在MongoDB中可以直接引用ObjectID，但在Mongoose中则不能

Question

The first code snippet achieves the desired effect:

//in mongodb console:
db.collection.update({"username":"name"}, {$pull : { "task" : { "_id" : ObjectId("55280205702c316b6d79c89c")}}})

Yet this second (seemingly equivalent) code snippet written in Mongoose does not:

//in Mongoose:
var taskID = "55280205702c316b6d79c88c"
var pull = { $pull : {}};
var idObj = {};
idObj["_id"] = taskID;
pull.$pull["task"] = idObj;

collectionModel.update({"username": "name"}, pull) //fails to work since taskID just shows up as a literal string 55280205702c316b6d79c88c instead of ObjectId("55280205702c316b6d79c88c")

Other things I've tried:

• making var taskID equal to the string 'ObjectId(\\"55280205702c316b6d79c88c\\")'
• setting var taskID equal to mongoose.Types.ObjectId("55280205702c316b6d79c88c")

How can I achieve the effect in the former code snippet in Mongoose?

Answer 1

Import ObjectId type and use it in your query :

var ObjectId = require('mongoose').Types.ObjectId; 
idObj["_id"] = new ObjectId("55280205702c316b6d79c88c");

Answer 2

After you did the $pull operation in mongodb shell and tried the same update operation in Mongoose with the same ObjectId, it didn't work because the task array object element with "_id": ObjectId("55280205702c316b6d79c88c") was removed by the previous mongodb shell operation.

Try first running the same query from Mongoose but with a different and existing taskID which is cast to ObjectId. You could add an extension to the String object as follows:

String.prototype.toObjectId = function() {
    var ObjectId = (require("mongoose").Types.ObjectId);
    return new ObjectId(this.toString());
};

var taskID = "55280205702c316b6d79c88d".toObjectId(); // a different _id
collectionModel.update( 
    { "username": "name" }, 
    { "$pull" : { "task": { "_id": taskID } } }, 
    function (err, result) {
        console.log(result);        
    }
);