Question

我的数据库中有多对多的关系。我正在使用Entity Framework发送查询。

我的课程是Student，Course和StudentCourse。

    public IHttpActionResult Get()
    {
        var data = context.Students;

        return Ok(data);
    }

我创建了一个查询拦截器来查看发送到数据库的查询。

    Intercepted on: ReaderExecuted :-  IsAsync: False, Command Text: SELECT 
        [Extent1].[Id] AS [Id], 
        [Extent1].[Name] AS [Name]
        FROM [dbo].[Student] AS [Extent1] 
    Intercepted on: ReaderExecuted :-  IsAsync: False, Command Text: SELECT 
        [Extent1].[Id] AS [Id], 
        [Extent1].[Name] AS [Name]
        FROM [dbo].[Student] AS [Extent1] 
    Intercepted on: ReaderExecuted :-  IsAsync: False, Command Text: SELECT 
        [Extent2].[Id] AS [Id], 
        [Extent2].[Name] AS [Name]
        FROM  [dbo].[Course] AS [Extent1]
        INNER JOIN [dbo].[Courses] AS [Extent2] ON [Extent1].[CourseId] = [Extent2].[Id]
        WHERE [Extent1].[CourseId] = @EntityKeyValue1 
    Intercepted on: ReaderExecuted :-  IsAsync: False, Command Text: SELECT 
        [Extent2].[Id] AS [Id], 
        [Extent2].[Name] AS [Name]
        FROM  [dbo].[Course] AS [Extent1]
        INNER JOIN [dbo].[Courses] AS [Extent2] ON [Extent1].[CourseId] = [Extent2].[Id]
        WHERE [Extent1].[StudentId] = @EntityKeyValue1 
....
...
...

它发送14个查询以从服务器获取关系数据。这是多行数据的性能问题吗？

Answer 1

我认为你正在看到所谓的延迟加载。基本上会发生的是向db发出查询以获取所有学生。然后，当发送响应时，遍历学生集合并将StudentCourses加载到每个学生，一次一个查询。然后，当每个学生发回学生课程时，会加载课程属性（一次一个），然后发回。

您应该尝试禁用延迟加载并使用预先加载来与学生一起加载StudentCourses和Courses。像这样：

context.Students.Include(s=>s.StudentCourses).Include(s=>s.StudentCourses.Select(sc=>sc.Course)

实体框架有很多对查询的性能

1 个答案: