NHibernate Group By Many-to-Many Association

Question

我需要执行一个连接两个表的查询，按值分组，并返回组密钥和计数。

CREATE TABLE Message(
    ID INT NOT NULL 
, Note NVARCHAR(128)); 

CREATE TABLE Message_Users(
    MessageID INT NOT NULL 
, UserID NVARCHAR(128) NOT NULL); 

我需要执行这个查询：

SELECT mu.UserID, COUNT(m.ID) 
FROM Message m 
JOIN Message_Users mu 
    ON m.ID = mu.MessageID 
GROUP BY mu.UserID; 

我怎样才能做到这一点使用NHibernate的？消息表映射如下：

<?xml version="1.0" encoding="utf-8" ?> 
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="DataModel" namespace="DataModel.Message"> 
    <class name="Message" table="Message"> 
    <id name="ID"> 
     <generator class="native" /> 
    </id> 
    <bag name="AssociatedUsers" table="Message_Users" lazy="false"> 
     <key column="MessageID" /> 
     <element column="UserID" type="System.String" /> 
    </bag> 
    </class> 
</hibernate-mapping> 

我已经看过其他一些问题，但没有达到相当这个用例（大量的GroupBy的，但不能与关联; plenty of join, but not with a group by）

两个方向我已经开始准备：

//首先尝试

// Doesn't work as message.AssociatedUsers is a collection, so mu.Key is actually a collection 
var query = transactionContext.Session.Query<Message>();  
var r = from message in query 
     group message by message.AssociatedUsers into mu 
     select new {UserID = mu.Key, Count = mu.Count()}; 

//第二次尝试

var query = transactionContext.Session.QueryOver<Message>(); 
var join = query.Right.JoinQueryOver<string>(_message => _message.AssociatedUsers); 
var select = join.Select(
     // Select generic parameter doesn't seem to be related to the type of the join (<Message, string>) 
    Projections.Group<string>(... 

Answer 1

没有测试

// Option 1 
var r = from message in Session.Query<Message>() 
     from userid in message.AssociatedUsers 
     group userid by userid into g 
     select new { UserID = g.Key, Count = g.Count() }; 

// Option 2 
string userId = null; 
var r = Session.QueryOver<Message>() 
    .JoinQueryOver<string>(m => m.AssociatedUsers,() => userId) 
    .SelectList(list => list 
     .SelectGroup(() => userid) 
     .Select(Projections.Count())) 
    .List<object[]>();