EF初级入门 (一对多、多对多)

1、创建新项目并引入Entity Framework

然后就可以开始使用EF了

2、使用一对多

Users 用户类，UserDetail用户详情类：一个用户对应多个详情(仅用于测试)

 public class UserDetail
     {
         public int DetailId { get; set; }
         public string NAME { get; set; }
         public int uid { get; set; }
         public string remark { get; set; }
         public virtual Users user { get; set; }
     }
     public class Users
     {
         public int id { get; set; }
         public string Name { get; set; }
         public int Age { get; set; }
         public DateTime Birth { get; set; }
         public virtual ICollection<UserDetail> detail { get; set; }

     }

ObjectContext类：

 public class ObjectContext : DbContext
     {
         public ObjectContext()
             : base("server=.;uid=xx;pwd=xxx;database=XXX")
         {

         }
         protected override void OnModelCreating(DbModelBuilder modelBuilder)
         {
             base.OnModelCreating(modelBuilder);
             modelBuilder.Entity<Users>().HasKey(p => p.id);
             modelBuilder.Entity<UserDetail>().ToTable("UserDetail");
             modelBuilder.Entity<UserDetail>().HasKey(p => p.DetailId);
             modelBuilder.Entity<UserDetail>().Property(p => p.NAME).HasColumnName("NAME");
             modelBuilder.Entity<UserDetail>().HasRequired(p => p.user).WithMany(p => p.detail).HasForeignKey(p => p.uid);
         }
         public DbSet<Users> users { get; set; }
         public DbSet<UserDetail> userdetail { get; set; }

     }

查询方法：

 public void GetAll()
         {
             using (ObjectContext db = new ObjectContext())
             {
                 var users = (from a in db.users select a).ToList<Users>();
                 for (int i = ; i < users.Count; i++)
                 {
                     Console.WriteLine("ID:"+users[i].id+",Name:"+users[i].Name);
                     foreach (var item in users[i].detail)
                     {
                         Console.WriteLine("  id:" + item.DetailId + ",NAME" + item.NAME);
                     }
                 }
             }
         }

删除和修改子集同时进行方法

 public void Update()
 {
 using (ObjectContext db = new ObjectContext())
             {
                 var users = (from a in db.users where a.id ==  select a).First();
                 //删除子集
                 var detailitem=users.detail.Where(p=>p.DetailId==).FirstOrDefault();
                 db.Entry(detailitem).State = System.Data.Entity.EntityState.Deleted;
                 users.detail.Remove(detailitem);
                 //修改子集
                 var detailitem2 = users.detail.Where(p=>p.DetailId==).FirstOrDefault();
                 detailitem2.NAME = "这是修改后的数据";
                 db.Entry(detailitem2).State = System.Data.Entity.EntityState.Modified;
                 db.SaveChanges();
             }
 }

3、使用多对多

新增一个角色类 Roles

 public class Roles
     {
         public Roles()
         {
             users = new HashSet<Users>();
         }
         public int RoleID { get; set; }
         public string RoleName { get; set; }
         public string Remark { get; set; }
         public virtual ICollection<Users> users { get; set; }
     }

修改ObjectContext类：

 modelBuilder.Entity<Roles>().HasKey(p => p.RoleID);
             //modelBuilder.Entity<UserRoles>().HasKey(p => p.ID);
             modelBuilder.Entity<Roles>().HasMany(p => p.users).WithMany(p => p.roles).Map(
                 p =>
                 {
                     p.MapLeftKey("RoleId");
                     p.MapRightKey("UserId");
                     p.ToTable("UserRoles");
                 });

4、测试方法：

 public static void AddUserRole()
         {
             using (ObjectContext db = new ObjectContext())
             {
                 //添加一个用户 两个角色
                 var user = new Users() { Name = "Test用户1", Age = , Birth = DateTime.Now };
                 var role1 = new Roles() { RoleName = "Test角色1" };
                 var role2 = new Roles() { RoleName = "Test角色2" };
                 user.roles.Add(role1);
                 user.roles.Add(role2);
                 db.users.Add(user);
                 db.SaveChanges();
             }
         }

查询：

 public static void GetAllUserRoles()
         {
             using (ObjectContext db = new ObjectContext())
             {
                 var users = (from a in db.users select a).ToList<Users>();
                 if (users != null)
                 {
                     Console.WriteLine("User查询结果:");
                     foreach (var item in users)
                     {
                         Console.WriteLine("UserID：" + item.id + ",UserName：" + item.Name + ",Birth：" + item.Birth);
                         if (item.roles != null)
                         {
                             foreach (var role in item.roles)
                             {
                                 Console.WriteLine("  RoleId：" + role.RoleID + ",RoleNmae：" + role.RoleName + ",UserId：" + item.id);
                             }
                         }
                     }
                 }
                 var roles = (from a in db.roles select a).ToList<Roles>();
                 if (roles != null)
                 {
                     Console.WriteLine("Role查询结果:");
                     foreach (var item in roles)
                     {
                         Console.WriteLine("RoleID：" + item.RoleID + ",RoleName：" + item.RoleName);
                         if (item.users != null)
                         {
                             foreach (var user in item.users)
                             {
                                 Console.WriteLine("  UserID：" + user.id + ",UserName：" + user.Name + ",Birth：" + user.Birth + ",RoleID：" + item.RoleID);
                             }
                         }
                     }
                 }
             }
         }

然后写完测试。。。

源代码：EFDemo