在我的DbContext子类中,我重写了SaveChanges()方法,因此我可以实现一种类似触发器的功能(在实际保存更改之前).
现在,在某些触发器中,有必要检测某些关系是否已经改变,无论多对多,一对一/零等.
现在,在某些触发器中,有必要检测某些关系是否已经改变,无论多对多,一对一/零等.
我已经阅读了互联网上的一些帖子,包括本网站上的一些帖子,提到DbContext API没有公开任何获取关系信息的方法.
但是,ObjectContext应该能够.
我的SaveChanges方法:
- public override int SaveChanges()
- {
- IEntity entity;
- ChangeTracker.DetectChanges();
- var stateManager = ((IObjectContextAdapter)this).ObjectContext.ObjectStateManager;
- var added = stateManager.GetObjectStateEntries(EntityState.Added).ToList();
- var updated = stateManager.GetObjectStateEntries(EntityState.Modified).ToList();
- var deleted = stateManager.GetObjectStateEntries(EntityState.Deleted).ToList();
- var unchanged = stateManager.GetObjectStateEntries(EntityState.Unchanged).ToList();
- while ((entity = _entitiesRequiringTriggering.FirstOrDefault(x => x.Value).Key) != null)
- {
- _entitiesRequiringTriggering[entity] = false;
- var entry = ChangeTracker.Entries<IEntity>().SingleOrDefault(x => x.State != EntityState.Unchanged && x.Entity == entity);
- if (entry == null) continue;
- var trigger = Triggers.Triggers.GetTriggerForEntity(entry.Entity,this);
- if (trigger == null) continue;
- trigger.BeforeSave(entry.Entity);
- switch (entry.State)
- {
- case EntityState.Added:
- trigger.BeforeAdd(entry.Entity);
- break;
- case EntityState.Modified:
- trigger.BeforeUpdate(entry.Entity);
- break;
- case EntityState.Deleted:
- trigger.BeforeDelete(entry.Entity);
- break;
- }
- }
- return base.SaveChanges();
- }
请注意添加,更新,删除和更改的四个变量.
根据我到目前为止所发现的,GetObjectStateEntries应该返回ObjectStateEntry的集合,该集合具有IsRelationship属性.
我在测试应用程序中运行以下代码:
- using (var db = container.Resolve<IDatabaseContext>())
- {
- var cus = db.Query<Customer>().Single(x => x.Id == 1);
- var newAddress = db.Query<Address>().Single(x => x.Id == 5);
- cus.Address = newAddress; //also sets the foreign key property Customer.AddressId to its new corresponding value
- db.SaveChanges();
- }
当我在调用后检查SaveChanges中的代码时,我得到了预期的结果:
一个结果在更新列表中,Customer对象.
但在任何时候,我都没有获得关系(一对一)Customer_Address的ObjectStateEntry.
我需要能够在关系发生变化时如前所述进行检测.
对于正常的标量属性,您可以这样做:
- var changed = DbEntry.Property(x => x.Name).OriginalValue == DbEntry.Property(x => x.Name).CurrentValue;
但对于不明显起作用的参考属性.
有任何想法吗?
解决方法
您可以使用此ExtensionMethod获取已更改的关系列表
- public static class DbContextExtensions
- {
- public static IEnumerable<Tuple<object,object>> GetRelationships(
- this DbContext context)
- {
- return GetAddedRelationships(context)
- .Union(GetDeletedRelationships(context));
- }
- public static IEnumerable<Tuple<object,object>> GetAddedRelationships(
- this DbContext context)
- {
- return GetRelationships(context,EntityState.Added,(e,i) => e.CurrentValues[i]);
- }
- public static IEnumerable<Tuple<object,object>> GetDeletedRelationships(
- this DbContext context)
- {
- return GetRelationships(context,EntityState.Deleted,i) => e.OriginalValues[i]);
- }
- private static IEnumerable<Tuple<object,object>> GetRelationships(
- this DbContext context,EntityState relationshipState,Func<ObjectStateEntry,int,object> getValue)
- {
- context.ChangeTracker.DetectChanges();
- var objectContext = ((IObjectContextAdapter)context).ObjectContext;
- return objectContext.ObjectStateManager
- .GetObjectStateEntries(relationshipState)
- .Where(e => e.IsRelationship)
- .Select(
- e => Tuple.Create(
- objectContext.GetObjectByKey((EntityKey)getValue(e,0)),objectContext.GetObjectByKey((EntityKey)getValue(e,1))));
- }
- }