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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 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.

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It is important to note that record deletes are not part of the In-Memory transaction. When a record is deleted, the instructions are sent to the database immediately and the delete cannot be rolled back.

The Servoy Foundset

The Servoy Foundset is a developer's window into Servoy's Data Binding layer. A single foundset always maps to a single database table and is responsible for reading from and writing to that table. From the user interface, a foundset controls which records are loaded and displayed, as well as how records are created, edited and deleted. From the developer's perspective, a foundset is a programmable object with specific behaviors and run-time properties that provide a high-level abstraction to facilitate low-level data operations.

Forms Bound to a Foundset

A Servoy Form is typically bound to a single database table and the form will always contain a single Foundset object which is bound to the same table. Much of the action in the user interface, such as a user editing data fields, directly affects the form's foundset. Conversely, actions taken on the foundset, such as programmatically editing data, is immediately reflected in the form.

Often, there can be several different forms which are bound to the same table. In most cases the forms will share the same foundset and thus provide a unified view. For example, imagine a form showing a list of customer records, where clicking on one of the records switches to another form showing a detailed view of only the selected record. The forms will automatically stay in sync and there is no need to coerce the forms to show the same record. Exceptions to this behavior include scenarios where forms are shown through different Relations, or have been explicitly marked to use a separate foundset.

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 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 columns.

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 (?,?,?,?,?,?,?,?)

Scrolling Result Set

The Foundset maintains a scrollable interface for traversing record data. This interface includes a numeric index for every record that is returned by the Foundset's query.

Foundset Size

The Foundset also has a Size property, which indicates the number of records that are indexed by the Foundset at any given time. Because the Foundset's SQL query may eventually return thousands or millions of results, the initial size of the Foundset has a maximum of 200. This value can grow dynamically, in blocks of 200, as the Foundset is traversed.

Selected Index

The Foundset maintains a Selected Index, a cursor with which to step through the records. If the selected index equals or exceeds the size of the Foundset, the Foundset will automatically issue another query to load the next batch of primary key data. Thus the Foundset loads record data and grows dynamically with the changing Selected Index property.

// Foundset size grows dynamically as the Foundset is traversed
foundset.getSize(); // returns 200
foundset.setSelectedIndex(200);
foundset.getSize(); // returns 400

Related Foundsets

Foundsets are often constrained or filtered by a Relation. In this situation, the foundset is said to be a Related Foundset and its default SQL query will include in its Where Clause, the parameters by which to constrain the foundset.

It is important to make the distinction that a relation and a foundset are not one in the same. Rather, a relation name is used to reference a specific foundset object within a given context. The context for a related foundset is always a specific record object. But for convenience, related foundsets may be referenced within a form's scripting scope and as a property of any foundset. However in these cases, the context is always implied to be the selected record in the context.

For example:

Take a predefined Relation, customers_to_orders, which models a one-to-many relationship between a customers table and an orders table. The following three lines of code, executed within the scripting scope of a form based on the customers table, all produce the same result.

// Returns the number of orders for the selected customer record in this form's foundset
customers_to_orders.getSize();

// ...the same as:
foundset.customers_to_orders.getSize();

// ...also the same as:
foundset.getSelectedRecord().customers_to_orders.getSize();

Related foundsets can be chained together using relation names. Again, the shorthand implies the context of the selected record for each foundset.

For Example:

// Returns the number of order details for the selected order record of the selected customer:
customers_to_orders.orders_to_order_details.getSize();

// ...is the same as:
customers_to_orders.getSelectedRecord().orders_to_order_details.getSelectedRecord().getSize();

Foundsets and Data Broadcasting

A Foundset may be automatically updated when the client receives a Data Broadcast Event. If the data change affected the table to which the foundset is bound, the foundset will be refreshed to reflect the change.

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