As of v2.23.0, Expressions accessing Dictionary.Keys are no longer supported via IndexKeysDefinitionBuilder

We are trying to update to the latest Mongo C# Driver to use the new EntityFramework lib, but haven’t been able to get past a breaking change that was bug (or perhaps a bug that was introduce) in v2.23.0. In v2.22.0 and prior, we have been able to pass Dictionary.Keys in an Expression via IndexKeysDefinitionBuilder. For example:

public class Thing
{
  [BsonRepresentation(BsonType.ObjectId)]
  [BsonIgnoreIfDefault]
  public string Id { get; set; }
  public string Name { get; set; }
  public Dictionary<string,string> Attributes { get; set; }
}

// Given the following

protected static IndexKeysDefinitionBuilder<TEntity> Index => Builders<TEntity>.IndexKeys;

// Some data layer code that builds indexes

var collection = database.GetCollection<Thing>("things");

await collection.Indexes.CreateOneAsync(
  new CreateIndexModel<Thing>(
    Index.Combine(
      Index.Ascending(o => o.Name),
      Index.Ascending(o => o.Attributes.Keys))));

Is there a different way to build this Expression now or was this a bug that got introduced? Any guidance is appreciated.

Hey @Rishit_Bhatia,

Our code expects to index all of the keys in the target Dictionary; it sounds like maybe it isn’t doing what we expect today. Also, in v2.23.0, we do see an invalid expression exception that gets thrown.

From what I understand about wildcard indexes, they cannot be combined with other fields without the wildcardProjection. Is that true? In other words, how would I achieve my example above with Name added ascending and Attributes added as wildcard?

Thanks in advance for your help

Perhaps something like:

// Given the following
protected static ProjectionDefinitionBuilder<TEntity> Projection => Builders<TEntity>.Projection;

var collection = database.GetCollection<Thing>("things");

await collection.Indexes.CreateOneAsync(
  new CreateIndexModel<Thing>(
    Index.Wildcard(), new CreateIndexOptions<Thing> {
      WildcardProjection = Projection.Combine(
        Projection.Include(o => o.Id),
        Projection.Include(o => o.Name),
        Projection.Include(o => o.Attributes))
    }));