這里使用相冊Album和圖片Picture的關系做示例

1，Album與Picture最基本的關系是1-n(一個相冊可以有多張圖片)

? ?這時Album、Picture實體類可以這么定義

/// <summary>/// 相冊/// </summary>public class Album{public int ID { get; set; }/// <summary>/// 標題/// </summary>public string Title { get; set; }public DateTime CreateTime { get; set; }/// <summary>/// 擁有者/// </summary>public virtual User Owner { get; set; } }

　　

/// <summary>/// 圖片/// </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>/// 所屬相冊/// </summary>public virtual Album Album { get; set; }}

生成的表結構

2，后來就要改需求了，相冊要加一個封面

于是Album與Picture的關系就加了一個1-1（一個相冊只有一個封面）

這樣就需要配置一下實體關系來區分屬性之間的關系

Album和Picture類做一些修改

?

/// <summary>/// 相冊/// </summary>public class Album{public int ID { get; set; }/// <summary>/// 標題/// </summary>public string Title { get; set; }public DateTime CreateTime { get; set; }/// <summary>/// 擁有者/// </summary>public virtual User Owner { get; set; }/// <summary>/// 封面/// </summary>public virtual Picture Cover { get; set; }/// <summary>/// 相冊下的圖片列表/// </summary>public virtual ICollection<Picture> Pictures { get; set; }}

?

　　

/// <summary>/// 圖片/// </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>/// 所屬相冊/// </summary>public virtual Album Album { get; set; }}

然后添加一個映射類

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

EF上下文類中重寫方法

protected override void OnModelCreating(DbModelBuilder modelBuilder){modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();//移除復數表名的契約modelBuilder.Configurations.Add(new AlbumMap());}

數據庫遷移時生成的代碼：

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");}}

最終表結構

?上一節：【EF Code First】 一對多、多對多的多重關系配置

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轉載于:https://www.cnblogs.com/Sunlimi/p/4348299.html

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