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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|display/DOCS/Data+Broadcasting|||||||||||||||||||||||||||||||||||||||||||||||||||||||||\ 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|display/DOCS/Foundsets+Concepts|||||||||||||||||||||||||||||||||||||||||||||||||||||||||\ object.

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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Loading Records

One of the primary jobs of a Foundset is to load records from the table to which it is bound. A Foundset object is always based on an underlying SQL query, which may change often during the lifetime of the Foundset. However the query will always take the form of selecting the Primary Key columns column(s) from the table and will also always include an Order By clause, which in its simplest form will sort the results based on the Primary Key column(s).

SELECT customerid FROM customers ORDER BY customerid ASC

After retrieving the results for Primary Key data, the Foundset will issue subsequent SQL queries to load the matching record data in smaller, optimized blocks. This query happens automatically in an on-demand fashion to satisfy the Foundset's scrollable interface. 

SELECT * FROM customers WHERE customerid IN (?,?,?,?,?,?,?,?) ORDER BY customerid ASC

The following events will modify a foundset's underlying query

• When a form to which it is bound is loaded
• When the loadRecords method is called programmatically
• When the sort definition is changed
• When it exits find mode

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Loading Records Programmatically

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The loadRecords method is used to directly modify the underlying query that loads PK data. There are several uses.

Load by a single PK
This is the simplest approach, which loads a single recordy by its primary key value.

foundset.loadRecords(123);

Load by PK data set
This approach simply dictates that a foundset will load records based on specified primary key data.

var ids = [1,2,3,6,9]; 				// an array of record PKs
var ds = databaseManager.convertToDataSet(ids); // convert the ids to a JSDataset
foundset.loadRecords(ds);			// load records

Load by another foundset
This approach is useful to essentially copy the query of another foundset.

foundset.loadRecords(anotherFoundset);

Load by Query

This approach allows a SQL query fragment to be used to set the foundset's underlying query. There are certain restriction on the form that a query can take. For obvious reasons, the query must return the primary key column(s) from the table to which the foundset is bound. For a full description see the reference guide.

var sql = 'select id from my_table where my_table.column1 in ?,?,?;
var args = [1,2,3];
foundset.loadRecords(sql, args);

Sorting

All foundsets contain a sorting definition that determines the order in which records are loaded and displayed. Sorting is always expressed in the ORDER BY clause of a foundset's query and thus handled by the database.

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