EF5.X Code First表关联与延迟加载

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EF5.X Code First表关联与延迟加载

2024-08-10 22:51:28 217人阅读

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; }        [Timestamp]        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‘

EF5.X Code First表关联与延迟加载

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