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; }
}
