【EF Code First】 一对一、一对多的多重关系配置

这里使用相册Album和图片Picture的关系做示例

1，Album与Picture最基本的关系是1-n(一个相册可以有多张图片)

   这时Album、Picture实体类可以这么定义

   /// <summary>
    /// 相册
    /// </summary>
    public class Album
    {
        public int ID { get; set; }
        /// <summary>
        /// 标题
        /// </summary>
        public string Title { get; set; }
        public DateTime CreateTime { get; set; }
        /// <summary>
        /// 拥有者
        /// </summary>
        public virtual User Owner { get; set; }       
    }

　　

/// <summary>
    /// 图片
    /// </summary>
    public class Picture
    {
        public long ID { get; set; }

        public string Title { get; set; }

        public string Uri { get; set; }

        public DateTime CreateTime { get; set; }

        /// <summary>
        /// 所属相册
        /// </summary>
        public virtual Album Album { get; set; }
    }

生成的表结构

2，后来就要改需求了，相册要加一个封面

于是Album与Picture的关系就加了一个1-1（一个相册只有一个封面）

这样就需要配置一下实体关系来区分属性之间的关系

Album和Picture类做一些修改

/// <summary>
    /// 相册
    /// </summary>
    public class Album
    {
        public int ID { get; set; }
        /// <summary>
        /// 标题
        /// </summary>
        public string Title { get; set; }
        public DateTime CreateTime { get; set; }
        /// <summary>
        /// 拥有者
        /// </summary>
        public virtual User Owner { get; set; }
        /// <summary>
        /// 封面
        /// </summary>
        public virtual Picture Cover { get; set; }
        /// <summary>
        /// 相册下的图片列表
        /// </summary>
        public virtual ICollection<Picture> Pictures { get; set; }
    }

　　

 /// <summary>
    /// 图片
    /// </summary>
    public class Picture
    {
        public long ID { get; set; }

        public string Title { get; set; }

        public string Uri { get; set; }

        public DateTime CreateTime { get; set; }

        /// <summary>
        /// 所属相册
        /// </summary>
        public virtual Album Album { get; set; }
    }

然后添加一个映射类

 public class AlbumMap:EntityTypeConfiguration<Album>
    {
        public AlbumMap() {
            this.HasMany<Picture>(a => a.Pictures).WithRequired(p=>p.Album);
        }
    }

EF上下文类中重写方法

 protected override void OnModelCreating(DbModelBuilder modelBuilder)
       {
           modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();//移除复数表名的契约
           modelBuilder.Configurations.Add(new AlbumMap());
       }

数据库迁移时生成的代码：

 public partial class AlbumAddCover : DbMigration
    {
        public override void Up()
        {
            DropForeignKey("dbo.Picture", "Album_ID", "dbo.Album");
            DropIndex("dbo.Picture", new[] { "Album_ID" });
            AddColumn("dbo.Album", "Cover_ID", c => c.Long());
            AlterColumn("dbo.Picture", "Album_ID", c => c.Int(nullable: false));
            CreateIndex("dbo.Album", "Cover_ID");
            CreateIndex("dbo.Picture", "Album_ID");
            AddForeignKey("dbo.Album", "Cover_ID", "dbo.Picture", "ID");
            AddForeignKey("dbo.Picture", "Album_ID", "dbo.Album", "ID", cascadeDelete: true);
        }
        
        public override void Down()
        {
            DropForeignKey("dbo.Picture", "Album_ID", "dbo.Album");
            DropForeignKey("dbo.Album", "Cover_ID", "dbo.Picture");
            DropIndex("dbo.Picture", new[] { "Album_ID" });
            DropIndex("dbo.Album", new[] { "Cover_ID" });
            AlterColumn("dbo.Picture", "Album_ID", c => c.Int());
            DropColumn("dbo.Album", "Cover_ID");
            CreateIndex("dbo.Picture", "Album_ID");
            AddForeignKey("dbo.Picture", "Album_ID", "dbo.Album", "ID");
        }
    }

最终表结构

 上一节：【EF Code First】 一对多、多对多的多重关系配置

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------