3

我在 SQLite 数据库上有实体框架 4 模型。模型的一部分看起来像这样 在此处输入图像描述

所有 Id 字段都具有 Guid 类型（SQLite 表 DDL 中的唯一标识符）。但是当我运行以下 LINQ 查询时，我得到了异常。

var query = AbonentPfrs.Select(a => 
    new 
    {
        AbPfr = a,
        Pfr = a.PfrCertificates.Select(c => c.Id), 
        Ac = a.AcCertificates.Select(c => c.Id)
    }
);
query.ToList();

当我运行它时，我得到

System.InvalidOperationException: The type of the key field 'Id' is expected to be 'System.Guid', but the value provided is actually of type 'System.String'.

更新：我发现 EF 生成的 SQL 查询真正返回字符串作为其中一个实体的标识符。

进入数据库的 SQL((query as ObjectQuery).ToTraceString())如下所示：

SELECT 
[UnionAll1].[C2] AS [C1], 
[UnionAll1].[C3] AS [C2], 
[UnionAll1].[Id] AS [C3], 
[UnionAll1].[PfrRegNumber] AS [C4], 
[UnionAll1].[PfrUnitId] AS [C5], 
[UnionAll1].[Account_Id] AS [C6], 
[UnionAll1].[ActiveCertificate_Id] AS [C7], 
[UnionAll1].[C1] AS [C8], 
[UnionAll1].[Id1] AS [C9], 
[UnionAll1].[C4] AS [C10]
FROM  (SELECT 
  CASE WHEN ([Extent2].[Id] IS NULL) THEN NULL ELSE 1 END AS [C1], 
  1 AS [C2], 
  1 AS [C3], 
  [Extent1].[Id] AS [Id], 
  [Extent1].[PfrRegNumber] AS [PfrRegNumber], 
  [Extent1].[PfrUnitId] AS [PfrUnitId], 
  [Extent1].[Account_Id] AS [Account_Id], 
  [Extent1].[ActiveCertificate_Id] AS [ActiveCertificate_Id], 
  [Extent2].[Id] AS [Id1], 
  NULL AS [C4]
  FROM  [AbonentPfrs] AS [Extent1]
  LEFT OUTER JOIN [Certificates] AS [Extent2] ON [Extent1].[Id] = [Extent2].[AbonentPfr_PfrCertificates_Certificate_Id]
UNION ALL
  SELECT 
  2 AS [C1], 
  2 AS [C2], 
  2 AS [C3], 
  [Extent3].[Id] AS [Id], 
  [Extent3].[PfrRegNumber] AS [PfrRegNumber], 
  [Extent3].[PfrUnitId] AS [PfrUnitId], 
  [Extent3].[Account_Id] AS [Account_Id], 
  [Extent3].[ActiveCertificate_Id] AS [ActiveCertificate_Id], 
  NULL AS [C4], 
  [Extent4].[Id] AS [Id1]
  FROM  [AbonentPfrs] AS [Extent3]
  INNER JOIN [Certificates] AS [Extent4] ON [Extent3].[Id] = [Extent4].[AbonentPfr_AcCertificates_Certificate_Id]) AS [UnionAll1]
ORDER BY [UnionAll1].[Id] ASC, [UnionAll1].[C1] ASC

在此处输入图像描述

最后一列是证书实体的 ID。但最后一个有类型 Guid 和前一个 - 字符串。如果我单独运行部分查询，那么我会得到下一个列类型（最后两个）：

  1. 首先选择：Guid、Object
  2. 第二个选择：对象，Guid
  3. 联合所有：Guid、Object
  4. 外选：String、Guid

为什么外部选择在最后一列中返回字符串？

4

2 回答 2

0

执行外连接时，当查询遇到缺失值时，该行将CASE WHEN ([Extent2].[Id] IS NULL) THEN NULL ELSE 1 END AS [C1]返回空值。C1在 .NET 中，GUID 是一种值类型（128 位整数），因此不能在不跳过箍的情况下将其设置为 null。（有关 GUID 结构的可空性的更多信息，请参阅为什么没有 Guid.IsNullOrEmpty() 方法。）

由于返回的值可以为空并且格式为 xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx，因此假定为字符串。

于 2013-07-03T23:14:35.690 回答
0

似乎顺序是重点。没有排序最后两列的结果类型是 Guid 和 Objects。订购 - 字符串和指导。两个订单表达式都取决于[Extent2].[Id]列。SQLite 不操作 Guid 类型，所以我认为值被转换为字符串。这是 EF4 和 System.Data.SQLite 集成的难点之一。所以我需要找到一种方法来强制 EF 不生成排序子句......

于 2013-07-04T08:41:16.483 回答