Question

将正常的SQL查询转换为涉及多个LEFT OUTER JOINS的LINQ查询而苦苦挣扎..

原始SQL查询：

SELECT a.*
FROM Testers t
LEFT OUTER JOIN Users u ON u.TesterId = t.TesterId
LEFT OUTER JOIN ValidForms v ON v.DepartmentId = u.DepartmentId

LINQ查询代码如下：

var x = (from t in Context.Testers.AsEnumerable()
         from u in Context.Users
                    .Where(a => a.TesterId == t.TesterId)
                    .DefaultIfEmpty()
                 from v in Context.ValidForms
                  .Where(b => b.DepartmentId == u.DepartmentId)
                    .DefaultIfEmpty()
                    Select new myEntity
                    {
                      col1 = t.col1,
                        col2 = t.col2
                    }).AsEnumerable()

return x.ToList();

运行查询，我收到错误：非静态方法需要目标

感谢是否有人可以在LINQ中指出如何正确地进行查询。

我还检查了此处发布的SO问题，但我无法理解所提供的概念：SQL to Linq query with multiple left outer joins

感谢。

更新：我从SO question得到了这个。

Answer 1

This is a good way to do it.如果您遵循该示例，您的代码应如下所示：

var x = (from t in Context.Testers.AsEnumerable()
         join u in Context.Users on t.TesterId equals u.TesterId into group1
         from a in group1.DefaultIfEmpty()
         join v in Context.ValidForms on a.DepartmentId equals v.DepartmentId into group2
         from b in group2.DefaultIfEmpty()
         select new MyEntity {
             col1 = b.col1,
             col2 = b.col2
         }).AsEnumerable();

<强>已更新

var x = (from t in Context.Testers.AsEnumerable()
         join u in Context.Users on t.TesterId equals u.TesterId 
         join v in Context.ValidForms on u.DepartmentId equals v.DepartmentId into group1
         from b in group1.DefaultIfEmpty()
         select new MyEntity {
             col1 = (b != null) ? b.col1 : null,
             col2 = (b != null) ? b.col2 : null
         }).AsEnumerable();

将具有多个左外部联接的SQL查询转换为LINQ查询

1 个答案: