本文通过两个测试案例详细探讨了DevExpress XPO框架中Session管理和缓存机制的具体表现，包括对象在不同Session间的行为、刷新机制的限制及缓存管理策略，为开发者提供实践指导。
之前整理了一下XPO在Session管理和缓存方面的一些资料(XPO:Session管理与缓存--机制篇)，但原文的例程还是有些含糊的地方，这两天抽空做了一下测试。若有不当或者不对的地方敬请不吝赐教。
XPO初始化的代码就不重复贴了，这里只贴上主要的代码。
测试中构建了2个简单的类，XpoUser和XpoOrder，一对多的关系。
XpoUser
using DevExpress.Xpo;
namespace Model
{
public class XpoUser : XPObject
{
public XpoUser()
: base ()
{
// This constructor is used when an object is loaded from a persistent storage.
// Do not place any code here.
}
public XpoUser(Session session)
: base (session)
{
// This constructor is used when an object is loaded from a persistent storage.
// Do not place any code here.
}
public override void AfterConstruction()
{
base .AfterConstruction();
// Place here your initialization code.
}
private string _Name;
public string Name
{
get
{
return _Name;
}
set
{
SetPropertyValue( " Name " , ref _Name, value);
}
}
[Association( " XpoUser-Orders " )]
public XPCollection < XpoOrder > Orders
{
get
{
return GetCollection < XpoOrder > ( " Orders " );
}
}
}
}
XpoOrder
using DevExpress.Xpo;
namespace Model
{
public class XpoOrder : XPObject
{
public XpoOrder()
: base ()
{
// This constructor is used when an object is loaded from a persistent storage.
// Do not place any code here.
}
public XpoOrder(Session session)
: base (session)
{
// This constructor is used when an object is loaded from a persistent storage.
// Do not place any code here.
}
public override void AfterConstruction()
{
base .AfterConstruction();
// Place here your initialization code.
}
private string _OrderID;
public string OrderID
{
get
{
return _OrderID;
}
set
{
SetPropertyValue( " OrderID " , ref _OrderID, value);
}
}
private XpoUser _User;
[Association( " XpoUser-Orders " )]
public XpoUser User
{
get
{
return _User;
}
set
{
SetPropertyValue( " User " , ref _User, value);
}
}
}
}
做了两个测试，测试一的代码：
Test1
StringBuilder sb = new StringBuilder();
Session s1 = new Session();
Session s2 = new Session();
XpoUser user1 = new XpoUser(s1) { Name = " UserName " };
user1.Save();
XpoUser user2 = s2.FindObject < XpoUser > ( new BinaryOperator( " Name " , " UserName " ));
sb.AppendLine( string .Format( " [Session 1] User's Name : {0} " , user1.Name));
sb.AppendLine( string .Format( " [Session 2] User's Name : {0} " , user2.Name));
sb.AppendLine(Environment.NewLine + " Change user's name in Session 1 " );
user1.Name = " New UserName " ;
user1.Save();
sb.AppendLine( string .Format( " [Session 1] User's Name : {0} " , user1.Name));
sb.AppendLine( string .Format( " [Session 2] User's Name : {0} " , user2.Name));
sb.AppendLine(Environment.NewLine + " Create / Read something else(XpoRole) in Session 2 " );
XpoRole role = new XpoRole(s2) { Name = " RoleName " };
role.Save();
role = s2.FindObject < XpoRole > ( new BinaryOperator( " Name " , " RoleName " ));
sb.AppendLine( string .Format( " Role name : {0} " , role.Name));
sb.AppendLine( string .Format( " [Session 1] User's Name : {0} " , user1.Name));
sb.AppendLine( string .Format( " [Session 2] User's Name : {0} " , user2.Name));
sb.AppendLine(Environment.NewLine + " Create / Read another XpoUser in Session 2 " );
XpoUser anotherUser = new XpoUser(s2) { Name = " Another User " };
anotherUser.Save();
anotherUser = s2.FindObject < XpoUser > ( new BinaryOperator( " Name " , " Another User " ));
sb.AppendLine( string .Format( " Another user's name : {0} " , anotherUser.Name));
sb.AppendLine( string .Format( " [Session 1] User's Name : {0} " , user1.Name));
sb.AppendLine( string .Format( " [Session 2] User's Name : {0} " , user2.Name));
sb.AppendLine(Environment.NewLine + " Try to Save the user in Session 2, which is modified in Session 1 " );
try
{
user2.Save();
}
catch (Exception ex)
{
sb.AppendLine(ex.Message);
}
sb.AppendLine( string .Format( " [Session 1] User's Name : {0} " , user1.Name));
sb.AppendLine( string .Format( " [Session 2] User's Name : {0} " , user2.Name));
sb.AppendLine(Environment.NewLine + " Session.Reload(User) in Session 2 " );
s2.Reload(user2);
sb.AppendLine( string .Format( " [Session 1] User's Name : {0} " , user1.Name));
sb.AppendLine( string .Format( " [Session 2] User's Name : {0} " , user2.Name));
txtResult.Text = sb.ToString();
输出的结果：
[Session 1] User's Name : UserName
[Session 2] User's Name : UserName
Change user's name in Session 1
[Session 1] User's Name : New UserName
[Session 2] User's Name : UserName
Create / Read something else(XpoRole) in Session 2
Role name : RoleName
[Session 1] User's Name : New UserName
[Session 2] User's Name : UserName
Create / Read another XpoUser in Session 2
Another user's name : Another User
[Session 1] User's Name : New UserName
[Session 2] User's Name : UserName
Try to Save the user in Session 2, which is modified in Session 1
Cannot persist the object. It was modified or deleted (purged) by another application.
