Servoy 2020 Documentation
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When a user types a value into a text field (which is bound to a specific column of the database table) and clicks out, the Servoy Application Server issues a SQL update command to the database to modify the selected record. The resulting change is also broadcast\ to all connected clients.

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The fundamental unit of data binding in both the GUI and the API is the Servoy Foundset\ object.

Client Cache

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client-cacheclient-cacheA Servoy client instance keeps track of which database records are in use. This is called theClient Cacheand 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 among 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.

Data Broadcasting

What happens to the cache when the contents of a record are changed independent of the an individual client session?

Fortunately, the Servoy Application Server keeps track of all the clients and issues a Data Broadcast event to all clients whenever a record is inserted, updated or deleted by another Servoy Client. Where appropriate, each clients' cache is automatically updated and the user experiences a liveThis notification allows each client to automatically update its cache providing the end users a shared, real-time view of the data.

In a simple example, two remote users are looking at the same customer record. The first user modifies the customer's name and commits the change. The second user immediately see's the change updated in his/her client session.

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 capturing the data broadcast event and invoking specific business logic. Also, Servoy's API provides a means to programmatically update client caches in cases where a record is modified outside of a any Servoy Client session, i.e. from another application.

Panel
titleQuestion from Patrick Talbot that this chapter could answer

I remember I was thinking that there were some gray areas when it comes to datasets and foundsets, and generally how Servoy is generating the SQL from these depending on relations etc. I noticed that there were often questions about that in the forum, and no definitive answers of course (but at least pointers to what approach gives you what), and in my company too, people are coming to me quite often with some of the following questions:

  1. the 200 records loaded in a batch, and how to treat it correctly
  2. databaseManager.loadRecords() different flavors and what it does exactly
  3. how Servoy is treating DB Views (no refreshing, need to manually add the PK(s))
  4. calculations and aggregations and how/why they will deteriorate performances (what is the SQL involved especially in case of table/list forms)
  5. about dataBroadcast, how they act on foundsets but not datasets (nor foundsets based on views)
  6. dataBroadcast again: how to refresh you client's data after a batch (processor) update (maybe demonstrate the new headless_client plugin?)
  7. how to use the JSFoundsetUpdater properly, and how to efficiently update a whole foundset in one go
  8. the use of databaseManager.setCreateEmptyFormFoundsets() and what it means
  9. the advantage of using valueLists instead of relations to display related data in table/list forms
  10. how/why Servoy is sometimes creating temporary table to perform some joins
  11. generally how to interpret the performance tab in the server admin

Seems like a lot of topics in one, really, but of course not necessarily all of these topics need to be addressed, or addressed at the same time, but I really think that these are things that need more explanations/clarifications/demonstrations.

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