mongodb query builder

mongo_utils.js

//query builder
var q = new (function() {
    this.has = function(key, exists) {
        if (typeof exists === 'undefined') {
            //default, query for documents that has they key.
            exists = true;
        }

        var query = {};
        query[key] = {$exists: exists};
        return query;
    };

    this.typeNames = {
        Double: 1,
        String: 2,
        Object: 3,
        Array: 4,
        Binary: 5,
        Id: 7,
        Boolean: 8,
        Date: 9,
        Null: 10,
        RegExp: 11,
        Javascript: 13,
        Symbol: 14,
        JavascriptWithScope: 15,
        Int32: 16,
        Timestamp: 17,
        Int64: 18
    };

    this.size = function(key, n) {
        var query = {};
        query[key] = {$size: n};
        return query;
    };

    this.is = function(key, typeName) {
        if (typeName === 'Array') {
            //special case for mangodb. https://jira.mongodb.org/browse/SERVER-1475
            return this.or(this.has(key + '.0'), this.size(key, 0));
        } 

        var type = this.typeNames[typeName];
        return this.and(this.has(key + '.0', false), this.eq(key, {$type: type}));
    };
    
    this.and = function() {
        var args = Array.slice(arguments);
        return {$and: args};
    };

    this.or = function() {
        var args = Array.slice(arguments);
        return {$or: args};
    };


    this.nempty = function(key) {
        return this.ne(key, '', this.has(key));
    };

    this.eq = function(key, val) {
        var query = {};
        query[key] = val;
        return query;
    };
    
    this.ne = function(key, val, query) {
        if (!query) {
            query = {};
        }
        if (!query[key]) {
            query[key] = {};
        } 
        query[key]['$ne'] = val;
        return query;
    };

    this.match = function(key, re) {
        var query = {};
        query[key] = {$regex: re};
        return query;
    };

    this.show = function() {
        var args = Array.slice(arguments);
        var projection = {};
        args.forEach(function(arg) {
            projection[arg] = 1;
        });
        return projection;
    };
});

// convenience
var u = new (function() {
    var me = this;

    var DEFAULT_COLLECTION = db.Listing;
    var DEFAULT_PROJECTION = 'metadata.url';

    me.projection = function(key) {
        return q.show(DEFAULT_PROJECTION, key);
    };

    me.distinct = function(key) {
        var collection = COLLECTION || DEFAULT_COLLECTION;
        return collection.distinct(key);
    };

    me.find_has = function(key) {
        var collection =  COLLECTION || DEFAULT_COLLECTION;
        return collection.find(q.has(key), me.projection(key));
    };
    
    me.find_nempty = function(key) {
        var collection = COLLECTION ||  DEFAULT_COLLECTION;
        return collection.find(q.nempty(key), me.projection(key));
    };

    me.find_ne = function(key, val) {
        var collection = COLLECTION ||  DEFAULT_COLLECTION;
        return collection.find(q.and(q.has(key), q.ne(key, val)), me.projection(key));
    };
    me.find_eq = function(key, val) {
        var collection = COLLECTION ||  DEFAULT_COLLECTION;
        return collection.find(q.eq(key, val), me.projection(key));
    };

    me.find_match = function(key, regex) {
        var collection = COLLECTION ||  DEFAULT_COLLECTION;
        return collection.find(q.match(key, regex), me.projection(key));
    };
});