在lodash中使用MongoDB ObjectIds

Question

I keep running into trouble when working with ObjectIds and lodash. Say I have two arrays of objects I want to use lodash _.unionBy() with:

var arr1 = [
    {
        _id: ObjectId('abc123'),
        old: 'Some property from arr1',
    },
    {
        _id: ObjectId('def456'),
        old: 'Some property from arr1',
    },
];

var arr 2 = [
    {
        _id: ObjectId('abc123'),
        new: 'I want to merge this with object in arr1',
    },
    {
        _id: ObjectId('def456'),
        new: 'I want to merge this with object in arr1',
    },
];

var res = _.unionBy(arr1, arr2, '_id');

Result

console.log(res);
/*
[
    {
        _id: ObjectId('abc123'),
        old: 'Some property from arr1',
    },
    {
        _id: ObjectId('def456'),
        old: 'Some property from arr1',
    },
    {
        _id: ObjectId('abc123'),
        new: 'I want to merge this with object in arr1',
    },
    {
        _id: ObjectId('def456'),
        new: 'I want to merge this with object in arr1',
    },
]
*/

Desired result

[
    {
        _id: ObjectId('abc123'),
        old: 'Some property from arr1',
        new: 'I want to merge this with object in arr1',
    },
    {
        _id: ObjectId('def456'),
        old: 'Some property from arr1',
        new: 'I want to merge this with object in arr1',
    },
]

Since ObjectIds are objects and they are not pointing to the same reference in many cases (eg when fetching documents from MongoDB and comparing with local seed for testing), I cannot use '_id' as iteratee.

How do I use lodash with ObjectIDs to achieve desired results?

Answer 1

Try this, I removed ObjectId because it does not work in javascript. You can use .toString for string conversion.

 var arr1 = [{ _id: 'abc123', old: 'Some property from arr1', }, { _id: 'def456', old: 'Some property from arr1', }, ]; var arr2 = [{ _id: 'abc123', new: 'I want to merge this with object in arr1', }, { _id: 'def456', new: 'I want to merge this with object in arr1', }, ]; const data = arr2.reduce((obj, ele) => { if (!obj[ele._id]) obj[ele._id] = ele.new; return obj; }, {}) arr1 = arr1.map((d) => { if (data[d._id]) { d.new = data[d._id]; } return d; }) console.log(arr1); 

Answer 2

You'll have to use _.unionWith that allows you to use a custom comparator. Use the custom comparator to check equality between the two ObjectIds:

_.unionWith(arr1, arr2, (arrVal, othVal) => arrVal._id.equals(othVal._id));

Hope it helps.

Answer 3

This is what ended up solving my problem.

var res = arr1.map(a => {
  return _.assign(a, _.find(arr2, { _id: a._id }));
});

Thanks to Tushar's answer