一：Savechange的时候，怎么知道哪些entity被add，modify，delete，unchange ？？？？

如何来辨别。。。

在entity中打上标记来做表示。。。已经被跟踪了。。。当每个entity被打上标记之后，我们才可以

从这些标记获取相应的操作。。。

二：ef如何做到的。。 ObjectStateManager类来管理每个entity的标记。。。

private Dictionary<EntityKey, EntityEntry> _addedEntityStore;

private Dictionary<EntityKey, EntityEntry> _deletedEntityStore;

private Dictionary<EntityKey, EntityEntry> _modifiedEntityStore;

private Dictionary<EntityKey, EntityEntry> _unchangedEntityStore;

private void AddEntityEntryToDictionary

DbSet.Add 做的操作 将新的entity塞入到指定的dic中。。。

SaveChange获取的时候：

this.PullModifiedEntriesFromStateManager();

this.PullUnchangedEntriesFromStateManager();

private void PullModifiedEntriesFromStateManager()
{
foreach (System.Data.Entity.Core.IEntityStateEntry entry in this._stateManager.GetEntityStateEntries(EntityState.Added))
{
if (!entry.IsRelationship && !entry.IsKeyEntry)
{
this.KeyManager.RegisterKeyValueForAddedEntity(entry);
}
}
foreach (System.Data.Entity.Core.IEntityStateEntry entry2 in this._stateManager.GetEntityStateEntries(EntityState.Modified | EntityState.Deleted | EntityState.Added))
{
this.RegisterReferentialConstraints(entry2);
}
foreach (System.Data.Entity.Core.IEntityStateEntry entry3 in this._stateManager.GetEntityStateEntries(EntityState.Modified | EntityState.Deleted | EntityState.Added))
{
this.LoadStateEntry(entry3);
}
}

internal virtual IEnumerable<ObjectStateEntry> GetObjectStateEntriesInternal(EntityState state)
{
ObjectStateEntry[] entryArray = new ObjectStateEntry[this.GetObjectStateEntriesCount(state)];
int num = 0;
if (((EntityState.Added & state) != 0) && (this._addedRelationshipStore != null))
{
foreach (KeyValuePair<RelationshipWrapper, RelationshipEntry> pair in this._addedRelationshipStore)
{
entryArray[num++] = pair.Value;
}
}
if (((EntityState.Deleted & state) != 0) && (this._deletedRelationshipStore != null))
{
foreach (KeyValuePair<RelationshipWrapper, RelationshipEntry> pair2 in this._deletedRelationshipStore)
{
entryArray[num++] = pair2.Value;
}
}
if (((EntityState.Unchanged & state) != 0) && (this._unchangedRelationshipStore != null))
{
foreach (KeyValuePair<RelationshipWrapper, RelationshipEntry> pair3 in this._unchangedRelationshipStore)
{
entryArray[num++] = pair3.Value;
}
}
if (((EntityState.Added & state) != 0) && (this._addedEntityStore != null))
{
foreach (KeyValuePair<EntityKey, EntityEntry> pair4 in this._addedEntityStore)
{
entryArray[num++] = pair4.Value;
}
}
if (((EntityState.Modified & state) != 0) && (this._modifiedEntityStore != null))
{
foreach (KeyValuePair<EntityKey, EntityEntry> pair5 in this._modifiedEntityStore)
{
entryArray[num++] = pair5.Value;
}
}
if (((EntityState.Deleted & state) != 0) && (this._deletedEntityStore != null))
{
foreach (KeyValuePair<EntityKey, EntityEntry> pair6 in this._deletedEntityStore)
{
entryArray[num++] = pair6.Value;
}
}
if (((EntityState.Unchanged & state) != 0) && (this._unchangedEntityStore != null))
{
foreach (KeyValuePair<EntityKey, EntityEntry> pair7 in this._unchangedEntityStore)
{
entryArray[num++] = pair7.Value;
}
}
return entryArray;
}

GetEntityStateEntries

var state=db.Entity(obj).State;

db.Entity(obj).State=EntityState.Add

三：既然我们savechange是的时候，是通过entity的状态去获取。。。

//
// 摘要:
// Describes the state of an entity.
[Flags]
[SuppressMessage("Microsoft.Naming", "CA1714:FlagsEnumsShouldHavePluralNames")]
public enum EntityState
{
//
// 摘要:
// The entity is not being tracked by the context. An entity is in this state immediately
// after it has been created with the new operator or with one of the System.Data.Entity.DbSet
// Create methods.
Detached = 1,
//
// 摘要:
// The entity is being tracked by the context and exists in the database, and its
// property values have not changed from the values in the database.
Unchanged = 2,
//
// 摘要:
// The entity is being tracked by the context but does not yet exist in the database.
Added = 4,
//
// 摘要:
// The entity is being tracked by the context and exists in the database, but has
// been marked for deletion from the database the next time SaveChanges is called.
Deleted = 8,
//
// 摘要:
// The entity is being tracked by the context and exists in the database, and some
// or all of its property values have been modified.
Modified = 16
}

using (SchoolDBEntities db = new SchoolDBEntities())
{
var item = db.Students.FirstOrDefault();

item.StudentName = "asdfasdfasdfasd";

db.SaveChanges();
}

//有一个比较器，来判断是”局部修改“ 还是 ”全局修改“。。。。

仓储模式的必然之路，如何跟踪entity的变化。。。。