnProperty(fieldPart),
				subObj = this._expressions[fieldPart]; // inserts if !haveExpr //NOTE: not in munge & JS it doesn't, handled manually below

		if (!haveExpr) {
				this._order.push(fieldPart);
		} else { // we already have an expression or inclusion for this field
				if (fieldPath.getPathLength() == 1) { // This expression is for right here
						if (!(subObj instanceof ObjectExpression && typeof pExpression == "object" && pExpression instanceof ObjectExpression)) {
								throw new Error("can't add an expression for field `" + fieldPart + "` because there is already an expression for that field or one of its sub-fields; uassert code 16400"); // we can merge them
						}

						// Copy everything from the newSubObj to the existing subObj
						// This is for cases like { $project:{ 'b.c':1, b:{ a:1 } } }
						for (var key in pExpression._expressions) {
								if (pExpression._expressions.hasOwnProperty(key)) {
										subObj.addField(key, pExpression._expressions[key]); // asserts if any fields are dupes
								}
						}
						return;
				} else { // This expression is for a subfield
						if (!subObj) throw new Error("can't add an expression for a subfield of `" + fieldPart + "` because there is already an expression that applies to the whole field; uassert code 16401");
				}
		}

		if (fieldPath.getPathLength() == 1) {
				if (haveExpr) throw new Error("Internal error."); // haveExpr case handled above.
				this._expressions[fieldPart] = pExpression;
				return;
		}

		if (!haveExpr) subObj = this._expressions[fieldPart] = new ObjectExpression();

		subObj.addField(fieldPath.tail(), pExpression);
};

/**
 * Add a field path to the set of those to be included.
 *
 * Note that including a nested field implies including everything on the path leading down to it.
 *
 * @method includePath
 * @param fieldPath the name of the field to be included
 **/
proto.includePath = function includePath(path) {
		this.addField(path, undefined);
};

/**
 * Get a count of the added fields.
 * @method getFieldCount
 * @returns how many fields have been added
 **/
proto.getFieldCount = function getFieldCount() {
		return Object.getOwnPropertyNames(this._expressions).length;
};

///**
//* Specialized BSON conversion that allows for writing out a $project specification.
//* This creates a standalone object, which must be added to a containing object with a name
//*
//* @param pBuilder where to write the object to
//* @param requireExpression see Expression::addToBsonObj
//**/
//TODO:	proto.documentToBson = ...?
//TODO:	proto.addToBsonObj = ...?
//TODO: proto.addToBsonArray = ...?

//NOTE: in `munge` we're not passing the `Object`s in and allowing `toJSON` (was `documentToBson`) to modify it directly and are instead building and returning a new `Object` since that's the way it's actually used
proto.toJSON = function toJSON(requireExpression) {
		var o = {};
		if (this.excludeId) o[Document.ID_PROPERTY_NAME] = false;
		for (var i = 0, l = this._order.length; i < l; i++) {
				var fieldName = this._order[i];
				if (!this._expressions.hasOwnProperty(fieldName)) throw new Error("internal error: fieldName from _ordered list not found in _expressions");
				var fieldValue = this._expressions[fieldName];
				if (fieldValue === undefined) {
						o[fieldName] = true; // this is inclusion, not an expression
				} else {
						o[fieldName] = fieldValue.toJSON(requireExpression);
				}
		}
		return o;
};