实体数据模型 asp.net 中的左外连接

发布于 2024-11-05 18:48:41 字数 58 浏览 0 评论 0原文

如何在 Linq to 实体框架中实现左外连接。不支持 DefaultIfEmpty 函数。请举例。

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我的黑色迷你裙 2024-11-12 18:48:41

这适用于 .NET 3.5。当您在未与 FirstorDefault 函数结合使用“from”的情况下进行连接时，它将为您提供在左侧连接表中查找的行。如果您想要多行，只需使用 where() 即可。希望这会有所帮助。

====

comments = from p in _db.Master

join t in _db.Details on p.DetailID equals t.DetailID into tg

select new 
{

 A = p.Column1,

//this next column is the one from the left joined table

 B = tg.FirstOrDefault(t => t.DetailID == p.DetailID).Column2

};

This works in .NET 3.5. When you join without doing "from" in combination with the FirstorDefault function, it will give you the row you are looking for in the left joined table. If you want multiple rows, just use where() instead.. Hope this helps.

====

comments = from p in _db.Master

join t in _db.Details on p.DetailID equals t.DetailID into tg

select new 
{

 A = p.Column1,

//this next column is the one from the left joined table

 B = tg.FirstOrDefault(t => t.DetailID == p.DetailID).Column2

};

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凹づ凸ル 2024-11-12 18:48:41

.NET 3.5 中的实体框架不提供 Linq 查询中的左联接。获取“连接记录”的方法是通过实体之间的导航属性。像这样的东西：

var query = from u in context.Users
            select new 
               {
                   User = u,
                   Orders = u.Orders.Where(...) // Filtered left join but User and Order must be related
               };

Entity framework in .NET 3.5 doesn't offer left join in Linq queries. The way to get "joined records" is through navigation property between entities. Something like:

var query = from u in context.Users
            select new 
               {
                   User = u,
                   Orders = u.Orders.Where(...) // Filtered left join but User and Order must be related
               };

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