EF框架step by step(9)—Code First Fluent API

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：

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：

完整代码

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( 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);
}
}

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：