How to use mongoose findOne

问题:

I have the below schema (apologies that it is in coffeescript)

Schema = mongoose.Schema

AuthS = new Schema
    auth:   {type: String, unique: true}
    nick:   String
    time:   Date
Auth = mongoose.model 'Auth', AuthS

I simply want to recover one record which is definitely in my database:

Auth.findOne({nick: 'noname'}, function(obj) { console.log(obj); });

Unfortunately this always logs null. db.auths.findOne({nick: 'noname'}) in mongo shell always returns a value. What is going on?

回答1:

Found the problem, need to use function(err,obj) instead:

Auth.findOne({nick: 'noname'}, function(err,obj) { console.log(obj); });

回答2:

Mongoose basically wraps mongodb's api to give you a pseudo relational db api so queries are not going to be exactly like mongodb queries. Mongoose findOne query returns a query object, not a document. You can either use a callback as the solution suggests or as of v4+ findOne returns a thenable so you can use .then or await/async to retrieve the document.

// thenables
Auth.findOne({nick: 'noname'}).then(err, result) {console.log(result)};
Auth.findOne({nick: 'noname'}).then(function (doc) {console.log(doc)});

// To use a full fledge promise you will need to use .exec()
var auth = Auth.findOne({nick: 'noname'}).exec();
auth.then(function (doc) {console.log(doc)});

// async/await
async function auth() {
  const doc = await Auth.findOne({nick: 'noname'}).exec();
  return doc;
}
auth();

See the docs if you would like to use a third party promise library.

回答3:

You might want to consider using console.log with the built-in "arguments" object:

console.log(arguments); // would have shown you [0] null, [1] yourResult

This will always output all of your arguments, no matter how many arguments you have.

回答4:

Use obj[0].nick and you will get desired result,

回答5:

In my case same error is there , I am using Asyanc / Await functions , for this needs to add AWAIT for findOne

Ex:const foundUser = User.findOne ({ "email" : req.body.email });

above , foundUser always contains Object value in both cases either user found or not because it's returning values before finishing findOne .

const foundUser = await User.findOne ({ "email" : req.body.email });

above , foundUser returns null if user is not there in collection with provided condition . If user found returns user document.