此处表后面的代码确实在数据库中生成了一个新的动态表。但是,我不知道如何访问它或如何通过C#代码添加到它的链接。
3NF,三张桌子。
表格:
public class Student
{
[Key, Column(Order = 1)]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int StudentID { get; set; }
public string StudentName { get; set; }
public DateTime? DateOfBirth { get; set; }
public virtual ICollection<Course> Courses { get; set; }
}
public class Course
{
[Key, Column(Order = 1)]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int CourseId { get; set; }
[Index("CourseName", 2, IsUnique = true)]
public string CourseName { get; set; }
public virtual ICollection<Student> Students { get; set; }
}
DBContext.cs
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<Student>()
.HasMany<Course>(s => s.Courses)
.WithMany(c => c.Students)
.Map(cs =>
{
cs.MapLeftKey("FK_StudentID");
cs.MapRightKey("FK_CourseID");
cs.ToTable("StudentCourse");
});
}
上面的代码在这里创建了一个像这样的表:
StudentCourse
=================================
| FK_StudentID | FK_CourseID |
=================================
编辑:我现在正在看这个问题, 如何通过Fluent API实体框架定义多对多关系?
编辑,澄清: 很抱歉,我的延迟:这与何时(例如您已经有学生或单独添加学生)更相关。但是,然后要动态地将它们连接到一个或多个课程。同样,您添加新课程。但是,这些可以由学生采取。
但是,我不知道如何访问它或如何通过C#代码添加到它的链接。
在EF6中,您不能直接访问它。而是只需将项目添加/删除到Student.Courses
或Course.Students
导航属性。
例如
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using System.Data.Entity;
namespace Ef6Test
{
public class Student
{
[Key, Column(Order = 1)]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int StudentID { get; set; }
public string StudentName { get; set; }
public DateTime? DateOfBirth { get; set; }
public virtual ICollection<Course> Courses { get; } = new HashSet<Course>();
}
public class Course
{
[Key, Column(Order = 1)]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int CourseId { get; set; }
[Index("CourseName", 2, IsUnique = true)]
[StringLength(100)]
public string CourseName { get; set; }
public virtual ICollection<Student> Students { get; } = new HashSet<Student>();
}
public class TestContext : DbContext
{
public DbSet<Student> Students { get; set; }
public DbSet<Course> Courses { get; set; }
}
internal class Program
{
public static void Main(string[] args)
{
using (var db = new TestContext())
{
db.Database.Log = m => Console.WriteLine(m);
if (db.Database.Exists())
db.Database.Delete();
db.Database.Create();
var s = new Student();
db.Students.Add(s);
s.Courses.Add(new Course());
db.SaveChanges();
}
}
}
}
输出
Started transaction at 1/6/2021 11:52:17 AM -06:00
INSERT [dbo].[Courses]([CourseName])
VALUES (NULL)
SELECT [CourseId]
FROM [dbo].[Courses]
WHERE @@ROWCOUNT > 0 AND [CourseId] = scope_identity()
-- Executing at 1/6/2021 11:52:17 AM -06:00
-- Completed in 9 ms with result: SqlDataReader
INSERT [dbo].[Students]([StudentName], [DateOfBirth])
VALUES (NULL, NULL)
SELECT [StudentID]
FROM [dbo].[Students]
WHERE @@ROWCOUNT > 0 AND [StudentID] = scope_identity()
-- Executing at 1/6/2021 11:52:17 AM -06:00
-- Completed in 7 ms with result: SqlDataReader
INSERT [dbo].[StudentCourses]([Student_StudentID], [Course_CourseId])
VALUES (@0, @1)
-- @0: '1' (Type = Int32)
-- @1: '1' (Type = Int32)
-- Executing at 1/6/2021 11:52:17 AM -06:00
-- Completed in 17 ms with result: 1
Committed transaction at 1/6/2021 11:52:17 AM -06:00
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