Querying mongodb from golang using the _id stored in an array

Question

So here is my question. I have an array which are stored the _ids of mongodbs objects. Whats the right way to retrieve them all in one query using the mgo and bson package?

So if the array is like that: ids:=["543d171c5b2c12420dd016","543d171c5b2dd016"]

How we make the query ? I tried that but I know its wrong.

query := bson.M{"_id": bson.M{"$in": ids}}
c.Find(query).All()

Thanks in advance

Toponym

Answer 1

If the documents are stored with string ids, then the code looks correct.

The ids look like hex encoded object ids. If the object identifiers are object ids, then you need to the convert the hex strings to object ids:

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

Unlimber

Answer 2

MongoDB syntax for go.mongodb.org/mongo-driver has been updated, this should work using the official driver.

oids := make([]primitive.ObjectID, len(ids))
for i := range ids {
    objID, err := primitive.ObjectIDFromHex(ids[i])
    if err == nil {
        oids = append(oids, objID)
    }
}

Sale

Answer 3

This is to convert back to a struct that can be used through out the app

type MongoUser struct {
    ID        *primitive.ObjectID `json:"id" bson:"_id"`
    FirstName string              `json:"first_name" bson:"firstName"`
    LastName  string              `json:"last_name" bson:"lastName"`
    Email     string              `json:"email" bson:"email"`
}

This is a helper method that takes your slice of ids and turns it into the object id type.

  func formatObjectIdMultiple(hex []string) ([]primitive.ObjectID, error) {
    var list []primitive.ObjectID

    oids := make([]primitive.ObjectID, len(hex))
    for _, i := range hex {
        objectId, err := primitive.ObjectIDFromHex(i)
        if err != nil {
            return nil, err
        }
        oids = append(oids, objectId)
    }
    return list, nil
}

Here is my method for the db. Its important you use bson.M for some reason bson.D does not work with this. Also dont forget to close your cursor the defer function will close it at the end of your GetMultipleUser function.

    func (mongo *Mongo) GetMultipleUser(ids []string) ([]*MongoUser, error) {

    objectIDs, err := formatObjectIdMultiple(ids)
    if err != nil {
        return nil, err
    }

    query := bson.M{"_id": bson.M{"$in": objectIDs}}

    coll := mongo.Con.Database("dbName").Collection("users")
    cursor, err := coll.Find(context.Background(), query)
    if err != nil {
        return nil, err
    }
    defer func() {
        cursor.Close(context.Background())
    }()
    var output []*MongoUser
    for cursor.Next(context.Background()) {
        var temp *MongoUser
        cursor.Decode(&temp)
        output = append(output, temp)
    }

    return output, nil
}

Andres