How to find through list of ids in MongoDB?

You can use the $in operator to find documents through a list of specific ids in MongoDB. The $in operator allows you to query multiple values in a single field, making it perfect for searching by multiple ObjectIds.

Syntax

db.collection.find({
    _id: { $in: [ObjectId("id1"), ObjectId("id2"), ObjectId("id3")] }
});

Sample Data

Let's create a collection with sample student documents ?

db.findListOfIdsDemo.insertMany([
    {"StudentName": "Carol", "StudentAge": 21},
    {"StudentName": "Bob", "StudentAge": 25},
    {"StudentName": "David", "StudentAge": 22},
    {"StudentName": "John", "StudentAge": 20},
    {"StudentName": "Mike", "StudentAge": 23}
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5c8ecadd2f684a30fbdfd575"),
        ObjectId("5c8ecae42f684a30fbdfd576"),
        ObjectId("5c8ecaed2f684a30fbdfd577"),
        ObjectId("5c8ecaf82f684a30fbdfd578"),
        ObjectId("5c8ecb092f684a30fbdfd579")
    ]
}

Display all documents from the collection ?

db.findListOfIdsDemo.find().pretty();

{
    "_id": ObjectId("5c8ecadd2f684a30fbdfd575"),
    "StudentName": "Carol",
    "StudentAge": 21
}
{
    "_id": ObjectId("5c8ecae42f684a30fbdfd576"),
    "StudentName": "Bob",
    "StudentAge": 25
}
{
    "_id": ObjectId("5c8ecaed2f684a30fbdfd577"),
    "StudentName": "David",
    "StudentAge": 22
}
{
    "_id": ObjectId("5c8ecaf82f684a30fbdfd578"),
    "StudentName": "John",
    "StudentAge": 20
}
{
    "_id": ObjectId("5c8ecb092f684a30fbdfd579"),
    "StudentName": "Mike",
    "StudentAge": 23
}

Example: Find Documents by List of IDs

To find specific documents by their ObjectIds, create an array of ID strings and convert them to ObjectIds ?

var listOfIds = ['5c8ecae42f684a30fbdfd576', '5c8ecaf82f684a30fbdfd578'];
var documentIds = listOfIds.map(function(myId) { return ObjectId(myId); });
db.findListOfIdsDemo.find({_id: {$in: documentIds }}).pretty();

{
    "_id": ObjectId("5c8ecae42f684a30fbdfd576"),
    "StudentName": "Bob",
    "StudentAge": 25
}
{
    "_id": ObjectId("5c8ecaf82f684a30fbdfd578"),
    "StudentName": "John",
    "StudentAge": 20
}

Key Points

• The $in operator matches any value in the specified array
• Convert string IDs to ObjectId() format before using in queries
• Use map() function to efficiently convert arrays of string IDs

Conclusion

The $in operator with ObjectId conversion provides an efficient way to query multiple documents by their specific IDs in MongoDB. This approach is ideal for retrieving multiple records in a single query operation.