How to Query MongoDB from Golang using an Array of Object IDs?

Querying MongoDB from Golang Using an Array of Object IDs

In MongoDB, you can store arrays of documents, each with its own unique _id. This allows you to associate multiple documents with a parent document. When querying for these documents using Golang's mgo and bson packages, it's important to convert the _id array to the appropriate type.

Solution

If the _id values in the array are simply hex strings, the provided code is correct:

<code class="go">query := bson.M{"_id": bson.M{"$in": ids}}
c.Find(query).All()</code>

However, if the _id values are object identifiers (ObjectId), you need to convert them to the proper type:

<code class="go">oids := make([]bson.ObjectId, len(ids))
for i := range ids {
  oids[i] = bson.ObjectIdHex(ids[i])
}
query := bson.M{"_id": bson.M{"$in": oids}}</code>

This conversion is necessary because the $in operator requires an array of ObjectId values, not hex strings. By converting the hex strings to ObjectId types, you can correctly query for the documents associated with the provided _id values.

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