Data Annotation Feature -- ForeignKey, annotation -- foreignkey

Data Annotation Feature -- ForeignKey, annotation -- foreignkey

The foreign key feature can be applied to class attributes. The default Code-First Convention assumes that the name of the foreign key attribute matches the primary key attribute.

Let's take a look at the following code:

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; }    }}

As shown in the preceding figure, StdId is a foreign key in Student table and a primary key in Standard table.

Whether to use the class name + id or not.

By default, this is used:

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; s Et;} [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;} // class name + ID [ForeignKey ("StandardId")] public virtual 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;} // class name + ID public string StandardName {get; set ;}}}

 

Take a look at the following:

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; }    }}

View database:

 

This means that we can randomly specify the foreign key name, haha, haha...