Question

我正在开发我的教程项目，我是实体框架的新手。

我有两个很多关系表我正在使用代码首先approuch。

这是表格定义：

 class EmployeeDBContext : DbContext
{
    public EmployeeDBContext() : base("DefaultConnection") { }
    public DbSet<Course> Courses { get; set; }
    public DbSet<Student> Students { get; set; }
}

//================================================My entities=================================================
public class Student
{
    [Key]
    public int StudentID { get; set; }
    public string StudentName { get; set; }
    public virtual ICollection<Course> Courses { get; set; }
}

public class Course
{

    [Key]
    public int CourseID { get; set; }
    public string CourseName { get; set; }
    public virtual ICollection<Student> Students { get; set; }
}

课程表包含3个科目：历史，数学，物理。

我需要添加新学生并将学生与现有课程联系起来。

知道如何实施它？

提前谢谢。

Answer 1

尝试以下代码：取决于您是否要更新courseName或添加学生列表。

     public void UpdateCourse(string courseName, List<Student> students)
        {
            var dbInstance = new EmployeeDBContext();
            Course model = (from item in dbInstance.Courses
                            where item.CourseID = courseid
                            select item);
            model.CourseName = courseName;
            foreach(var item in  students)
              {     
               var currentStudent = from stud in dbInstance.Students
                       where stud.StudentId == item.StudentId;
               if( currentStudent != null) 
                 currentStudent.Name = item.Name; 
                else
                  dbInstance.Students.Add(new Student() {.StudentId = item.StudentId, .Name = item.Name});
            }; 
            dbInstance.SaveChanges(); 
        }


 public void CreateCourse(string courseName, List<Student> students)
    {
        var model = new Course();
        model.CourseName = courseName;
        model.Students = students;
        var dbInstance = new EmployeeDBContext();
        dbInstance.Courses.Add(model); 
        dbInstance.SaveChanges();
    }

Answer 2

如果你需要创建一个学生并为他添加一门课程（或更多课程），那么使用EF的方式与用词语描述的相同......

using (var ctx= new EmployeeDBContext())
{
    // Create a new student (and set some properties)
    Student student = new Student()
    {
        StudentName = "Scott Tiger"
    };

    // Replace courseId with the course id that you need to add to the student
    student.Courses.Add(ctx.Courses.Find(courseId));
    // Add other courses if you need to

    // Let's write the student to the DB
    ctx.Students.Add(student);
    ctx.SaveChanges();

}

如何在EF多对多关系中添加新记录？

2 个答案: