Cached Data Store（缓存数据存储）
XPO provides functionality for a cache at the data store level. The cache stores queries and their results as they are being executed on a data store. Whenever a query, which has been executed before, passes the cache, the result from that query is returned back immediately without a roundtrip to a data store. This significantly improves performance in general and ensures that as little data as possible is transferred over the wire in distributed applications.
XPO为数据存储级别的缓存提供功能。缓存存储在数据存储上执行的查询及其结果。每当之前执行过的查询通过缓存时，该查询的结果将立即返回，而无需往返数据存储。这总体上显着提高了性能，并确保在分布式应用程序中通过网络传输的数据尽可能少。
To enable data store caching, four classes specifying the Root and its Nodes - DataCacheRoot, MSSql2005SqlDependencyCacheRoot, DataCacheNode and DataCacheNodeLocal - must be combined. The minimum setup of the cache requires one Root (DataCacheRoot or MSSql2005SqlDependencyCacheRoot) and one Node (DataCacheNode or DataCacheNodeLocal). It is possible to build cache hierarchies out of a single Root and any number of Nodes, which can be linked to the Root or another Node. This makes sense in client/server setups, when certain parts of an application need to use different settings for their data access, such as current data.
要启用数据存储缓存，必须合并指定Root及其节点的四个类——DataCacheRoot、MSSql2005SqlDependencyCacheRoot、DataCacheNode和DataCacheNodeLocal。缓存的最低设置需要一个Root（DataCacheRoot或MSSql2005SqlDependencyCacheRoot）和一个Node（DataCacheNode或DataCacheNodeLocal）。可以从单个Root和任意数量的Node构建缓存层次结构，这些节点可以链接到Root或另一个Node。这在客户端/服务器设置中是有意义的，当应用程序的某些部分需要使用不同的设置来访问数据时，例如当前数据。
The Nodes actually cache data, while the Root stores the information about table updates and synchronizes it with Nodes. To keep the table update information and cached data in sync, the Root and Nodes communicate with each other using the ICacheToCacheCommunicationCore channel. Every time a Node contacts its parent (a Root or another Node), table update information is passed in the direction from Root to Node. These regular contacts between a Node and its parent are required to keep the table information current. The latency for these contacts can be specified using the field. This field defines the maximum time that is allowed to pass before a contact to the parent becomes mandatory. So, if a Node receives a query, it first finds a cached result set for this query, and if more time than specified by has passed since its last parent contact, it will perform a quick request to its parent to synchronize table update information.
Node实际上缓存数据，而Root存储有关表更新的信息并将其与Nodes同步。为了保持表更新信息和缓存数据同步，Root和Nodes使用ICacheToCacheCommunicationCore通道相互通信。每次Node联系其父节点（Root或另一个Node）时，表更新信息都会从Root传递到Node。Node与其父节点之间的这些常规联系是保持表信息最新的必要条件。可以使用DataCacheNode. MaxCacheLatency字段指定这些联系人的延迟。该字段定义了在联系父节点成为强制性之前允许传递的最长时间。因此，如果一个节点收到一个查询，它首先会为这个查询找到一个缓存的结果集，如果距离它的最后一个父级联系人已经过去了超过DataCacheNode. MaxCacheLatency指定的时间，它将向它的父级执行一个快速请求来同步表更新信息。
Note
Data store caching relies on the idea that the cache structure knows about changes being made to data. So, even in a multi-user setup, you
should make sure that all queries and updates are performed in a way
that allows them to be recognized by the cache structure. To
accomplish this, all client requests for data have to be routed
through the client-side Nodes (DataCacheNode instances) and
server-side Root (or server-side Root-Node chains). If, for any
reason, there are changes in the database that have been made without
going through the cache structure, you can use the following utility
methods.
数据存储缓存依赖于缓存结构知道对数据所做的更改的想法。因此，即使在多用户设置中，您也应该确保所有查询和更新都以允许缓存结构识别它们的方式执行。为了实现这一点，所有客户端对数据的请求都必须通过客户端节点（DataCacheNode实例）和服务器端Root（或服务器端Root-Node链）进行路由。如果出于任何原因，数据库中发生了未通过缓存结构进行的更改，您可以使用以下实用程序方法。
The method of a Root or Node (for the MSSql2005SqlDependencyCacheRoot, use its
) - To inform the
cache about specific table changes. Root或Node的DataCacheBase.
