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

"use strict";
var AndExpression = module.exports = (function(){
	// CONSTRUCTOR
	/** 
	 * Create an expression that finds the conjunction of n operands. The
	 * conjunction uses short-circuit logic; the expressions are evaluated in the
	 * order they were added to the conjunction, and the evaluation stops and
	 * returns false on the first operand that evaluates to false.
	 *
	 * @class AndExpression
	 * @namespace mungedb.aggregate.pipeline.expressions
	 * @module mungedb-aggregate
	 * @constructor
	 **/
	var klass = module.exports = function AndExpression(){
		if(arguments.length !== 0) throw new Error("zero args expected");
		base.call(this);
	}, base = require("./NaryExpression"), proto = klass.prototype = Object.create(base.prototype, {constructor:{value:klass}});

	// DEPENDENCIES
	var Value = require("../Value"),
		ConstantExpression = require("./ConstantExpression"),
		CoerceToBoolExpression = require("./CoerceToBoolExpression");

	// PROTOTYPE MEMBERS
	proto.getOpName = function getOpName(){
		return "$and";
	};

	proto.getFactory = function getFactory(){
		return klass;	// using the ctor rather than a separate .create() method
	};

	/**
	 * Takes an array one or more values and returns true if all of the values in the array are true. Otherwise $and returns false.
	 * @method evaluate
	 **/
	proto.evaluate = function evaluate(doc) {
		for (var i = 0, n = this.operands.length; i < n; ++i) {
			var value = this.operands[i].evaluate(doc);
			if (!Value.coerceToBool(value)) return false;
		}
		return true;
	};

	proto.optimize = function optimize() {
		var expr = base.prototype.optimize.call(this); //optimize the conjunction as much as possible

		// if the result isn't a conjunction, we can't do anything
		if (!(expr instanceof AndExpression)) return expr;
		var andExpr = expr;

		// Check the last argument on the result; if it's not constant (as promised by ExpressionNary::optimize(),) then there's nothing we can do.
		var n = andExpr.operands.length;
		// ExpressionNary::optimize() generates an ExpressionConstant for {$and:[]}.
		if (!n) throw new Error("requires operands!");
		var lastExpr = andExpr.operands[n - 1];
		if (!(lastExpr instanceof ConstantExpression)) return expr;

		// Evaluate and coerce the last argument to a boolean.  If it's false, then we can replace this entire expression.
		var last = Value.coerceToBool(lastExpr.evaluate());
		if (!last) return new ConstantExpression(false);

		// If we got here, the final operand was true, so we don't need it anymore.
		// If there was only one other operand, we don't need the conjunction either.
		// Note we still need to keep the promise that the result will be a boolean.
		if (n == 2) return new CoerceToBoolExpression(andExpr.operands[0]);

		//Remove the final "true" value, and return the new expression.
		//CW TODO: Note that because of any implicit conversions, we may need to apply an implicit boolean conversion.
		andExpr.operands.length = n - 1; //truncate the array
		return expr;
	};

//TODO:	proto.toMatcherBson

	return klass;
})();