Linq和SubSonic-返回嵌套的复杂类型 [英] Linq and SubSonic - returning nested complex types

问题描述

我是SubSonic的新手，也是LINQ的新手，所以我只是想将一个小应用程序组合在一起.

I'm new to SubSonic and reasonably new to LINQ as well, so I'm just trying to put a little app together.

我已经对模板进行了排序并可以正常运行，但是我在使用LINQ语句时遇到了一些麻烦(稍微简化一下，真实的语句还有其他一些联接，但是它们不会影响这个特定的问题，所以为简洁起见，我已将其删除):

I've got the templates all sorted and running okay, but I've run into a bit of trouble with this LINQ statement (simplified slightly, the real statement has some other joins but they don't affect this particular problem so I've removed them for brevity):

var addresses = from address in Database.Addresses.All()
                           select new Address()
                               {
                                   MyNestedType = new NestedType()
                                       {
                                           Field1 = address.ADDR1
                                       }
                               };

如果我执行此语句，当我尝试枚举结果时，会出现错误从'System.String'到'NestedType'的无效转换..

If I execute this statement I get the error Invalid cast from 'System.String' to 'NestedType'. when I try to enumerate the results.

我可能忽略了明显的地方，但是我看不到任何要求进行这种转换的地方.

I'm probably overlooking the obvious but I can't see anywhere that I request such a conversion.

Field1 和 address.ADDR1 都是字符串.

有什么想法我在做什么错吗?

Any ideas what I'm doing wrong?

修改:

我对此进行了另一番研究，并且为了提供更多信息，我使用SimpleRepository和一个演示该问题的SQLite数据库创建了一个小的完整示例.使用SimpleRepository，我得到的错误是不同的(序列不包含任何元素)，但是结果是相同的.这是完整的代码:

I've had another look at this and in an effort to provide more information, I've created a small, complete example using SimpleRepository and an SQLite database that demonstrates the issue. Using SimpleRepository the error I get is different (Sequence contains no elements) but the result is the same. Here's the complete code:

 public class DatabaseAddress
 {
     public int Id { get; set; }
     public string Address1 { get; set; }
 }

 public class Address
 {
     public NestedType MyNestedType;
 }

 public class NestedType
 {
     public string Field1 { get; set; }
 }

 static class Program
 {
    [STAThread]
    static void Main()
    {
         var repo = new SimpleRepository("Db", SimpleRepositoryOptions.RunMigrations);
         DatabaseAddress address1 = new DatabaseAddress();
         address1.Address1 = "Test";
         repo.Add(address1);
         var all = repo.All<DatabaseAddress>();
         var addresses = from address in repo.All<DatabaseAddress>()
                         select new Address { MyNestedType = new NestedType { Field1 = address.Address1 } };
    }
 }

在此示例中，all包含添加到数据库中的对象，但是addresses返回序列不包含任何元素".

In this example, all contains the object added to the database, but addresses returns "Sequence contains no elements".

如果我在select语句中使用匿名类型而不是具体类型，那么它将起作用.

If I use anonymous types instead of concrete types in the select statement it works.

我在这里的知识上显然有差距；任何帮助表示赞赏.

There's obviously a gap in my knowledge here; any help appreciated.

推荐答案

您必须调用ToList()，否则SubSonic提供程序将尝试使用MyNestedType进行某些操作，并且它在数据库中不存在.

You have to call ToList(), otherwise the SubSonic provider tries to do something with MyNestedType and it doesn't exist in the database.

var addresses = from address in repo.All<DatabaseAddress>().ToList()
                        select new Address { MyNestedType = new NestedType { Field1 = address.Address1 } };

更新:如果您以后再调用ToList，即:

Update: It also works if you call ToList afterwards, i.e.:

addresses.ToList().ForEach(address => Console.WriteLine("Address.MyNestedType.Field1 = {0}", address.MyNestedType.Field1));

我猜SubSonic查询提供程序中有一个错误，因为它确实适用于匿名类型，正如您提到的那样.

I guess there is a bug in the SubSonic query provider, because it does work for anonymous types, as you mentioned.

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