api - IQueryable 未在实体框架核心中生成所需的查询
问题描述
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,其中我想要返回一个教师或教师列表,返回的 StudentFeedback 属于正在查看它的学生(studentId 存储在令牌中)。
因此,假设我有一个正在访问 API 端点的教师 (teacherId) 和一个学生 (userId)。我目前有以下内容:
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));
但是,这仍然会返回所有学生的所有 StudentFeedback,只要 userId(学生)为相关教师提供了反馈。我查看了执行的查询,问题是 studentId 谓词在错误的位置。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,或者我错过了数据上下文中模型构建器中的一些逻辑?谢谢。
编辑:我正在使用 Entity Framework Core 5.0.2,并且我也在使用 Automapper,代码如下:
query.ProjectTo<TeacherDTO>(_mapper.ConfigurationProvider).AsNoTracking()
这是我目前正在返回的内容:
[
{
"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"
}
]
}
]
解决方案
感谢@LucianBargaoanu 通过说要where
在映射本身中为我指明正确的方向。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));
接着
dbContext.Courses.ProjectTo<CourseModel>(Config, new { currentUserName = Request.User.Name });
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