1

我需要执行一个查询来连接两个表，按值分组，并返回组键和计数。

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;

我怎样才能使用 NHibernate 做到这一点？Message 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>

我看过其他几个问题，但没有一个完全符合这个用例（很多 GroupBy，但没有关联；很多加入，但没有 group by）

我已经开始朝两个方向前进：

// 第一次尝试

// 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>(...
4

1 回答 1

2

未测试

// 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[]>();
于 2012-08-28T13:41:22.757 回答