在上一篇中，讲述了用数据特性的方式来标识实体与数据表之间的映射关系，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：
publicclass BlogDbContext : DbContext { public BlogDbContext() : base("name=BlogDB2005") { } protectedoverridevoid 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");
完整代码
class FluentAPISample
{staticvoid Main(string[] args)
{ using (var db =new BlogDbContext()) { db.Database.Create(); } } }publicclass BlogDbContext : DbContext
{ public BlogDbContext() : base("name=BlogDB2005") { Database.SetInitializer<BlogDbContext>( new DropCreateDatabaseIfModelChanges<BlogDbContext>() ); } protectedoverridevoid 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(20); 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);
} }publicpartialclass BlogUser
{ publicint UserId { get; set; } publicstring BlogName { get; set; } publicint MyProperty { get; set; } public Address Address { get; set; } publicstring Description { get; set; } publicvirtual ICollection<Post> Posts { get; set; } } publicpartialclass Post { publicint PostId { get; set; } publicstring PostTitle { get; set; } publicint UserId { get; set; } public BlogUser BlogUser { get; set; } } publicpartialclass Address { publicstring Province { get; set; } publicstring City { get; set; } }