Question

我有一些类似于以下的实体：

public class Teacher
{
    public int TeacherId { get; set; }
    public string TeacherName { get; set; }
    public int Age { get; set; }
    public string CurrentGrade { get; set; }
    public int YearsTeaching { get; set; }
    pubilc ICollection<StudentFeedback> StudentFeedback { get; set; }
}

public class StudentFeedback
    {
        public int StudentFeedBackId { get; set; }
        public int TeacherId { get; set; }
        public int StudentId { get; set; }
        public string Feedback { get; set; }

        public Teacher Teacher { get; set; }
        public Student Student { get; set; }
    } 
    
public class Student
{
    public int StudentId { get; set; }
    public string StudentName { get; set; }
    public int Age { get; set; }
    public string CurrentGrade { get; set; }
}

我有一个存储库，其中有一个方法，我想返回一个老师或老师列表，其中 StudentFeedback 返回的学生属于正在查看它的学生（studentId 存储在令牌中）。

所以，假设我有一个教师 (teacherId) 和一个学生 (userId) 正在访问 API 端点。我目前有以下几点：

int teacherId = 2;
int userId = 20; // This is the currently logged in user, extracted from the token.

var query = _context.Teachers.AsQueryable();/* _context is the DataContext*/
query = query.Where(t => p.TeacherId == teacherId);
query = query.Where(u => u.StudentFeedback.Any(x => x.StudentId == userId));

然而，这仍然会返回所有学生的所有学生反馈，只要用户 ID（学生）有为相关教师提供的反馈。我查看了执行的查询，问题是 studentId 谓词位于错误的位置。查询的一个非常粗略的版本是：

SELECT      *
FROM        (   SELECT  t.*
                FROM    dbo.Teachers t
                WHERE   (t.TeacherId = 2)
                        AND EXISTS (   SELECT   1
                                       FROM     dbo.StudentFeedback t0
                                       WHERE    (t.TeacherId = t0.TeacherId)
                                                AND (t0.StudentId = 20))) p
LEFT JOIN   dbo.StudentFeedback sf ON p.TeacherId = sf.TeacherId

而它应该是这样的

SELECT      *
FROM        (   SELECT  t.*
                FROM    dbo.Teachers t
                WHERE   (t.TeacherId = 2)) p
LEFT JOIN   dbo.StudentFeedback sf ON p.TeacherId = sf.TeacherId
                                      AND   sf.StudentId = 20

但我不知道如何做到这一点。我设置的 IQueryable 谓词是否有问题，或者我是否错过了数据上下文中模型构建器中的某些逻辑？谢谢。

编辑：我正在使用 Entity Framework Core 5.0.2，我也在使用 Automapper 和以下代码：

query.ProjectTo<TeacherDTO>(_mapper.ConfigurationProvider).AsNoTracking()

这是我目前返回的内容：

[
        {
            "teacherid": 2,
            "teacherName": "Jane Smith",
            "age": 35,
            "currentGrade": "One",
            "yearsTeaching": 12,
            "studentFeedback": [
                {
                    "studentFeedBackId": 12,
                    "teacherId": 6,
                    "studentId": 20,
                    "feedback": "Ms Smith is my favorite teacher"
                } ,
                {
                    "studentFeedBackId": 16,
                    "teacherId": 6,
                    "studentId": 43,
                    "feedback": "Ms Smith was so kind to me"
                } ,
                {
                    "studentFeedBackId": 21,
                    "teacherId": 6,
                    "studentId": 89,
                    "feedback": "Thank you Mrs Smith for being my teacher. I learned a lot."
                } 
            ]
        }
    ]

这是我想要回来的：

[
    {
        "teacherid": 2,
        "teacherName": "Jane Smith",
        "age": 35,
        "currentGrade": "One",
        "yearsTeaching": 12,
        "studentFeedback": [
            {
                "studentFeedBackId": 12,
                "teacherId": 6,
                "studentId": 20,
                "feedback": "Ms Smith is my favorite teacher"
            } 
        ]
    }
]

Answer 1

感谢@LucianBargaoanu 指出在映射本身中包含 where，从而为我指明了正确的方向。解决方案是在使用 Automapper 时使用 Parameterization：

此页面中的代码显示了一个示例：

string currentUserName = null;
cfg.CreateMap<Course, CourseModel>()
    .ForMember(m => m.CurrentUserName, opt => opt.MapFrom(src => currentUserName));

然后

dbContext.Courses.ProjectTo<CourseModel>(Config, new { currentUserName = Request.User.Name });

Answer 2

如果你想要加入，你应该在你的 linq 语句中使用 Join 方法。见https://www.tutorialsteacher.com/linq/linq-joining-operator-join。您得到了您在查询中所写的内容。 Where(u => u.StudentFeedback.Any(x => x.StudentId == userId)); .Any 转化为存在。

Answer 3

如果您使用 Net5 EF，您只需将一个 Students 属性添加到 Teacher 类：

public class Teacher
{
    .....
    pubilc ICollection<Student> Students { get; set; }
    pubilc ICollection<StudentFeedback> StudentFeedbacks { get; set; }
}

您可以这样使用查询：

var query = _context.Teachers.Include(i=> i.StudentFeedbacks)
.Where(t => 
t.TeacherId == teacherId 
&&  t.StudentFeedbacks.Any(x => x.StudentId == userId))
.ToArray();

IQueryable 未在实体框架核心中生成所需的查询

3 个答案: