XAF使用数据库访问层缓存的提升性能

很多时候，为了提升性能，我们可以给数据库访问层做缓存。

以下几步可以完成这个任务:
1. 使用自定义的 XPObjectSpaceProvider
1.1. 创建自定义的 XPObjectSpaceProvider 类，派生类中需要重写CreateDataLayer 方法去创建一个 IDataLayer 对象，连接到 DataCacheNode.
1.2. 让XAF在 XafApplication.CreateCustomObjectSpaceProvider 事件中，或重写 theXafApplication.CreateDefaultObjectSpaceProvider 虚方法，文件在YourSolutionName/WxxApplication.xx 文件. 代码差不多是这样子的:

using DevExpress.ExpressApp.Xpo;
using DevExpress.Xpo;
using DevExpress.Xpo.DB;
...
public partial class SolutionWindowsFormsApplication : WxxApplication {
    //...
    protected override void CreateDefaultObjectSpaceProvider(CreateCustomObjectSpaceProviderEventArgs args) {
        args.ObjectSpaceProvider = new CachedObjectSpaceProvider(args.ConnectionString, args.Connection);
    }
}
...
public class CachedObjectSpaceProvider : XPObjectSpaceProvider {
    public CachedObjectSpaceProvider(string connectionString, IDbConnection connection)
        : base(connectionString, connection) { }
    public CachedObjectSpaceProvider(string connectionString, IDbConnection connection, bool threadSafe)
        : base(connectionString, connection, threadSafe) { }
    protected override DevExpress.Xpo.IDataLayer CreateDataLayer(IDataStore workingDataStore) {
        DataCacheRoot cacheRoot = new DataCacheRoot(workingDataStore);
        DataCacheNode cacheNode = new DataCacheNode(cacheRoot);
        if (this.threadSafe) {
            return new ThreadSafeDataLayer(this.XPDictionary, cacheNode, new Assembly[0]);
        }
        return new SimpleDataLayer(this.XPDictionary, cacheNode);
    }
}