将MongoDB结果string化为NodeJs的http响应

我想要发送一个查询到我的MongoDB在MongoHQ一个现有的ID。 这个查询的结果需要发送给用户的响应。 如果我logging这个查询的结果，我得到了JSON响应。 现在，如果我将相同的结果串起来，我得到以下错误：

TypeError：将圆形结构转换为JSON

代码：

http.createServer(function(request, response) { var tweety = db.find({"tweetId":"1337"}); console.log(tweety); response.end(JSON.stringify(tweety)); }).listen(3000); 

我从console.log（）获得的JSON：

 { _mongooseOptions: {}, mongooseCollection: { collection: { db: [Object], collectionName: 'posts', internalHint: null, opts: {}, slaveOk: false, serializeFunctions: false, raw: false, pkFactory: [Object], serverCapabilities: undefined }, opts: { bufferCommands: true, capped: false }, name: 'posts', conn: { base: [Object], collections: [Object], models: [Object], replica: false, hosts: null, host: 'dogen.mongohq.com', port: 10004, user: 'x', pass: 'x', name: 'TwitterBitcoin', options: [Object], otherDbs: [], _readyState: 1, _closeCalled: false, _hasOpened: true, _listening: true, _events: {}, db: [Object] }, queue: [], buffer: false }, model: { [Function: model] base: { connections: [Object], plugins: [], models: [Object], modelSchemas: [Object], options: [Object] }, modelName: 'Post', model: [Function: model], db: { base: [Object], collections: [Object], models: [Object], replica: false, hosts: null, host: 'dogen.mongohq.com', port: 10004, user: 'x', pass: 'x', name: 'TwitterBitcoin', options: [Object], otherDbs: [], _readyState: 1, _closeCalled: false, _hasOpened: true, _listening: true, _events: {}, db: [Object] }, discriminators: undefined, schema: { paths: [Object], subpaths: {}, virtuals: [Object], nested: {}, inherits: {}, callQueue: [], _indexes: [], methods: {}, statics: {}, tree: [Object], _requiredpaths: [], discriminatorMapping: undefined, _indexedpaths: undefined, options: [Object], _events: {} }, options: undefined, collection: { collection: [Object], opts: [Object], name: 'posts', conn: [Object], queue: [], buffer: false } }, op: 'find', options: {}, _conditions: { tweetId: '527920990878433280' }, _fields: undefined, _update: undefined, _path: undefined, _distinct: undefined, _collection: { collection: { collection: [Object], opts: [Object], name: 'posts', conn: [Object], queue: [], buffer: false } }, _castError: null } 

我如何发送JSON结果作为回应？