Fluent NHibernate:左外连接..AND查询

本文关键字：连接 AND 查询 NHibernate Fluent | 更新日期: 2023-09-27 18:25:00

我有下一个使用QueryOver:的Fluent NHibernate查询

IQueryOver<Task> query = session
    .QueryOver<Task>()
    .JoinAlias(x => x.Subject, () => subject, JoinType.LeftOuterJoin)
    .JoinAlias(() => subject.Localizations, () => localization, JoinType.LeftOuterJoin)
    .Where(() => localization.Language.Id == languageId || localization.Language.Id == null);
    .Where(x => x.UserId == userId)

这将执行下一个查询：

SELECT * FROM Tasks left outer join Subjects on Tasks.SubjectId = Subjects.IdAsignatura 
left outer join Languages on Subjects.SubjectId=Languages.SubjectId
WHERE Tasks.UserId = xxx 
and (Languages.LanguageId = yyy or Languages.LanguageId = is null)

我想避免最后一行使用"LEFT OUTER JOIN…AND"，如下所示：

SELECT * FROM Tasks left outer join Subjects on Tasks.SubjectId = Subjects.IdAsignatura 
left outer join Languages on Subjects.SubjectId=Languages.SubjectId AND Languages.LanguageId = yyy
WHERE Tasks.UserId = xxx

有没有一种方法可以执行"LEFT OUTER JOIN…AND"Fluent NHibernate查询？

Fluent NHibernate:左外连接..AND查询

CreateAlias有一个重载：

/// <param name="path">Lambda expression returning association path</param>
/// <param name="alias">Lambda expression returning alias reference</param>
/// <param name="joinType">Type of join</param>
/// <param name="withClause">Additional criterion for the SQL on clause</param>
/// <returns>
/// criteria instance
/// </returns>
IQueryOver<TRoot, TSubType> JoinAlias<U>(Expression<Func<U>> path
     , Expression<Func<U>> alias, JoinType joinType
     , ICriterion withClause);

这意味着，我们可以将WHRE的限制转化为ON条款

/// instead of this
.JoinAlias(() => subject.Localizations, () => localization, JoinType.LeftOuterJoin)
.Where(() => localization.Language.Id == languageId 
          || localization.Language.Id == null);
/// We can use this:
.JoinAlias(() => subject.Localizations, () => localization, JoinType.LeftOuterJoin
            // the 4th param is appended to ON clause with AND operator
            , Restrictions.Where(() => localization.Language.Id == languageId)
)

withClause可以注入SELECT的ON部分，但始终使用AND运算符。因此，它只能应用比基本映射关系更多的限制。

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