[Session 1] User's Name : New UserName
[Session 2] User's Name : UserName
Session.Reload(User) in Session 2
[Session 1] User's Name : New UserName
[Session 2] User's Name : New UserName
可以看到：
2个不同Session里Load同一个object，确实是同一个object被传递给了2个Session，而并非该Object的任何副本。
在一个Session中对该Object做了修改后，其他Session除非Reload该对象，否则将永远无法获得其他Session对其做的改动。
同时，试图保存这个已经被其他Session所更改过的对象时会抛错。
测试2：
Test2
StringBuilder sb = new StringBuilder();
Session s1 = new Session();
Session s2 = new Session();
XpoUser user1 = new XpoUser(s1) { Name = " UserName " };
XpoOrder order = new XpoOrder(s1) { OrderID = " #1 " , User = user1 };
user1.Orders.Add(order);
user1.Save();
XpoUser user2 = s2.FindObject < XpoUser > ( new BinaryOperator( " Name " , " UserName " ));
sb.AppendLine( string .Format( " [Session 1] User's Name : {0} " , user1.Name));
sb.AppendLine( string .Format( " [Session 1] User's Order : {0} " , GetOrders(user1)));
sb.AppendLine( string .Format( " [Session 2] User's Name : {0} " , user2.Name));
sb.AppendLine( string .Format( " [Session 2] User's Order : {0} " , GetOrders(user2)));
sb.AppendLine(Environment.NewLine + " Create a new order , change user's name and change Order1's ID to #3 in Session 1 " );
order = s1.FindObject < XpoOrder > ( new BinaryOperator( " OrderID " , " #1 " ));
order.OrderID = " #3 " ;
order.Save();
order = new XpoOrder(s1) { OrderID = " #2 " , User = user1 };
order.Save();
user1.Name = " New UserName " ;
user1.Orders.Add(order);
user1.Save();
sb.AppendLine( string .Format( " [Session 1] User's Name : {0} " , user1.Name));
sb.AppendLine( string .Format( " [Session 1] User's Order : {0} " , GetOrders(user1)));
sb.AppendLine( string .Format( " [Session 2] User's Name : {0} " , user2.Name));
sb.AppendLine( string .Format( " [Session 2] User's Order : {0} " , GetOrders(user2)));
sb.AppendLine(Environment.NewLine + " Session.Reload(User) in Session 2 " );
s2.Reload(user2);
sb.AppendLine( string .Format( " [Session 1] User's Name : {0} " , user1.Name));
sb.AppendLine( string .Format( " [Session 1] User's Order : {0} " , GetOrders(user1)));
sb.AppendLine( string .Format( " [Session 2] User's Name : {0} " , user2.Name));
sb.AppendLine( string .Format( " [Session 2] User's Order : {0} " , GetOrders(user2)));
sb.AppendLine(Environment.NewLine + " Session.Reload(User, forceAggregatesReload) in Session 2 " );
s2.Reload(user2, true );
sb.AppendLine( string .Format( " [Session 1] User's Name : {0} " , user1.Name));
sb.AppendLine( string .Format( " [Session 1] User's Order : {0} " , GetOrders(user1)));
sb.AppendLine( string .Format( " [Session 2] User's Name : {0} " , user2.Name));
sb.AppendLine( string .Format( " [Session 2] User's Order : {0} " , GetOrders(user2)));
sb.AppendLine(Environment.NewLine + " Load Order again in Session 2 " );
order = s2.FindObject < XpoOrder > ( new BinaryOperator( " OrderID " , " #3 " ));
sb.AppendLine( string .Format( " [Session 1] User's Name : {0} " , user1.Name));
sb.AppendLine( string .Format( " [Session 1] User's Order : {0} " , GetOrders(user1)));
sb.AppendLine( string .Format( " [Session 2] User's Name : {0} " , user2.Name));
sb.AppendLine( string .Format( " [Session 2] User's Order : {0} " , GetOrders(user2)));
sb.AppendLine(Environment.NewLine + " Session.Reload(Order, forceAggregatesReload) in Session 2 " );
s2.Reload(order, true );
sb.AppendLine( string .Format( " [Session 1] User's Name : {0} " , user1.Name));
