Linq to Entities 查询层次结构

Question

我有这个table:

CREATE TABLE [md].[Services]
(
    [id] [nvarchar](36) NOT NULL,
    [Value] [nvarchar](500) NOT NULL,
    [Parentid] [nvarchar](36) NULL,
    [Status] [nvarchar](10) NOT NULL
)

我写了一个查询来获得数据的扁平视图，如下所示：

SELECT
    bottomLevel.id as [Bot],
    midLevel.id as [Mid], 
    topLevel.id as [Top]
FROM
    md.Services bottomLevel
LEFT OUTER JOIN 
    md.Services midLevel ON bottomLevel.Parentid = midLevel.id
LEFT OUTER JOIN
    md.Services topLevel ON midLevel.Parentid = topLevel.id

但对于我来说，我似乎无法用 EF 找出它的 LINQ 版本。

我想到了这个，但是它 returns 行多了，我还没有弄清楚我错过了什么......有什么想法吗？

var query = (from level3 in _db.Services
             from level2 in _db.Services
                               .Where(x => x.Parentid == level3.id).DefaultIfEmpty()
             from level1 in _db.Services
                               .Where(x => x.Parentid == level2.id).DefaultIfEmpty()
             select new
                    {
                        Bot = level3.id,
                        Mid = level2.id,
                        Top = level1.id,
                    });

Answer 1

我明白了。我遗漏了一些东西，我正在倒退...

var query2 = (
                from level1 in db.ServiceTypes
                join s1 in db.ServiceTypes on level1.ParentGuid equals s1.Guid into q1
                from level2 in q1.DefaultIfEmpty()
                join s2 in db.ServiceTypes on level2.ParentGuid equals s2.Guid into q2
                from level3 in q2.DefaultIfEmpty()
                select new
                {
                    BottomGuid = level1.Guid,
                    MidGuid = level2.Guid,
                    TopGuid = level3.Guid,
                }

            );

Linq to Entities 查询层次结构

Linq to Entities query for hierarchy

.net

c#

linq

linq-to-entities

entity-framework