Question

我检查了可能已有答案的问题，但似乎没有一个问题解决了我的问题：

var semesters = db.Semesters.Where(e => e.ID == semester).ToList();
var semestersbyfaculty = db.SemestersByFaculty.Where(e => e.FacultyID == id).ToList();

如何在SQL中执行以下操作，如何内部连接这两个查询：

SELECT 
   Fac.*, Sem.SemesterText
FROM 
   SemestersByFaculty AS Fac
INNER JOIN
   Semesters AS Sem
ON
   Fac.SemesterID = Sem.ID
WHERE id
   Fac.FacultyID = id

Answer 1

Inner Join

以下示例显示了一个简单的内部等值连接。

var query = from fac in db.SemesterByFaculty
            join sem in db.Semester on fac.SemesterID equals sem.ID
            where fac.FacultyID == id
            select new { Faculty = fac, SemesterText = sem.SemesterText };

有关详细信息，请参阅How to: Perform Inner Joins (C# Programming Guide)。

更新：

来自评论

模型

class MyModel {
    public MitModel.SemestersByFacul‌ty Faculty{ get; set; }
    public string SemesterText { get; set; }
}

class MyViewModel {
    public List<MyModel> SemesterFaculties { get; set; }
}

动作：

public ActionResult SomeAction(string id) {

    var query = from fac in db.SemesterByFaculty
                join sem in db.Semester on fac.SemesterID equals sem.ID
                where fac.FacultyID == id
                select new MyModel{ Faculty = fac, SemesterTest = sem.SemesterTest };

    var viewModel = new MyViewModel { SemesterFaculties = query.ToList() };
    return View(viewModel);
}

查看

@Model MyViewModel

Answer 2

假设您在SemestersByFaculty

中有以下字段

class SemestersByFaculty
{
    string FacultyName;
    int FacultyID;
    int SemesterID;
}

注意：如果您在SemestersByFaculty课程中有更多字段，则可以在以下查询中的new{}中列出这些字段：

var query = semesters.Join(semestersbyfaculty,
                                sem => sem.ID,
                                fac => fac.SemesterID,
                                (sem, fac) =>
                                    new { facName = fac.FacultyName, facId = fac.FacultyID,semText = sem.SemesterText }).Where(e=> e.fac.FacultyId = id);

现在，你拥有的是一个可以枚举的东西。您可以迭代它并检索值。它会像：

foreach (var obj in query){

   Console.writeln("{0}-{1}-{2}",obj.facName,obj.facId,obj.semText);
}

Answer 3

这是非LINQ语法的解决方案。您也可以在'db.Semesters'和'db.SemestersByFaculty'上执行'Where'过滤器，然后再将它们传递到'join'。

var result = db.SemestersByFaculty
  .Where(
    x_ => x_.FacultyID == id)
  .Join(
    db.Semesters.Where(x_ => x_.ID == semester), 
    x_ => x_.SemesterID, 
    x_ => x_.ID, 
    (x_, y_) => new 
    { 
      FacultyID = x_.ID, 
      SemesterID = y_.SemesterID,
      Sem = y_.SemesterText 
    })
  .ToList();

MVC EF - 内部加入

3 个答案:

Inner Join