问题是更新由实体关系组成的聚合.
例如,采取Order和OrderItem关系.聚合根是管理自己的OrderItem集合的Order.因此,OrderRepository将负责更新整个聚合(不会有OrderItemRepository).
数据持久性使用实体框架6进行处理.
更新存储库方法(DbContext.SaveChanges()发生在别处)：
public void Update(TDataEntity item)
{
var entry = context.Entry<TDataEntity>(item);
if (entry.State == EntityState.Detached)
{
var set = context.Set<TDataEntity>();
TDataEntity attachedEntity = set.Local.SingleOrDefault(e => e.Id.Equals(item.Id));
if (attachedEntity != null)
{
// If the identity is already attached,rather set the state values
var attachedEntry = context.Entry(attachedEntity);
attachedEntry.CurrentValues.SetValues(item);
}
else
{
entry.State = EntityState.Modified;
}
}
}
在我上面的例子中,只有Order实体才会被更新,而不是相关的OrderItem集合.
我必须附加所有的OrderItem实体吗？我怎么能这样做呢？
她写道：
When a disconnected entity graph arrives on the server side,the
server will not know the state of the entities. You need to provide a
way for the state to be discovered so that the context can be made
aware of each entity’s state.
这种技术叫做画状态.
主要有两种方法：
>通过图形迭代,使用您对模型的知识,并为每个实体设置状态
建立跟踪状态的通用方法
第二个选项是非常好的,它包括创建一个界面,您的模型中的每个实体都将实现. Julie使用一个IObjectWithState接口来告诉实体的当前状态：
public interface IObjectWithState
{
State State { get; set; }
}
public enum State
{
Added,Unchanged,Modified,Deleted
}
首先要做的是通过挂起在Context类中添加构造函数的事件自动设置为从DB检索的每个实体不变：
public YourContext()
{
((IObjectContextAdapter)this).ObjectContext
.ObjectMaterialized += (sender,args) =>
{
var entity = args.Entity as IObjectWithState;
if (entity != null)
{
entity.State = State.Unchanged;
}
};
}
然后更改您的Order和OrderItem类以实现IObjectWithState接口,并调用接受根实体的ApplyChanges方法作为参数：
private static void ApplyChanges<TEntity>(TEntity root)
where TEntity : class,IObjectWithState
{
using (var context = new YourContext())
{
context.Set<TEntity>().Add(root);
CheckForEntitiesWithoutStateInterface(context);
foreach (var entry in context.ChangeTracker
.Entries<IObjectWithState>())
{
IObjectWithState stateInfo = entry.Entity;
entry.State = ConvertState(stateInfo.State);
}
context.SaveChanges();
}
}
private static void CheckForEntitiesWithoutStateInterface(YourContext context)
{
var entitiesWithoutState =
from e in context.ChangeTracker.Entries()
where !(e.Entity is IObjectWithState)
select e;
if (entitiesWithoutState.Any())
{
throw new NotSupportedException("All entities must implement IObjectWithState");
}
}
最后但并非最不重要的是,不要忘了在调用ApplyChanges之前设置图形的正确状态;-)(甚至可以在同一个图形中混合修改和删除的状态)
朱莉建议在他的书中更进一步：
you may find yourself wanting to be more granular with the way
modified properties are tracked. Rather than marking the entire entity
as modified,you might want only the properties that have actually
changed to be marked as modified.
In addition to marking an entity as modified,the client is also
responsible for recording which properties have been modified. One way
to do this would be to add a list of modified property names to the
state tracking interface.
但是,由于我的答案已经太久了,如果你想了解更多,请去看她的book
