Mongoose, Select a specific field with find

问题:

I'm trying to select only a specific field with

exports.someValue = function(req, res, next) {
    //query with mongoose
    var query = dbSchemas.SomeValue.find({}).select('name');

    query.exec(function (err, someValue) {
        if (err) return next(err);
        res.send(someValue);
    });
};

But in my json response i'm receiving also the _id, my document schema only has two fiels, _id and name

[{"_id":70672,"name":"SOME VALUE 1"},{"_id":71327,"name":"SOME VALUE 2"}]

Why???

回答1:

The _id field is always present unless you explicitly exclude it. Do so using the - syntax:

exports.someValue = function(req, res, next) {
    //query with mongoose
    var query = dbSchemas.SomeValue.find({}).select('name -_id');

    query.exec(function (err, someValue) {
        if (err) return next(err);
        res.send(someValue);
    });
};

Or explicitly via an object:

exports.someValue = function(req, res, next) {
    //query with mongoose
    var query = dbSchemas.SomeValue.find({}).select({ "name": 1, "_id": 0});

    query.exec(function (err, someValue) {
        if (err) return next(err);
        res.send(someValue);
    });
};

回答2:

There is a shorter way of doing this now:

exports.someValue = function(req, res, next) {
    //query with mongoose
    dbSchemas.SomeValue.find({}, 'name', function(err, someValue){
      if(err) return next(err);
      res.send(someValue);
    });
    //this eliminates the .select() and .exec() methods
};

In case you want most of the Schema fields and want to omit only a few, you can prefix the field name with a -. For ex "-name" in the second argument will not include name field in the doc whereas the example given here will have only the name field in the returned docs.

回答3:

There's a better way to handle it using Native MongoDB code in Mongoose.

exports.getUsers = function(req, res, next) {

    var usersProjection = { 
        __v: false,
        _id: false
    };

    User.find({}, usersProjection, function (err, users) {
        if (err) return next(err);
        res.json(users);
    });    
}

http://docs.mongodb.org/manual/reference/method/db.collection.find/

Note:

var usersProjection

The list of objects listed here will not be returned / printed.

回答4:

DB Data

[
  {
    "_id": "70001",
    "name": "peter"
  },
  {
    "_id": "70002",
    "name": "john"
  },
  {
    "_id": "70003",
    "name": "joseph"
  }
]

Query

db.collection.find({},
{
  "_id": 0,
  "name": 1
}).exec((Result)=>{
    console.log(Result);
})

Output:

[
  {
    "name": "peter"
  },
  {
    "name": "john"
  },
  {
    "name": "joseph"
  }
]

Working sample playground

link

回答5:

The precise way to do this is it to use .project() cursor method with the new mongodb and nodejs driver.

var query = await dbSchemas.SomeValue.find({}).project({ name: 1, _id: 0 })