NotifyDirtyTables方法（对于MSSql2005SqlDependencyCacheRoot，使用其）-通知缓存特定的表更改A Node’s method - To synchronize the cache completely.。 Node的DataCacheNode. CatchUp方法-完全同步缓存。
Direct SQL queries and stored procedure calls are not cached. To properly adjust a cache after calls, use any of the methods listed
above. If you are using a Microsoft SQL Server (version 2005 and
later) database as a backend for a data store, you can enable the
cache hierarchy to be automatically notified about table updates using
SqlDependency (see below).
不缓存直接SQL查询和存储过程调用。要在调用后正确调整缓存，请使用上面列出的任何方法。如果您使用MicrosoftSQLServer（2005版及更高版本）数据库作为数据存储的后端，您可以使用SqlDependency自动通知缓存层次结构表更新（见下文）。
Using SqlDependency（使用SqlDependency）
SqlDependency is a Microsoft SQL Server feature (found in version 2005 and later) that allows the database server to notify a client about changes that occur in the database. You can enable the cache hierarchy to exploit this feature to be automatically notified about any changes made to a cached database (even if they are made outside the cache hierarchy). To accomplish this, do one of the following.
SqlDependency是MicrosoftSQLServer的一项功能（可在2005版及更高版本中找到），它允许数据库服务器通知客户端数据库中发生的更改。您可以启用缓存层次结构来利用此功能，自动通知对缓存数据库所做的任何更改（即使它们是在缓存层次结构之外进行的）。要实现这一点，请执行以下操作之一。
Use the MSSql2005SqlDependencyCacheRoot as the Root element in your cache hierarchy. To create the Root element, call the overloaded methods.
使用MSSql2005SqlDependencyCacheRoot作为缓存层次结构中的根元素。要创建根元素，请调用MSSql2005SqlDependencyCacheRootCreateSqlDependencyCacheRoot重载方法。
Create a cached data store provider using the MSSql2005SqlDependencyCacheRoot.CreateProviderFromString_CacheRoot or MSSql2005SqlDependencyCacheRoot.CreateProviderFromString_WithCache method. These methods automatically create a MSSql2005SqlDependencyCacheRoot instance and associate it with this provider.
使用MSSql2005SqlDependencyCacheRootCreateProviderFromString_CacheRoot或MSSql2005SqlDependencyCacheRootCreateProviderFromString_WithCache方法创建缓存数据存储提供程序。这些方法会自动创建MSSql2005SqlDependencyCacheRoot实例并将其与此提供程序相关联。
Create a cached data store provider based on connection strings returned by the MSSqlConnectionProvider.GetConnectionString2005CacheRoot or MSSqlConnectionProvider.GetConnectionString2005WithCache method. When a cached data store provider is created, a MSSql2005SqlDependencyCacheRoot instance will be automatically created and associated with this provider.
根据MSSqlConnectionProviderGetConnectionString2005CacheRoot或MSSqlConnectionProviderGetConnectionString2005WithCache方法返回的连接字符串创建缓存数据存储提供程序。创建缓存数据存储提供程序时，将自动创建MSSql2005SqlDependencyCacheRoot实例并与此提供程序关联。
C#
string connectionString = "data source=.;initial catalog=DBName;integrated security=sspi";
IDisposable[] disposeOnDisconnect;
IDataStore node = MSSql2005SqlDependencyCacheRoot.CreateProviderFromString_WithCache(
connectionString, AutoCreateOption.DatabaseAndSchema, out disposeOnDisconnect);
XPDictionary dict = new ReflectionDictionary();
dict.GetDataStoreSchema(typeof(Customer).Assembly);
XpoDefault.DataLayer = new ThreadSafeDataLayer(dict, node);
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The SqlDependency feature is resource-demanding - every time a change happens in a database table that is being monitored, every client subscribed to SqlDependency must be notified. It is thus recommended to have only one MSSql2005SqlDependencyCacheRoot associated with a database, publishing change notifications to all other cache hierarchy Nodes.
