Question

我有一个使用Entity Framework查询数据库的方法，并返回EF对象（ApplicationUser）。如果我有一个ApplicationUser的构造函数试图使用此方法来填充其属性，那么该对象的复杂属性是否会在设置时触发数据库的调用？在原始对象中它们是代理，因此会延迟加载，但只是将这些属性设置为同一对象的新实例的属性调用数据库？

这是一个简单的例子：

public class ApplicationUser
{
    public ApplicationUser(int userId)
    {
        ApplicationUser user = ApplicationUser.Select(userId);
        this.FirstName = user.FirstName //this is fine
        this.ApplicationRole = user.ApplicationRole //This is a complex object. Is it still going to be lazily loaded and called only if this.ApplicationRole is referenced?
    }

    public static ApplicationUser Select(int userId)
    {
        //this uses EF to return an Application User object
    }
}

Answer 1

将在此行中调用数据库：

$( ".list-group-item[data-text='Banana'] .badge" ).text(); //50

然后，您的对象将被提取，不再延迟加载。

要确保这种情况发生，您必须进行一些配置：

必须启用延迟加载和代理创建：

this.ApplicationRole = user.ApplicationRole;

导航属性必须声明为public Context() : base("YourConnectionString") { Configuration.LazyLoadingEnabled = true; Configuration.ProxyCreationEnabled = true; }：
```
virutal
```

行动中的示例

假设你有这些课程

public class ApplicationUser
{
    //...
    public virtual ApplicationRole ApplicationRole { get; set; }
    //...
}

第一击：

public class ApplicationUser
{
    public int ApplicationUserId { get; set; }
    public string FirstName { get; set; }
    public virtual ApplicationRole ApplicationRole { get; set; }

    public static Context db { get; set; }

    public ApplicationUser()
    {

    }

    public ApplicationUser(int userId)
    {
        ApplicationUser user = ApplicationUser.Select(userId);
        this.FirstName = user.FirstName; 
        this.ApplicationRole = user.ApplicationRole; //database will be hit here
    }

    public static ApplicationUser Select(int userId)
    {
        //this uses EF to return an Application User object
        return db.Users.Find(userId);
    }
}

public class ApplicationRole
{
    public int ApplicationRoleId { get; set;}
    public string Name { get; set; }
}

生成的SQL：

return db.Users.Find(userId);

Second Hit

SELECT
    [Limit1].[ApplicationUserId] AS [ApplicationUserId],
    [Limit1].[FirstName] AS [FirstName],
    [Limit1].[ApplicationRole_ApplicationRoleId] AS [ApplicationRole_Application
RoleId]
    FROM ( SELECT TOP (2)
        [Extent1].[ApplicationUserId] AS [ApplicationUserId],
        [Extent1].[FirstName] AS [FirstName],
        [Extent1].[ApplicationRole_ApplicationRoleId] AS [ApplicationRole_Applic
ationRoleId]
        FROM [dbo].[ApplicationUsers] AS [Extent1]
        WHERE [Extent1].[ApplicationUserId] = @p0
    )  AS [Limit1]

-- p0: '1' (Type = Int32)

生成SQL

this.ApplicationRole = user.ApplicationRole

如果SELECT [Extent2].[ApplicationRoleId] AS [ApplicationRoleId], [Extent2].[Name] AS [Name] FROM [dbo].[ApplicationUsers] AS [Extent1] INNER JOIN [dbo].[ApplicationRoles] AS [Extent2] ON [Extent1].[ApplicationRo le_ApplicationRoleId] = [Extent2].[ApplicationRoleId] WHERE ([Extent1].[ApplicationRole_ApplicationRoleId] IS NOT NULL) AND ([Exte nt1].[ApplicationUserId] = @EntityKeyValue1) -- EntityKeyValue1: '1' (Type = Int32, IsNullable = false)对象具有其他导航属性，它们仍然会延迟加载，没有问题。

这里有一个可能有用的提示。要查看EF何时访问数据库，请创建一个控制台应用程序，添加解决方案的引用，然后使用ApplicationRole。要查看有关日志记录的更多信息，请查看此链接https://msdn.microsoft.com/en-us/data/dn469464.aspx

设置属性时实体框架延迟加载

1 个答案: