【EF】EF框架 Code First Fluent API

在Code First方法中，还可以通过Fluent API的方式来处理实体与数据表之间的映射关系。

要使用Fluent API必须在构造自定义的DbContext时，重写OnModelCreating方法，在此方法体内调用Fluent API。

如下面代码所示：

 

  public class BlogDbContext : DbContext
    {
         public BlogDbContext()
            : base("name=BlogDB2005")
        {

        }
         protected override void OnModelCreating(DbModelBuilder modelBuilder)
         {

             //do something
             base.OnModelCreating(modelBuilder);
         }
    }

 

下面来看一些简单的例子

主键

modelBuilder.Entity<BlogUser>().HasKey(user => user.UserId);

联合主键

 //联合主键
 modelBuilder.Entity<BlogUser>().HasKey(user => new { user.UserId, user.BlogName });

字段非空

//要求属性必填
modelBuilder.Entity<BlogUser>().Property(user => user.BlogName).IsRequired();

设定字段最大长度

modelBuilder.Entity<BlogUser>().Property(user => user.BlogName).HasMaxLength(20);

设置复杂属性，相当数据特性中的ComplexType

modelBuilder.ComplexType<Address>();

属性字段不映射到数据表字段，相当于数据特性中的NotMapped

 modelBuilder.Entity<BlogUser>().Ignore(user => user.MyProperty);

设置字段是否自动增长

//设置自动增长，如不需要自动增长，则设为 DatabaseGeneratedOption.None
 modelBuilder.Entity<BlogUser>().Property(user => user.UserId)
              .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);

设置外键

 

 ///产生一对多的关系
  modelBuilder.Entity<Post>()
              .HasRequired(p =>p.BlogUser)
             .WithMany(user => user.Posts)
             .HasForeignKey(p => p.UserId);

  ///与上面等效
  //modelBuilder.Entity<BlogUser>()
          //    .HasMany(user => user.Posts)
          //    .WithRequired(p => p.BlogUser)
          //    .HasForeignKey(p => p.UserId);

 

设定实体映射到数据库中的表名

 modelBuilder.Entity<BlogUser>().ToTable("MyUser");

设置实体属性映射到数据库中的列名

 modelBuilder.Entity<BlogUser>()
             .Property(user => user.Description)
             .HasColumnName("userDescription")
             .HasColumnType("ntext");

下面给出完整代码，方便测试：

  class FluentAPISample
     {

         static void Main(string[] args)
         {
             using (var db = new BlogDbContext())
             {
                 db.Database.Create();
             }
         }
     }

     public class BlogDbContext : DbContext
     {
          public BlogDbContext()
             : base("name=BlogDB2005")
         {
             Database.SetInitializer<BlogDbContext>(
                 new DropCreateDatabaseIfModelChanges<BlogDbContext>()
                 );
         }
          protected override void OnModelCreating(DbModelBuilder modelBuilder)
          {
              modelBuilder.Entity<BlogUser>().HasKey(user => user.UserId);
              //联合主键
              //modelBuilder.Entity<BlogUser>().HasKey(user => new { user.UserId, user.BlogName });

              //设置自动增长，如不需要自动增长，则设为 DatabaseGeneratedOption.None
              modelBuilder.Entity<BlogUser>().Property(user => user.UserId)
                  .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);

              //要求属性必填
              modelBuilder.Entity<BlogUser>().Property(user => user.BlogName).IsRequired();
              modelBuilder.Entity<BlogUser>().Property(user => user.BlogName).HasMaxLength();
              modelBuilder.Entity<BlogUser>().Ignore(user => user.MyProperty);

              modelBuilder.ComplexType<Address>();

              ///产生一对多的关系
              modelBuilder.Entity<Post>()
                  .HasRequired(p =>p.BlogUser)
              .WithMany(user => user.Posts)
              .HasForeignKey(p => p.UserId);

              ///与上面等效
              //modelBuilder.Entity<BlogUser>()
              //    .HasMany(user => user.Posts)
              //    .WithRequired(p => p.BlogUser)
              //    .HasForeignKey(p => p.UserId);

              modelBuilder.Entity<BlogUser>().ToTable("MyUser");

              modelBuilder.Entity<BlogUser>()
                  .Property(user => user.Description)
                  .HasColumnName("userDescription")
                  .HasColumnType("ntext");

              base.OnModelCreating(modelBuilder);
          }
     }

     public partial class BlogUser
     {
         public int UserId { get; set; }
         public string BlogName { get; set; }
         public int MyProperty { get; set; }
         public Address Address { get; set; }
         public string Description { get; set; }
         public virtual ICollection<Post> Posts { get; set; }
     }
     public partial class Post
     {
         public int PostId { get; set; }
         public string PostTitle { get; set; }
         public int UserId { get; set; }
         public BlogUser BlogUser { get; set; }
     }
     public partial class Address
     {
         public string Province { get; set; }
         public string City { get; set; }
     }

  class FluentAPISample
     {

         static void Main(string[] args)
         {
             using (var db = new BlogDbContext())
             {
                 db.Database.Create();
             }
         }
     }

     public class BlogDbContext : DbContext
     {
          public BlogDbContext()
             : base("name=BlogDB2005")
         {
             Database.SetInitializer<BlogDbContext>(
                 new DropCreateDatabaseIfModelChanges<BlogDbContext>()
                 );
         }
          protected override void OnModelCreating(DbModelBuilder modelBuilder)
          {
              modelBuilder.Entity<BlogUser>().HasKey(user => user.UserId);
              //联合主键
              //modelBuilder.Entity<BlogUser>().HasKey(user => new { user.UserId, user.BlogName });

              //设置自动增长，如不需要自动增长，则设为 DatabaseGeneratedOption.None
              modelBuilder.Entity<BlogUser>().Property(user => user.UserId)
                  .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);

              //要求属性必填
              modelBuilder.Entity<BlogUser>().Property(user => user.BlogName).IsRequired();
              modelBuilder.Entity<BlogUser>().Property(user => user.BlogName).HasMaxLength();
              modelBuilder.Entity<BlogUser>().Ignore(user => user.MyProperty);

              modelBuilder.ComplexType<Address>();

              ///产生一对多的关系
              modelBuilder.Entity<Post>()
                  .HasRequired(p =>p.BlogUser)
              .WithMany(user => user.Posts)
              .HasForeignKey(p => p.UserId);

              ///与上面等效
              //modelBuilder.Entity<BlogUser>()
              //    .HasMany(user => user.Posts)
              //    .WithRequired(p => p.BlogUser)
              //    .HasForeignKey(p => p.UserId);

              modelBuilder.Entity<BlogUser>().ToTable("MyUser");

              modelBuilder.Entity<BlogUser>()
                  .Property(user => user.Description)
                  .HasColumnName("userDescription")
                  .HasColumnType("ntext");

              base.OnModelCreating(modelBuilder);
          }
     }

     public partial class BlogUser
     {
         public int UserId { get; set; }
         public string BlogName { get; set; }
         public int MyProperty { get; set; }
         public Address Address { get; set; }
         public string Description { get; set; }
         public virtual ICollection<Post> Posts { get; set; }
     }
     public partial class Post
     {
         public int PostId { get; set; }
         public string PostTitle { get; set; }
         public int UserId { get; set; }
         public BlogUser BlogUser { get; set; }
     }
     public partial class Address
     {
         public string Province { get; set; }
         public string City { get; set; }
     }

运行结果如下图示：