7.9 數據注解特性--ForeignKey - caofangsheng－IT工程師數位筆記本

文章出處

外鍵特性，可以應用到類的屬性中。Code-First默認的約定，對外鍵屬性來說，假定外鍵屬性的名稱和主鍵屬性是匹配的。

我們看一下，下面的代碼：

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EF2
{
    [Table("StudentMaster",Schema="WaHaHa")]
   public class Student
    {
        [Key]
        [Column(Order=5)]
        public int StudentKey1 { get; set; }

        [Key]
        [Column(Order=6)]
        public int StudentKey2 { get; set; }

        
        [MaxLength(20)]
        [ConcurrencyCheck]
        [Required]
        [Column("SName",Order=1,TypeName="nvarchar")]
        public string StudentName { get; set; }

        [NotMapped()]
        public int? Age { get; set; }

      
        public int StdId { get; set; }

        [ForeignKey("StdId")]
        public virtual Standard Standard { get; set; }

      

    }
}

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Text;

namespace EF2
{
   public class Standard
    {
       [Key]
       public int StdId { get; set; }

       public string StandardName { get; set; }
    }
}

從上面的圖中，可以看出，StdId在Student表中是外鍵，在Standard表中是主鍵。

這里是不是用類名+id的做法，使用外鍵。

默認的是使用這樣的：

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EF2
{
    [Table("StudentMaster",Schema="WaHaHa")]
   public class Student
    {
        [Key]
        [Column(Order=5)]
        public int StudentKey1 { get; set; }

        [Key]
        [Column(Order=6)]
        public int StudentKey2 { get; set; }

        
        [MaxLength(20)]
        [ConcurrencyCheck]
        [Required]
        [Column("SName",Order=1,TypeName="nvarchar")]
        public string StudentName { get; set; }

        [NotMapped()]
        public int? Age { get; set; }


        public int StandardId { get; set; }   //類名+ID

        [ForeignKey("StandardId")]
        public virtual Standard Standard { get; set; }

      

    }
}

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Text;

namespace EF2
{
   public class Standard
    {
       [Key]
       public int StandardId { get; set; }     //類名+ID

       public string StandardName { get; set; }
    }
}

看看下面的：

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EF2
{
    [Table("StudentMaster",Schema="WaHaHa")]
   public class Student
    {
        [Key]
        [Column(Order=5)]
        public int StudentKey1 { get; set; }

        [Key]
        [Column(Order=6)]
        public int StudentKey2 { get; set; }

        
        [MaxLength(20)]
        [ConcurrencyCheck]
        [Required]
        [Column("SName",Order=1,TypeName="nvarchar")]
        public string StudentName { get; set; }

        [NotMapped()]
        public int? Age { get; set; }


        public int StandardRefId { get; set; }

        [ForeignKey("StandardRefId")]
        public virtual Standard Standard { get; set; }

      

    }
}

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Text;

namespace EF2
{
   public class Standard
    {
       [Key]
       public int StandardId { get; set; }

       public string StandardName { get; set; }
    }
}