Comparing mongoose _id and strings

user_1442258 0
Viewed 158973

I have a node.js application that pulls some data and sticks it into an object, like this:

var results = new Object();

User.findOne(query, function(err, u) {
    results.userId = u._id;
}

When I do an if/then based on that stored ID, the comparison is never true:

if (results.userId == AnotherMongoDocument._id) {
    console.log('This is never true');
}

When I do a console.log of the two id's, they match exactly:

User id: 4fc67871349bb7bf6a000002 AnotherMongoDocument id: 4fc67871349bb7bf6a000002

I am assuming this is some kind of datatype problem, but I'm not sure how to convert results.userId to a datatype that will result in the above comparison being true and my outsourced brain (aka Google) has been unable to help.

mongoose node.js mongodb
9 Answers

The three possible solutions suggested here have different use cases.

  1. Use .equals when comparing ObjectId on two mongoDocuments like this
results.userId.equals(AnotherMongoDocument._id)
  1. Use .toString() when comparing a string representation of ObjectId to an ObjectId of a mongoDocument. like this
results.userId === AnotherMongoDocument._id.toString()
user_42480790

According to the above,i found three ways to solve the problem.

  1. AnotherMongoDocument._id.toString()
  2. JSON.stringify(AnotherMongoDocument._id)
  3. results.userId.equals(AnotherMongoDocument._id)
user_110936110

I faced exactly the same problem and i simply resolved the issue with the help of JSON.stringify() as follow:- 

if (JSON.stringify(results.userId) === JSON.stringify(AnotherMongoDocument._id)) {
        console.log('This is never true');
}
user_49987310
user_96857470

Here is an example that explains the issue and why it confusing for many. Only the first console log shows the object in its true form, and any other debuging/loging will be confusing because they look the same.

// Constructor for an object that has 'val' and some other stuffs
//   related to to librery...
function ID(_val) {
  this.val = _val;
  this.otherStuff = "other stuffs goes here";
}
// function to help user get usefull infos from the Object
ID.prototype.toString = function toString() {
  return `${this.val}`;
};
// Create new Object of type ID
const id = new ID('1234567');
console.log("my ID: ", id);  // my ID: Object { 
                             //    val: "1234567", 
                             //    otherStuff: "other stuffs goes here" 
                             // }

console.log("my ID: " + id); // my ID: 1234567
console.log(id === '1234567'); // false
console.log(id == '1234567'); // true
console.log(id.toString() === '1234567'); //true
console.log(`${id}` === '1234567'); // true
console.log(new ID('1234567') === id); // false
user_118762010
Related