EF5.X Code First表关联与延迟加载
Posted 渐行渐远....那些错过的青春
tags:
篇首语：本文由小常识网(cha138.com)小编为大家整理，主要介绍了EF5.X Code First表关联与延迟加载相关的知识，希望对你有一定的参考价值。
1-指定导航属性，会自动生成外键，命名规则为：“表名_主键名”
2-默认情况下与导航属性的主键名称相同的字段会自动被标记为外键
3-通过[ForeignKey]标记指定实体类的属性为外键，
4-方式2的升级版，与导航属性的主键名称相同的字段会自动被标记为外键，然后指定字段对应的数据库中的列名
案例：
组织架构n : 1【组织用户关联】1 ：n用户
using System;
/**
* 作者：陈杰
* 时间：2012-08-10 00:25
* 功能：公共字段接口
**/
namespace ElegantWM.EntityModel
{
public interface IEntity
{
Guid Id { get; set; }
string CreateUser { get; set; }
DateTime CreateTime { get; set; }
string ModifyUser { get; set; }
DateTime? ModifyTime { get; set; }
Byte[] RowVersion { get; set; }
}
}
using System;
using System.Collections;
using System.ComponentModel;
using System.ComponentModel.DataAnnotations;
/**
* 作者：陈杰
* 时间：2012-08-10 00:25
* 功能：公共字段接口实现类
**/
namespace ElegantWM.EntityModel
{
public class Entity:IEntity
{
public Guid Id { get; set; }
public string CreateUser { get; set; }
public DateTime CreateTime { get; set; }
public string ModifyUser { get; set; }
public DateTime? ModifyTime { get; set; }
1622047412
public Byte[] RowVersion { get; set; }
}
}
以上两个类为数据库实体的公共属性，但随着业务的复杂度增加，感觉提取实体的公共字段并不是很妥当，可适当折中考虑。
/* 组织架构实体 */
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ElegantWM.EntityModel
{
public class WMS_Org : Entity
{
public WMS_Org() { }
public string OrgName { get; set; }
public string OrgDesc { get; set; }
public int OrgOrder { get; set; }
public string OrgFatherId { get; set; }
public virtual ICollection<WMS_OrgUser> OrgUserIds { get; set; }
}
}
/* 用户实体 */
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ElegantWM.EntityModel
{
public class WMS_User : Entity
{
public WMS_User() { }
public string UserName { get; set; }
public string NickName { get; set; }
public string UserPwd { get; set; }
public string Sex { get; set; }
public string Phone { get; set; }
public string Email { get; set; }
public string QQ { get; set; }
public string Address { get; set; }
public string Remark { get; set; }
public virtual ICollection<WMS_OrgUser> UserOrgIds { get; set; }
}
}
/* 用户和组织架构的关系 */
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations.Schema;
using System.Linq;
using System.Text;
namespace ElegantWM.EntityModel
{
public class WMS_OrgUser : Entity
{
public WMS_OrgUser() { }
//3. 指定外键的方式
public Guid OrgId { get; set; }
[ForeignKey("OrgId")]
public virtual WMS_Org Org { get; set; }
public Guid UserId { get; set; }
[ForeignKey("UserId")]
public virtual WMS_User User { get; set; }
//1. 不指定外键，EF默认会生成 对象_表对象ID，也就是Org_Id，User_Id
public virtual WMS_Org Org { get; set; }
public virtual WMS_User User { get; set; }
}
//2. 不适合本案例，因为所有对象的主键都是ID，自动识别
public Guid Id { get; set; }
public virtual WMS_Org Org { get; set; }
......
