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

开始使用一对多

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 = 0; 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 == 1 select a).First();
                //删除子集
                var detailitem=users.detail.Where(p=>p.DetailId==7).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==2).FirstOrDefault();
                detailitem2.NAME = "这是修改后的数据";
                db.Entry(detailitem2).State = System.Data.Entity.EntityState.Modified;
                db.SaveChanges();
            }
}

然后是对多对

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");
                });

写测试方法：

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 = 20, 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