NHibernate JoinQueryOver returns all subtype entries - nhibernate

Question

I know there are many similar topics but I couldn't find the answer I am searching for.
I have Message with list of Receivers. I am trying to get all messages with state new and receivers of type A. I get all messages having corresponding receivers but with all of their receivers. I only want to get the receivers I am interested in.
Here is what I am trying to use:
var messages = session.QueryOver<MessageDTO>()
.Where(message => message.State == MessageState.New)
.JoinQueryOver<MessageReceiverDTO>(message => message.MessageReceivers)
.Where(receiver => receiver.Type == ReceiverType.A)
.TransformUsing(Transformers.DistinctRootEntity)
.List();
//.Where(message => message.MessageReceivers.Count > 0)
//.ToList();
Would be great to have help with that. I also tried using Select for getting message and receiver out of the query but that didn't work neither.

Answer 1

Try QueryOver with alias:
MessageDTO messageAlias = null;
MessageReceiverDTO receiverAlias = null;
var query =
session.QueryOver<MessageDTO>(() => messageAlias)
.JoinAlias(() => messageAlias.Receivers, () => receiverAlias)
.Where(() => messageAlias.State == MessageState.New)
.And(() => receiverAlias.Type == ReceiverType.A);

Answer 2

I think Transformers.AliasToEntityMap might be useful here. Basically it transforms each row in your resulting query to an IDictionary with keys corresponding to alias names and values corresponding to entities. For example:
MessageDTO message = null;
MessageReceiverDTO receiver = null;
var messages = session.QueryOver<MessageDTO>(() => messageAlias)
.Where(message => message.State == MessageState.New)
.JoinQueryOver<MessageReceiverDTO>(message => message.MessageReceivers, () => receiver)
.Where(receiver => receiver.Type == ReceiverType.A)
.TransformUsing(Transformers.AliasToEntityMap)
.List<IDictionary>();
MessageDTO firstMessage = (MessageDTO)messages[0]["message"];
MessageReceiverDTO firstReceiver = (MessageReceiverDTO)messages[0]["receiver"];