gistfile1.js

var MongooseFilter = function (schema, options) {
    options = options || {};
    
    schema.pre('save', function (next) {
        this.filter();
        next();
    });
    
    schema.method('filter', function () {
        var self = this;
        var paths = schema.paths;
        if (!'_id' in paths) paths['_id'] = '';
        for (var key in this._doc) {
            if (!(key in paths)) {
                delete this._doc[key];
                if (options.debug) console.log('Warn: Cannot put ' + key + ' in ' + this.constructor.modelName);
            }
        }
        return this; 
    });

};