SqlDependency特性对资源要求很高——每次被监控的数据库表发生更改时，都必须通知订阅SqlDependency的每个客户端。因此，建议只有一个MSSql2005SqlDependencyCacheRoot与数据库关联，将更改通知发布到所有其他缓存层次结构节点。
To learn about prerequisites for the SqlDependency feature use, refer to the Special Considerations When Using Query Notifications MSDN article.
要了解使用SqlDependency功能的先决条件，请参阅使用查询通知MSDN时的特殊注意事项一文。
Cache Configuration Settings（缓存配置设置）
With cache configuration settings, you can easily configure the caching scope for Nodes by designating tables to be cached. Since there is no need to cache tables that are frequently changed, you can exclude them from the caching scope using configuration settings. To specify the settings, use the Root’s method. For the MSSql2005SqlDependencyCacheRoot, use the corresponding overloaded method.
使用缓存配置设置，您可以通过指定要缓存的表来轻松配置Nodes的缓存范围。由于不需要缓存经常更改的表，因此您可以使用配置设置将它们从缓存范围中排除。要指定设置，请使用Root的DataCacheBase.配置方法。对于MSSql2005SqlDependencyCacheRoot，请使用相应的MSSql2005SqlDependencyCacheRootCreateSqlDependencyCacheRoot重载方法。
Connecting to Cached Data Stores in Distributed Applications（连接到分布式应用程序中的缓存数据存储）
You can publish cached data stores (ICachedDataStore implementers) in your distributed applications. When your client application connects to a cached data store using either the http://host:port/ or ://host:port/servicename connection string format, XPO automatically creates a Node (a DataCacheNode object) on the client. You can then create any number of Nodes and Node chains on the client, and link them to this Node to create a cache hierarchy. If you exploit the SqlDependency feature in your cached data store, the resulting distributed application setup will benefit from change notifications on the database server without great resource requirements.
您可以在分布式应用程序中发布缓存数据存储（ICachedDataStore实现器）。当您的客户端应用程序使用http：//host： port/或net.tcp：//host：port/servicename连接字符串格式连接到缓存数据存储时，XPO会自动在客户端上创建一个节点（DataCacheNode对象）。然后，您可以在客户端上创建任意数量的节点和节点链，并将它们链接到此节点以创建缓存层次结构。如果您利用缓存数据存储中的SqlDependency功能，生成的分布式应用程序设置将受益于数据库服务器上的更改通知，而无需大量资源。
On the service side, we recommend creating the DataCacheRoot only. Normally, a service that utilizes the CachedDataStoreService class should be published on the same machine or in the same local network with the database server. In this configuration, traffic between the service and the database should not significantly affect performance, and usually it is not necessary to cache these queries. However, some applications may perform many heavy queries with aggregations or grouping, and these operations may take significant time on the database side. We provide a DataCacheNode descendant for this situation - DataCacheNodeLocal. If your application performs many select operations with grouping and aggregations, check if using this class in the service application benefits performance.
在服务端，我们建议仅创建DataCacheRoot。通常，使用CachedDataStoreService类的服务应该发布在与数据库服务器相同的机器上或同一本地网络中。在这种配置中，服务和数据库之间的流量不应该显著影响性能，通常不需要缓存这些查询。但是，一些应用程序可能会执行许多带有聚合或分组的繁重查询，这些操作可能会在数据库端花费大量时间。我们为这种情况提供了一个DataCacheNode后代——DataCacheNodeLocal。如果您的应用程序执行许多带有分组和聚合的选择操作，请检查在服务应用程序中使用此类是否有利于性能。
Note
You can try the functionality described here in the Connecting to a Data Store | Data Caching section of the XPO Tutorials demo
(C:\Users\Public\Documents\DevExpress Demos
24.1\Components\WinForms\Bin\). 您可以尝试XPO教程演示（C：\User\Public\Documents\DevExpress Demos
24.1\Components\WinForms\bin\XpoTutorials. exe）的连接到数据存储|数据缓存部分中描述的功能。