public class BaseModel
{
public int Id { get; set; }
public DateTime CreateDateTime { get; set; }
}
public class Address
{
public string Street { get; set; }
public string City { get; set; }
public string ZipCode { get; set; }
}
public class User:BaseModel
{
public string Name {get;set;}
public string Birthdate {get;set;}
public string IdNumber {get;set;}
public Address Address {get;set;}
}
以上代码在ORM中称为组合类,EF会将这两个类映射在一张表中。当Code First发现不能推断出类的主键,并且没有通过Data Annotations或Fluent API注册主键,那么该类型将被自动注册为复杂类型。
注意:
我们接下来创建 DbContext 类
public class EfDbContext : DbContext
{
public EfDbContext()
{
Database.SetInitializer(new DropCreateDatabaseIfModelChanges<EfDbContext>());
}
public DbSet<User> Users { get; set; }
}
创建完DbContext类后,我们编写将数据存入数据库的方法:
using (var efDbContext = new EfDbContext())
{
var user = new User()
{
Birthdate = DateTime.Now,
CreateDateTime = DateTime.Now,
Name = "张三",
IdNumber = "1234567"
};
efDbContext.Users.Add(user);
efDbContext.SaveChanges();
}
运行上述代码,会得到如下错误:
出现上述错误的原因是我们没有初始化 Address 类,其中一个(后面我会讲解另一个解决方法)解决方法是在 new User(){} 内初始化 Address,修正后的代码如下:
using (var efDbContext = new EfDbContext())
{
var user = new User()
{
Birthdate = DateTime.Now,
CreateDateTime = DateTime.Now,
Name = "张三",
IdNumber = "1234567",
Address = new Address()
};
efDbContext.Users.Add(user);
efDbContext.SaveChanges();
}
现在我们按照上面所述,对我们先前编写的内容进行改造,这三条规则也是解决我们前面所遇到的BUG的另一个方法。
public class BaseModel
{
public int Id { get; set; }
public DateTime CreateDateTime { get; set; }
}
public class Address
{
public string Street { get; set; }
public string City { get; set; }
public string ZipCode { get; set; }
public bool HasValue
{
get
{
return (Street != null || ZipCode != null || City != null);
}
}
}
public class User : BaseModel
{
public User()
{
Address = new Address();
}
public string Name { get; set; }
public DateTime Birthdate { get; set; }
public string IdNumber { get; set; }
public Address Address { get; set; }
}
public class EfDbContext : DbContext
{
public EfDbContext()
{
Database.SetInitializer(new DropCreateDatabaseIfModelChanges<EfDbContext>());
}
public virtual void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.ComplexType<Address>();
}
public DbSet<User> Users { get; set; }
}
代码改造后我们可以轻松的通过 变更追踪API 来访问数据的原始值和当前值。所谓原始值就是从数据库查询出来的值,当前值就是实体目前的值。入口点是 DbContext的Entry方法,返回对象类型是 DbEntityEntry 。我们看一下访问原始值和当前值得例子:
using (var efDbContext = new EfDbContext())
{
var user = efDbContext.Users.Find(1);
var oriValue = efDbContext.Entry(user).ComplexProperty(u => u.Address).OriginalValue;
//将city的值改为北京
user.Address.City = "北京";
var curValue = efDbContext.Entry(user).ComplexProperty(u => u.Address).CurrentValue;
Console.WriteLine("原始值:"+oriValue.City+" 当前值:"+curValue.City);
Console.Read();
}
运行上述代码,将会看到如下的输出:
同样,我们也可以通过链式调用,获取复杂了类型的属性或者设置复杂类型的属性:
var user = efDbContext.Users.Find(1);
var city = efDbContext.Entry(user).ComplexProperty(u => u.Address).Property(a => a.City).CurrentValue;
Console.Write(city);
从上面的讲解我们卡一看到,用复杂类型很双,一直用一直爽,但是复杂类型还是有他的限制的: