NHibernate-左联接 [英] NHibernate - Left joins

问题描述

我有以下两个表:

职位，区域ID，职位编号(复合键)

Jobs AreaID, JobNo (composite key)

日志，LogID，AreaID，JobNo

Logs LogID, AreaID, JobNo

我需要获取没有任何与其关联的日志的所有作业.在SQL中，我可以这样做:

I need to get all jobs that don't have any logs associated with them. In SQL I could do:

SELECT Jobs.AreaID,
       Jobs.JobNo
FROM   Jobs
       LEFT JOIN Logs
           ON Jobs.AreaID = Logs.AreaID
           AND Jobs.JobNo = Logs.JobNo
WHERE  Logs.LogID is null

但是我不确定如何使用NHibernate做到这一点.谁能提供任何指针?

But I'm not sure how to accomplish this with NHibernate. Could anyone offer any pointers?

这是我的映射:

<class name="Job" table="Jobs">
    <composite-key name="Id">
        <key-property name="JobNo"/>
        <key-many-to-one name="Area" class="Area" column="AreaID"/>
    </composite-key>
</class>

<class name="Log" table="Logs">
    <id name="Id" column="LogID">
        <generator class="identity"/>
    </id>
    <property name="JobNo"/>
    <many-to-one name="Area" class="Area" column="AreaID"/>
</class>

谢谢

更新

好的，我稍微修改了Nosila的答案，现在这就是我想要的:

OK, I modified Nosila's answer slightly, and this is now doing what I wanted:

Log logs = null;

return session.QueryOver<Job>()
    .Left.JoinAlias(x => x.Logs, () => logs)
    .Where(x => logs.Id == null)
    .List<Job>();

我还必须将其添加到我的工作映射中:

I also had to add this to my Job mapping:

<bag name="Logs">
    <key>
        <column name="JobNo"></column>
        <column name="DivisionID"></column>
    </key>
    <one-to-many class="Log"/>
</bag>

感谢您的帮助. :)

推荐答案

我不熟悉复合标识符，因为我不使用它们，因此，我所知道的所有NHibernate都会自动创建正确的左联接.尽管如此，下面的(未经测试的)查询应该可以帮助您入门.

I'm not familiar with composite identifiers as I don't use them so for all I know NHibernate will automatically create the proper left join. None the less, the (non-tested) query below should get you started.

Job jobAlias = null;
Log logAlias = null;
YourDto yourDto = null;

session.QueryOver<Job>()
    // Here is where we set what columns we want to project (e.g. select)
    .SelectList(x => x
        .Select(x => x.AreaID).WithAlias(() => jobAlias.AreaID)
        .Select(x => x.JobNo).WithAlias(() => jobAlias.JobNo)
    )
    .Left.JoinAlias(x => x.Logs, () => logAlias, x.JobNo == logAlias.JobNo)
    .Where(() => logAlias.LogID == null)
    // This is where NHibernate will transform what you have in your `SelectList()` to a list of objects
    .TransformUsing(Transformers.AliasToBean<YourDto>())
    .List<YourDto>();

public class YourDto
{
    public int AreaID { get; set; }
    public int JobNo { get; set; }
}

注意:您需要NHibernate 3.2才能设置连接条件.

Note: You need NHibernate 3.2 in order to set join conditions.

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