How to Query MongoDB from Go with an Array of Object IDs?

Querying MongoDB from Go with Array of Object IDs

In MongoDB, retrieving documents based on their object identifiers stored in an array can be achieved with the $in operator and the mgo and bson packages.

Implementing the Query:

To perform the query correctly, you need to ensure that the object identifiers in the array are in the correct format. If the documents are stored with string IDs, the query you provided was accurate:

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

However, if the object identifiers are in the form of hex-encoded strings (e.g., "543d171c5b2c12420dd016"), you need to convert them to bson.ObjectId objects before using them in the query. Here's how you can do that:

<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 modification ensures that the query matches the object identifiers stored in the array as bson.ObjectId objects.

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