MVC Code First中的惯例（约定）

主健

如果Model中包含如下字段（不区分大小写，按优先级列出），则会当做主健

1. 'Id'

2. [type name]Id

　　参考：http://msdn.microsoft.com/en-us/library/system.data.entity.modelconfiguration.conventions.idkeydiscoveryconvention(v=vs.103).aspx

 

外健

采用如下方法定义外健

public class Department
{
    // Primary key
    public int DepartmentID { get; set; }
    public string Name { get; set; }
 
    // Navigation property
    public virtual ICollection<Course> Courses { get; set; }
}
 
public class Course
{
    // Primary key
    public int CourseID { get; set; }
 
    public string Title { get; set; }
    public int Credits { get; set; }
 
    // Foreign key
    public int DepartmentID { get; set; }
 
    // Navigation properties
    public virtual Department Department { get; set; }
}

当一个Model有两个外健时，如

public class Comment
    {
        public int CommentId { get; set; }

        #region Foreign key & Navigation property
        // Foreign key
        public int VideoId { get; set; }
        // Navigation property
        public virtual Video Video { get; set; }

        // Foreign key
        public int AccountId { get; set; }
        // Navigation property
        public virtual Account Account { get; set; }
        #endregion
    }

程序会报类似如下错误：

Introducing FOREIGN KEY constraint 'SalesOrder_Invoices' on table 'Invoices' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.

原因分析：

针对一对多关系，EF自动设置级联删除。

解决办法：

    public class StarObjectContext : DbContext
    {
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
　　　　　　　modelBuilder.Conventions.Remove<OneToManyCascadeDeleteConvention>();   //取消级联删除设置
            base.OnModelCreating(modelBuilder);
        }
    }

也可以单独取消某个Model的设置

modelBuilder.Entity<...>()
            .HasRequired(...)
            .WithMany(...)
            .HasForeignKey(...)
            .WillCascadeOnDelete(false);

参考资料：

http://stackoverflow.com/questions/5532810/entity-framework-code-first-defining-relationships-keys

http://msdn.microsoft.com/en-us/data/jj679962