sb.AppendLine( string .Format( " [Session 1] User's Order : {0} " , GetOrders(user1)));
sb.AppendLine( string .Format( " [Session 2] User's Name : {0} " , user2.Name));
sb.AppendLine( string .Format( " [Session 2] User's Order : {0} " , GetOrders(user2)));
sb.AppendLine(Environment.NewLine + " Load Order2 in Session 2 " );
order = s2.FindObject < XpoOrder > ( new BinaryOperator( " OrderID " , " #2 " ));
sb.AppendLine( string .Format( " [Session 1] User's Name : {0} " , user1.Name));
sb.AppendLine( string .Format( " [Session 1] User's Order : {0} " , GetOrders(user1)));
sb.AppendLine( string .Format( " [Session 2] User's Name : {0} " , user2.Name));
sb.AppendLine( string .Format( " [Session 2] User's Order : {0} " , GetOrders(user2)));
sb.AppendLine(Environment.NewLine + " Session.Reload(Order2, forceAggregatesReload) in Session 2 " );
s2.Reload(order, true );
sb.AppendLine( string .Format( " [Session 1] User's Name : {0} " , user1.Name));
sb.AppendLine( string .Format( " [Session 1] User's Order : {0} " , GetOrders(user1)));
sb.AppendLine( string .Format( " [Session 2] User's Name : {0} " , user2.Name));
sb.AppendLine( string .Format( " [Session 2] User's Order : {0} " , GetOrders(user2)));
txtResult.Text = sb.ToString();
上面代码其实测试了几种不同的情况，分别注释掉后部几个代码块单独跑可以看得更清楚，这里只贴全部跑的结果：
[Session 1] User's Name : UserName
[Session 1] User's Order : #1
[Session 2] User's Name : UserName
[Session 2] User's Order : #1
Create a new order , change user's name and change Order1's ID to #3 in Session 1
[Session 1] User's Name : New UserName
[Session 1] User's Order : #3 #2
[Session 2] User's Name : UserName
[Session 2] User's Order : #1
Session.Reload(User) in Session 2
[Session 1] User's Name : New UserName
[Session 1] User's Order : #3 #2
[Session 2] User's Name : New UserName
[Session 2] User's Order : #1
Session.Reload(User, forceAggregatesReload) in Session 2
[Session 1] User's Name : New UserName
[Session 1] User's Order : #3 #2
[Session 2] User's Name : New UserName
[Session 2] User's Order : #1
Load Order again in Session 2
[Session 1] User's Name : New UserName
[Session 1] User's Order : #3 #2
[Session 2] User's Name : New UserName
[Session 2] User's Order : #3
Session.Reload(Order, forceAggregatesReload) in Session 2
[Session 1] User's Name : New UserName
[Session 1] User's Order : #3 #2
[Session 2] User's Name : New UserName
[Session 2] User's Order : #3
Load Order2 in Session 2
[Session 1] User's Name : New UserName
[Session 1] User's Order : #3 #2
[Session 2] User's Name : New UserName
[Session 2] User's Order : #3 #2
Session.Reload(Order2, forceAggregatesReload) in Session 2
[Session 1] User's Name : New UserName
[Session 1] User's Order : #3 #2
[Session 2] User's Name : New UserName
[Session 2] User's Order : #3 #2
在这个例子里，刷新User没有获得Order的变更，刷新Order也没有获得User的变更，更没有获得同一个User下其他Order的变更。
对于有一对多关系的结构来说，无论是刷新哪个对象，用不用forceAggregatesReload，都只会刷新到自己，不会对关联对象做出更新。
是bug还是对forceAggregatesReload的理解有误？
另一个问题是，在Session下并没有找到DropCache()方法，只有一个DropIdentityMap()方法，而调用这个方法以后，再Reload其他对象会抛错（对象已被Dispose）。在DevExpress的官网上大概搜了一下，也没找到什么说法。
从上面的测试结果来看，我很同意DevExpress建议的，对每一组互相关联的少量数据都使用一个单独的Session，“大方”的使用。在保持数据之间的逻辑关系不会被破坏的情况下，颗粒度越小越好。 单一Session里包含的数据越少，则这些数据的时间跨度就越小，而且一般说来也越快会被更新。如果想彻底抛弃一个Session的缓存重新加载的话，最好就直接new一个Session来做，而不要去Drop什么的了。
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