Question

我的一个项目的配置出现问题，SQL EF正在生成似乎显示出一些意外的（至少对我来说）嵌套。这个问题有点啰嗦，但请耐心等待。

所以，说我有以下设置：

public class Order
{
    public int Id { get; set; }
    public decimal Amount { get; set; }
    public Address ShippingAddress { get; set; }
}

public class Person
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public Address Address { get; set; }
}

public class Address
{
    public int Id { get; set; }
    public string StreetAddress { get; set; }
    public string City { get; set; }
    public string State { get; set; }
    public string ZipCode { get; set; }
}

将实体配置为：

public class OrderConfiguration : EntityTypeConfiguration<Order>
{
    public OrderConfiguration()
    {
        ToTable("Orders");

        HasRequired(order => order.ShippingAddress)
            .WithRequiredDependent()
            .Map(mapping => mapping.MapKey("ShippingAddressId"));
    }
}

public class PersonConfiguration : EntityTypeConfiguration<Person>
{
    public PersonConfiguration()
    {
        ToTable("Persons");

        HasRequired(person => person.Address)
            .WithRequiredDependent()
            .Map(mapping => mapping.MapKey("AddressId"));
    }
}

我的目标是获取包含地址的订单，因此我运行一个简单的查询，例如：

var orders = context.Orders
    .Include(order => order.ShippingAddress)
    .Where(order => order.ShippingAddress.State == "FL")
    .ToList();

当我监视SQL事件探查器时，我希望看到生成的SQL从Orders表中选择并在Address表上进行内部连接

 SELECT * FROM [dbo].[Orders] AS [Extent1] 
     INNER JOIN [dbo].[Addresses] AS [Extent2] ON [Extent1].[AddressId] = [Extentd2].[Id]
     WHERE [Extent2].[State] == 'FL'

相反，我发现这是生成的：

SELECT 
[Extent1].[Id] AS [Id], 
[Extent1].[Amount] AS [Amount], 
[Join5].[Id1] AS [Id1], 
[Join5].[StreetAddress] AS [StreetAddress], 
[Join5].[City] AS [City], 
[Join5].[State] AS [State], 
[Join5].[ZipCode] AS [ZipCode], 
[Join8].[Id2] AS [Id2], 
[Join11].[Id3] AS [Id3]
FROM     [dbo].[Orders] AS [Extent1]
INNER JOIN  (SELECT [Extent2].[State] AS [State], [Extent3].[Id] AS [Id4]
    FROM   [dbo].[Addresses] AS [Extent2]
    LEFT OUTER JOIN [dbo].[Orders] AS [Extent3] ON [Extent2].[Id] = [Extent3].[ShippingAddressId]
    LEFT OUTER JOIN [dbo].[Persons] AS [Extent4] ON [Extent2].[Id] = [Extent4].[AddressId] ) AS [Join2] ON [Extent1].[Id] = [Join2].[Id4]
LEFT OUTER JOIN  (SELECT [Extent5].[Id] AS [Id1], [Extent5].[StreetAddress] AS [StreetAddress], [Extent5].[City] AS [City], [Extent5].[State] AS [State], [Extent5].[ZipCode] AS [ZipCode], [Extent6].[Id] AS [Id5]
    FROM   [dbo].[Addresses] AS [Extent5]
    LEFT OUTER JOIN [dbo].[Orders] AS [Extent6] ON [Extent5].[Id] = [Extent6].[ShippingAddressId]
    LEFT OUTER JOIN [dbo].[Persons] AS [Extent7] ON [Extent5].[Id] = [Extent7].[AddressId] ) AS [Join5] ON [Extent1].[Id] = [Join5].[Id5]
LEFT OUTER JOIN  (SELECT [Extent9].[Id] AS [Id2]
    FROM   [dbo].[Addresses] AS [Extent8]
    LEFT OUTER JOIN [dbo].[Orders] AS [Extent9] ON [Extent8].[Id] = [Extent9].[ShippingAddressId]
    LEFT OUTER JOIN [dbo].[Persons] AS [Extent10] ON [Extent8].[Id] = [Extent10].[AddressId] ) AS [Join8] ON [Extent1].[Id] = [Join8].[Id2]
LEFT OUTER JOIN  (SELECT [Extent12].[Id] AS [Id6], [Extent13].[Id] AS [Id3]
    FROM   [dbo].[Addresses] AS [Extent11]
    LEFT OUTER JOIN [dbo].[Orders] AS [Extent12] ON [Extent11].[Id] = [Extent12].[ShippingAddressId]
    LEFT OUTER JOIN [dbo].[Persons] AS [Extent13] ON [Extent11].[Id] = [Extent13].[AddressId] ) AS [Join11] ON [Extent1].[Id] = [Join11].[Id6]
WHERE N'FL' = [Join2].[State]

显然，这比需要做的工作要多得多。是否有更简单的方法来执行此操作或我是否正确配置了实体？我不明白为什么它会撤回所有这些额外的连接，或者我如何将它们限制在我当时需要的表格中。任何见解都会非常感激！

谢谢，德里克

Answer 1

正如您所注意到的，.Include()有时会产生可怕的SQL！

我发现在这种情况下最简单的解决方案是在初始加载后直接显式加载所需的相关实体。这方面的缺点是额外的数据库调用 - 它将为每个订单调用一次。

var orders = (
    from order in context.Orders
    where order.ShippingAddress.State == "FL"
    select order)
    .ToList();

var t1 = (
    from order in orders
    from address in order.ShippingAddress
    select address)
    .ToList();

EF减少嵌套类型的外部联接

1 个答案: