Question

我正在使用Sql Server 2012和.NET 4

我想转换为C＃的Sql看起来像这样：

SELECT rd.Name, rd.Description, prdv.Value
FROM RoleDetail rd 
    JOIN Role r ON r.RoleID = rd.RoleID
    JOIN PersonRole pr ON pr.RoleID = r.RoleID
    LEFT OUTER JOIN PersonRoleDetailValue prdv ON prdv.RoleDetailID = rd.RoleDetailID
WHERE pr.PersonID = 42

经过多次尝试和浪费了很多时间，当我开始时，我似乎并没有好转。任何帮助表示赞赏。

我更喜欢方法语法，但查询语法解决方案也非常受欢迎。

解决方案（感谢David B的回答）

以下是两种可行的解决方案。我希望别人能受益......

方法语法：

var methodSyntax = db.PersonRoles
    .Where(pr => pr.PersonID == 42)
    .SelectMany(pr => pr.Role.RoleDetails)
    .SelectMany(rd => rd.PersonRoleDetailValues.DefaultIfEmpty(), (rd, prdv) => new
        {
            Name = rd.Name,
            Description = rd.Description,
            Value = prdv.Value
        });

查询语法：

var querySyntax = from pr in db.PersonRoles
     where pr.PersonID == 42
     let r = pr.Role
     from rd in r.RoleDetails
     from prdv in rd.PersonRoleDetailValues.DefaultIfEmpty()
     select new
     {
         Name = rd.Name,
         Description = rd.Description,
         Value = prdv.Value
     };

谢谢

Answer 1

如果映射设置正确，则类型之间应该存在导航属性。这使您可以开始查询一种类型并包含其他类型，而无需反复指定连接列。

from pr in dataContext.PersonRoles
where pr.PersonId = 42
  //navigation property Many->One  Queryable.Select
let r = pr.Role  
  //navigation property One->Many  Queryable.SelectMany
from rd in r.RoleDetails
  //navigation property One->Many, match null if none
from prdv = rd.PersonRoleDetailValues.DefaultIfEmpty()
select new
{
  Name = rd.Name,
  Description = rd.Description,
  Value = prdv.Value
}

为了好玩，方法语法尽可能简洁：

dataContext.PersonRoles
  .Where(pr => pr.PersonId = 42)
  .SelectMany(pr => pr.Role.RoleDetails)
  .SelectMany(rd => rd.PersonRoleDetailValues.DefaultIfEmpty(),
    (rd, prdv) => new
  {
    Name = rd.Name,
    Description = rd.Description,
    Value = prdv.Value
  });

从Sql到Linq-to Sql

1 个答案: