using string for mongodb _id

Question

I have a json document that I entered into my mongo db using the mongoimport command. I set it's _id to "MyDocId", looking at it in mongo, the _id is correctly set. in my C# code, I want to read this document using this _id:

ObjectId id = ObjectId.Parse("MyDocId");

I am getting an exception in the above code

Answer 1

You may need to use a Bson attribute on your property like so.

[BsonId]
[BsonRepresentation(BsonType.ObjectId)]
public string Id { get; set; }

There is quite a good explanation of these attributes in this answered question

BsonId vs BsonRepresentation

Answer 2

ObjectId parse will only parse strings that have a valid format . In your case, if the document's _id is a string, you don't need to parse it as an ObjectId, just use the string value in your query.

Answer 3

Since version 2.9 of MongoDB.Driver you can also use built-in convention StringIdStoredAsObjectIdConvention

        var pack = new ConventionPack
        {
            new StringIdStoredAsObjectIdConvention()
        };

        ConventionRegistry.Register("Custom Convention", pack, t => true);