//4. 指定数据库真实外键名称
[Column("OrgID")]
public Guid Id { get; set; }
public virtual WMS_Org Org { get; set; }
}
根据上面的4个原则，可以在组合出符合自己实际业务的关联类。
建立好了关联类后，需要注意的是，数据库中外键类型必须和主表的主键类型一致，当然外键关系你可以不用强制建立，但类型必须一直，否则会出错。
关联的对象注意声明为virtual，以供延迟加载。
当 EF 访问实体的子实体的时候是如何工作的呢？你的集合是 POCO 的集合，所以，在访问的时候没有事件发生，EF 通过从你定义的实体派生一个动态的对象，然后覆盖你的子实体集合访问属性来实现。这就是为什么需要标记你的子实体集合属性为 virtual 的原因。
执行EF的操作，验证
//1.创建关系
WMS_OrgUser ou = new WMS_OrgUser();
ou.OrgId = Guid.Parse("79DDB55A-1587-4928-A312-58DA0C091459");
ou.UserId = Guid.Parse("9E99FBCF-1517-4ACA-A81D-AE3535AF8E37");
WMFactory.WMSOrgUser.Insert(ou);
//2. 根据关系，已知组织ID，获取用户
WMS_OrgUser orguser = WMFactory.WMSOrgUser.GetById("7E632B62-B8EC-4D58-AE94-A412868146E7");
//正常获取了用户对象，正常打印用户昵称
string name = orguser.User.NickName;
//3.测试贪婪加载，见文章后面
orguser = WMFactory.WMSOrgUser.TestNoLazyLoading(Guid.Parse("7E632B62-B8EC-4D58-AE94-A412868146E7"));
//4.获取组织架构下的用户
WMS_Org org = WMFactory.WMSOrg.GetById("79DDB55A-1587-4928-A312-58DA0C091459");
ICollection<WMS_OrgUser> coll = org.OrgUserIds;
orguser = coll.ToList()[0];
string orguserid=orguser.Id.ToString();
string orgusername = orguser.User.NickName;
关于延迟加载和贪婪加载
1.延迟加载，当对象使用的时候，再去数据库中加载，例如上面的orguser.User，当我调用这句话的时候，EF会到数据库中加载数据
EF默认是开启延迟加载的，禁用如下：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Entity;
using System.Data.Entity.Infrastructure;
using System.Data.Entity.ModelConfiguration.Conventions;
using ElegantWM.EntityModel;
using System.Configuration;
/**
* 作者：陈杰
* ＱＱ：710782046
* 时间：2012-08-10
* 功能：EF配置文件，支持多数据库
**/
namespace ElegantWM.DAL
{
public class DB : DbContext
{
//public static readonly log4net.ILog log = log4net.LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);
//配置连接串,默认数据库DefaultDB
public DB(string _ConnectStr)
: base()
{
Database.Connection.ConnectionString = ConfigurationManager.ConnectionStrings[_ConnectStr].ToString();
Database.SetInitializer<DB>(null);
//这里哦
this.Configuration.LazyLoadingEnabled = false;
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
//已经存在的数据库，不然会出现负数
modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
base.OnModelCreating(modelBuilder);
}
//注册到EF
public DbSet<WMS_Role> wmRole { get; set; }
public DbSet<WMS_User> wmUser { get; set; }
public DbSet<WMS_Org> wmOrg { get; set; }
public DbSet<WMS_Module> wmModule { get; set; }
public DbSet<WMS_RoleModule> wmRoleModule { get; set; }
public DbSet<WMS_UserRole> wmUserRole { get; set; }
public DbSet<WMS_OrgUser> wmsOrgUser { get; set; }
}
}
2.贪懒加载，一次性把数据组织好，加载到内存，类似join表
例如以上案例4，通过组织架构获取用户，EF延迟加载执行的sql如下：
exec sp_executesql N\'SELECT TOP (2) [Extent1].[Id] AS [Id], [Extent1].[OrgName] AS [OrgName], [Extent1].[OrgDesc] AS [OrgDesc], [Extent1].[OrgOrder] AS [OrgOrder], [Extent1].[OrgFatherId] AS [OrgFatherId], [Extent1].[CreateUser] AS [CreateUser], [Extent1].[CreateTime] AS [CreateTime], [Extent1].[ModifyUser] AS [ModifyUser], [Extent1].[ModifyTime] AS [ModifyTime], [Extent1].[RowVersion] AS [RowVersion] FROM [dbo].[WMS_Org] AS [Extent1] WHERE [Extent1].[Id] = @p__linq__0\',N\'@p__linq__0 uniqueidentifier\',@p__linq__0=\'79DDB55A-1587-4928-A312-58DA0C091459\' exec sp_executesql N\'SELECT [Extent1].[Id] AS [Id], [Extent1].[OrgId] AS [OrgId], [Extent1].[UserId] AS [UserId], [Extent1].[CreateUser] AS [CreateUser], [Extent1].[CreateTime] AS [CreateTime], [Extent1].[ModifyUser] AS [ModifyUser], [Extent1].[ModifyTime] AS [ModifyTime], [Extent1].[RowVersion] AS [RowVersion] FROM [dbo].[WMS_OrgUser] AS [Extent1] WHERE [Extent1].[OrgId] = @EntityKeyValue1\',N\'@EntityKeyValue1 uniqueidentifier\',@EntityKeyValue1=\'79DDB55A-1587-4928-A312-58DA0C091459\' exec sp_executesql N\'SELECT [Extent1].[Id] AS [Id], [Extent1].[UserName] AS [UserName], [Extent1].[NickName] AS [NickName], [Extent1].[UserPwd] AS [UserPwd], [Extent1].[Sex] AS [Sex], [Extent1].[Phone] AS [Phone], [Extent1].[Email] AS [Email], [Extent1].[QQ] AS [QQ], [Extent1].[Address] AS [Address], [Extent1].[Remark] AS [Remark], [Extent1].[CreateUser] AS [CreateUser], [Extent1].[CreateTime] AS [CreateTime], [Extent1].[ModifyUser] AS [ModifyUser], [Extent1].[ModifyTime] AS [ModifyTime], [Extent1].[RowVersion] AS [RowVersion] FROM [dbo].[WMS_User] AS [Extent1] WHERE [Extent1].[Id] = @EntityKeyValue1\',N\'@EntityKeyValue1 uniqueidentifier\',@EntityKeyValue1=\'9D001F8D-E304-4DB3-B5C0-7C5139E888A6\'
贪婪加载的方式，如测试3，产生的SQL如下：
public WMS_OrgUser TestNoLazyLoading(Guid id)
{
return DBSET.Include("User").Include("Org").FirstOrDefault(o => o.Id == id);
}
exec sp_executesql N\'SELECT
1 AS [C1],
[Limit1].[Id] AS [Id],
[Limit1].[OrgId] AS [OrgId],
[Limit1].[UserId] AS [UserId],
[Limit1].[CreateUser] AS [CreateUser],
[Limit1].[CreateTime] AS [CreateTime],
[Limit1].[ModifyUser] AS [ModifyUser],
[Limit1].[ModifyTime] AS [ModifyTime],
[Limit1].[RowVersion] AS [RowVersion],
[Extent2].[Id] AS [Id1],
[Extent2].[UserName] AS [UserName],
[Extent2].[NickName] AS [NickName],
[Extent2].[UserPwd] AS [UserPwd],
[Extent2].[Sex] AS [Sex],
[Extent2].[Phone] AS [Phone],
[Extent2].[Email] AS [Email],
[Extent2].[QQ] AS [QQ],
[Extent2].[Address] AS [Address],
[Extent2].[Remark] AS [Remark],
[Extent2].[CreateUser] AS [CreateUser1],
[Extent2].[CreateTime] AS [CreateTime1],
[Extent2].[ModifyUser] AS [ModifyUser1],
[Extent2].[ModifyTime] AS [ModifyTime1],
[Extent2].[RowVersion] AS [RowVersion1],
[Extent3].[Id] AS [Id2],
[Extent3].[OrgName] AS [OrgName],
[Extent3].[OrgDesc] AS [OrgDesc],
[Extent3].[OrgOrder] AS [OrgOrder],
[Extent3].[OrgFatherId] AS [OrgFatherId],
[Extent3].[CreateUser] AS [CreateUser2],
[Extent3].[CreateTime] AS [CreateTime2],
[Extent3].[ModifyUser] AS [ModifyUser2],
[Extent3].[ModifyTime] AS [ModifyTime2],
[Extent3].[RowVersion] AS [RowVersion2]
FROM (SELECT TOP (1) [Extent1].[Id] AS [Id], [Extent1].[OrgId] AS [OrgId], [Extent1].[UserId] AS [UserId], [Extent1].[CreateUser] AS [CreateUser], [Extent1].[CreateTime] AS [CreateTime], [Extent1].[ModifyUser] AS [ModifyUser], [Extent1].[ModifyTime] AS [ModifyTime], [Extent1].[RowVersion] AS [RowVersion]
FROM [dbo].[WMS_OrgUser] AS [Extent1]
WHERE [Extent1].[Id] = @p__linq__0 ) AS [Limit1]
LEFT OUTER JOIN [dbo].[WMS_User] AS [Extent2] ON [Limit1].[UserId] = [Extent2].[Id]
LEFT OUTER JOIN [dbo].[WMS_Org] AS [Extent3] ON [Limit1].[OrgId] = [Extent3].[Id]\',N\'@p__linq__0 uniqueidentifier\',@p__linq__0=\'7E632B62-B8EC-4D58-AE94-A412868146E7\'
以上是关于EF5.X Code First表关联与延迟加载的主要内容，如果未能解决你的问题，请参考以下文章
mybatis基础系列——关联查询延迟加载一级缓存与二级缓存
一文搞定Mybatis 一对多延迟加载，并且子查询中与主表字段不对应