Entity Framework Code First 一對多關聯設定

Nov 25, 2014

2 mins read

兩個類別之間，一個包含集合導覽屬性，一個包含引用屬性，就會被當成一對多關系

主表

namespace ConsoleApplication1.Models
{
    using System.Collections.Generic;
    using System.ComponentModel.DataAnnotations.Schema;
[Table("Topic")]
public class Topic
{
    public int TopicId { get; set; }

    public string Title { get; set; }

    public virtual ICollection&lt;Reply&gt; Reply { get; set; }
}

}

明細表外鍵的命名只有符合預設的規則，就會建立關系，規則如下 1. 目標類型索引的名稱 2. 目標類型名稱+目標類型主索引名稱 3. 導覽屬性名稱+目標類型主索引名稱

namespace ConsoleApplication1.Models
{
    using System.ComponentModel.DataAnnotations.Schema;
[Table("Reply")]
public class Reply
{
    public int ReplyId { get; set; }

    public int TopicId { get; set; }
    // public int TopicTopicId { get; set; }
    // public int TheTopicTopicId { get; set; }

    public string Title { get; set; }

    public virtual Topic TheTopic { get; set; }
}

}

若不是用預設規則的命名方式，可以透過ForeignKey這個Attribute設定

namespace ConsoleApplication1.Models
{
    using System.ComponentModel.DataAnnotations.Schema;
[Table("Reply")]
public class Reply
{
    public int ReplyId { get; set; }

    [ForeignKey("TheTopic")]
    public int tid { get; set; }

    public string Title { get; set; }

    public virtual Topic TheTopic { get; set; }
}

}

也可以設定在引用屬性上

namespace ConsoleApplication1.Models
{
    using System.ComponentModel.DataAnnotations.Schema;
[Table("Reply")]
public class Reply
{
    public int ReplyId { get; set; }

    public int tid { get; set; }

    public string Title { get; set; }

    [ForeignKey("tid")]
    public virtual Topic TheTopic { get; set; }
}

}

透過FluentAPI設定方式

namespace ConsoleApplication1.Models
{
    using System.Data.Entity;
public class DemoContext : DbContext
{
    public DbSet&lt;Topic&gt; Topic { get; set; }

    public DbSet&lt;Reply&gt; Reply { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity&lt;Topic&gt;()
            .HasMany(x =&gt; x.Reply)
            .WithRequired(x =&gt; x.TheTopic)
            .HasForeignKey(x =&gt; x.tid)
            .WillCascadeOnDelete(true);
    }
}

}

資料表建立的樣子

[![](http://4.bp.blogspot.com/-x8Be3G5KSmE/VHQ8NnYctyI/AAAAAAAABwk/2MeEYOuWK8c/s1600/01.png)](http://4.bp.blogspot.com/-x8Be3G5KSmE/VHQ8NnYctyI/AAAAAAAABwk/2MeEYOuWK8c/s1600/01.png)

關聯圖

[![](http://3.bp.blogspot.com/-h0YFZrs6BNg/VHQ8RG_hqqI/AAAAAAAABws/K-w1Qjy3owY/s1600/02.png)](http://3.bp.blogspot.com/-h0YFZrs6BNg/VHQ8RG_hqqI/AAAAAAAABws/K-w1Qjy3owY/s1600/02.png)