C# EntityFramework延迟加载不起作用
我是EntityFramework6的新手,在POCO中不断遇到问题 下面是我的代码 Domain.csC# EntityFramework延迟加载不起作用,c#,entity-framework,C#,Entity Framework,我是EntityFramework6的新手,在POCO中不断遇到问题 下面是我的代码 Domain.cs public abstract class BaseEntity { [Key] public long Id { get; set; } } public class User : BaseEntity { public long UserRoleId { get; set; } public string Name { get; set; }
public abstract class BaseEntity
{
[Key]
public long Id { get; set; }
}
public class User : BaseEntity
{
public long UserRoleId { get; set; }
public string Name { get; set; }
public virtual _EntityUserRole UserRole { get; set; }
}
public class UserRole : BaseEntity
{
public string Name { get; set; }
public virtual ICollection<_EntityUser> Users { get; set; }
public virtual ICollection<_EntityUserPermission> UserPermissions { get; set; }
internal _EntityUserRole()
{
Users = new List<_EntityUser>();
UserPermissions = new List<_EntityUserPermission>();
}
}
public class UserPermission : BaseEntity
{
public string Name { get; set; }
public virtual ICollection<_EntityUserRole> UserRoles { get; set; }
internal _EntityUserPermission()
{
UserRoles = new List<_EntityUserRole>();
}
}
public abstract class BaseEntityMap<T> : EntityTypeConfiguration<T> where T : BaseEntity
{
public BaseEntityMap()
{
ToTable(typeof(T).Name);
HasKey(a => a.Id);
}
}
public class UserMap : BaseEntityMap<User>
{
public UserMap()
: base()
{
HasRequired(x => x.UserRole)
.WithMany(x => x.Users)
.HasForeignKey(x => x.UserRoleId);
}
}
public class UserRoleMap : BaseEntityMap<UserRole>
{
public UserRoleMap()
: base()
{
HasMany(x => x.UserPermissions)
.WithMany(x => x.UserRoles)
.Map(x =>
{
x.MapLeftKey("UserRoleId");
x.MapRightKey("UserPermissionId");
x.ToTable("_EntityUserRole_UserPermission");
});
}
}
public class UserPermissionMap : BaseEntityMap<UserPermission>
{
public UserPermissionMap()
: base()
{
}
}
internal class SqlServerDataContext : DbContext
{
public DbSet<User> Users { get; set; }
public DbSet<UserRole> UserRoles { get; set; }
public DbSet<UserPermission> UserPermissions { get; set; }
public SqlServerDataContext()
: base("Name=MyDB")
{
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Configurations.Add(new UserMap());
modelBuilder.Configurations.Add(new UserRoleMap());
modelBuilder.Configurations.Add(new UserPermissionMap());
base.OnModelCreating(modelBuilder);
}
}
private static void Main()
{
using (SqlServerDataContext ctx = new SqlServerDataContext())
{
UserRole role = new UserRole();
role.Name = "Super";
UserPermission prm1 = new UserPermission();
prm1.Name = "Delete";
role.UserPermissions.Add(prm1);
UserPermission prm2 = new UserPermission();
prm2.Name = "Add";
role.UserPermissions.Add(prm2);
UserPermission prm3 = new UserPermission();
prm3.Name = "Edit";
role.UserPermissions.Add(prm3);
User user = new User();
user.Name = "User 1";
user.UserRole = role;
ctx.Users.Add(user);
ctx.SaveChanges();
}
using (SqlServerDataContext ctx = new SqlServerDataContext())
{
var b = ctx.Users.Find(1);
}
}
结果
与在打印屏幕中一样,在我将一条记录插入到User之后,当我检索回来时,UserPermissions为空。请帮忙!谢谢。将模型添加到集合后,您需要
保存更改()
,以便将模型持久化到数据库中
然后,您可以从数据库中读取所需的内容
在这之后,您需要访问该属性或使用Include(使其更为急切,这是首选用法)
我可以获得UserRole,但无法获得UserPermission。我更新了答案,在我的示例中有一个额外的
Include
@KelvinGoi确实使用System.Data.Entity添加,但我得到了这个错误,error 7'System.Linq.IQueryable'不包含'Find'的定义,并且找不到接受'System.Linq.IQueryable'类型的第一个参数的扩展方法'Find'(您缺少using指令或程序集引用吗?)
@No1\u melman是的,这是因为DbSet
上有这个Find
方法,但是当您开始使用Include
时,您将返回类型更改为IQueryable
。因此,您需要使用FirstOrDefault
查看我的updated@KelvinGo没问题:)
private static void Main()
{
using (SqlServerDataContext ctx = new SqlServerDataContext())
{
UserRole role = new UserRole();
role.Name = "Super";
UserPermission prm1 = new UserPermission();
prm1.Name = "Delete";
role.UserPermissions.Add(prm1);
UserPermission prm2 = new UserPermission();
prm2.Name = "Add";
role.UserPermissions.Add(prm2);
UserPermission prm3 = new UserPermission();
prm3.Name = "Edit";
role.UserPermissions.Add(prm3);
ctx.SaveChanges();
User user = new User();
user.Name = "User 1";
user.UserRole = role;
ctx.Users.Add(user);
ctx.SaveChanges();
}
using (SqlServerDataContext ctx = new SqlServerDataContext())
{
var b = ctx.Users.Find(1);
// Method 1
var roleName = b.UserRole.Name;
// Method 2
ctx.Users.Include(x => x.UserRole).Include(x => x.UserRole.UserPermissions).FirstOrDefault(x => x.Id == 1);
}
}