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The Servoy platform provides a Graphical User Interface (GUI), as well as an Application Program Interface (API) which dynamically bind to database resources. This means the Servoy Application Server will dynamically generate and issue the SQL required to Read, Insert, Update and Delete database records in response to both the actions of the user and the behest of the developer.
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The fundamental unit of data binding in both the GUI and the API is the Foundset object.
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Client Cache
A Servoy client instance keeps track of which database records are in use. This is called the Client Cache and it optimizes performance by reducing the number of queries made to the database. Records are tracked by primary key. The first time the contents of a record are accessed, the Application Server must issue a query to the database on behalf of the client. The values for all of the columns of the record object are held in memory and therefore, subsequent access of the record will not produce anymore queries to the database. The user experience is greatly enhanced as one can browse quickly between forms and cached records.
A record may fall out of the cache gracefully to conserve memory and is automatically reloaded the next time it is accessed. This happens at the discretion of the client's caching engine, which is highly optimized. Relieved of the burden of managing memory, the developer can focus on more important things.
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This functionality is provided by default for all Servoy client types. There is nothing that a developer needs to do to enable it. However, the developer may augment the default functionality by implementing the Solution's onDataBroadcast event handler and invoking specific business logic.
Updating the Client Cache
What happens when data is changed outside of any Servoy client sessions?
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Fortunately, Servoy's APIs provides several opportunities to programmatically update client caches. The best approach depends on the situation.
Flush All Client Caches
This approach will re-cache all records in all client caches for a specified database table. All foundsets based on the specified table will reissue their queries and all cached records will be refreshed from the database. This approach is the most comprehensive and therefore, most expensive in terms of performance. This approach is ideal to use when:
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For more information, see the flushAllClientsCache method in the programming reference guide. |
Notify Data Change
This approach essentially sends a Data Broadcast Event to all clients. Clients are informed of changes to specific records, just as if those records were modified from within the Servoy environment. This approach is more granular than updating the entire cache for a specific table and should also yield better performance. This approach is ideal to use when:
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For more information, see the notifyDataChange method in the programming reference guide. |
Refresh Record From Database
This approach refreshes the cache for a single record or an entire foundset in the calling client only. Therefore, unlike the previous two approaches, it does not affect the cache of all clients. This approach is ideal to use when:
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