Question

我们正在研究Entity Framework中的延迟加载和紧急加载之间的区别。我们正在寻找该实体创建的SQL查询。我们有这样的省模型：

public class Province
{
    [Key]
    public int Id { get; set; }

    [Required]
    [MaxLength(150)]
    public string Name { get; set; }

    public int CountryId { get; set; }

    public virtual Country Country { get; set; }
    public virtual IList<City> City { get; set; }
}

如果我们使用急切加载，并且我们希望国家/地区属性和城市属性充满数据，那么实体将创建并像这样进行SQL查询（我们使用 .include（“ PropertyName or Expression “）加载国家和城市）：

SELECT 
[Project1].[Id] AS [Id], 
[Project1].[Name] AS [Name], 
[Project1].[CountryId] AS [CountryId], 
[Project1].[Id1] AS [Id1], 
[Project1].[Name1] AS [Name1], 
[Project1].[C1] AS [C1], 
[Project1].[Id2] AS [Id2], 
[Project1].[Name2] AS [Name2], 
[Project1].[ProvinceId] AS [ProvinceId]
FROM ( SELECT 
    [Extent1].[Id] AS [Id], 
    [Extent1].[Name] AS [Name], 
    [Extent1].[CountryId] AS [CountryId], 
    [Extent2].[Id] AS [Id1], 
    [Extent2].[Name] AS [Name1], 
    [Extent3].[Id] AS [Id2], 
    [Extent3].[Name] AS [Name2], 
    [Extent3].[ProvinceId] AS [ProvinceId], 
    CASE WHEN ([Extent3].[Id] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C1]
    FROM   [dbo].[Province] AS [Extent1]
    INNER JOIN [dbo].[Country] AS [Extent2] ON [Extent1].[CountryId] = [Extent2].[Id]
    LEFT OUTER JOIN [dbo].[City] AS [Extent3] ON [Extent1].[Id] = [Extent3].[ProvinceId]
)  AS [Project1]
ORDER BY [Project1].[Id] ASC, [Project1].[Id1] ASC, [Project1].[C1] ASC

，当我们使用延迟加载时，它会生成SQL查询，如下所示：

SELECT 
[Extent1].[Id] AS [Id], 
[Extent1].[Name] AS [Name], 
[Extent1].[CountryId] AS [CountryId]
    FROM [dbo].[Province] AS [Extent1]

，我们仍然可以访问该省的国家和城市。我的问题是如何在不使用SQL Query的情况下延迟加载来填充国家和城市属性？（在两种情况下，我们都使用Visual Studio和SQL Profiler来获取SQL Query）

延迟加载无需SQL查询即可加载导航属性？

0 个答案: