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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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• External changes were made using the [the Raw SQL Plugin|DOCS:rawSQL] to to update a specific database records and the primary keys are known.  *
• Another application or service was invoked from Servoy client session affecting change to specific records who's primary keys are known.

Refresh Record From Database

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Data Transactions in Servoy

Data manipulations in Servoy happen inside an in-memory transaction. When a record is created or modified, either by user action or by developer, nothing is committed to the database immediately. The Servoy Client tracks all newly-created and modified records, including which columns have changed, their former and latter values. As records are added or modified, the amount of information stored in the In-Memory transaction accrue until they are committed or rolled back. The duration of this In-Memory transaction can be short or long depending on the client's configurable Auto Save setting.

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Auto Save: ON

By default, every Servoy client is started with the Auto Save setting initialized to on/true. This means that the In-Memory transaction is typically very short as changes are committed automatically as the user navigates the client session. Specific actions like clicking in a form's area, navigating to a different form, clicking a button, etc. all trigger a save event. Auto Save is ideal for situations where the user is intended to be able to make edits freely.

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Auto Save: OFF

The developer may optionally set the Auto Save setting to off/false. This means that the length of the In-Memory transaction is controlled by the developer. As changes accrue, they are never committed until the developer programmatically invokes a save event. It is ideal to disable Auto Save for scenarios where the user is intended to perform edits in a controlled situation where a group of edits may be saved or rolled back all together.

The Auto Save setting can be programmatically changed throughout the duration of the client session to accommodate different modes for different editing scenarios.

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The Anatomy of the In-Memory Transaction

Servoy provides a robust data API, giving the developer full access to the In-Memory transaction, which consists of a listing of all record objects that were added or modified. For each of these record objects, there is a listing of every column whose value was changed. For every modified column, there is a reference to the value before and after the edit. The transaction API also allows developers to distinguish between records that are newly-created and do not yet exist in the database, versus records that already exist in the database, but have outstanding edits.

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Saving Data Changes

A developer can programmatically issue a save event, causing the contents of the In-Memory transaction to be automatically translated into instructions to insert/update database tables. A developer can optionally invoke a save event for a specific record only, leaving the rest of the transaction unaffected.

If for some reason one or more records were unable to be saved (i.e. due to a back-end database violation, etc.), the transaction will also keep track of Failed Records and their associated errors.

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Rolling Back Data Changes

A developer can programmatically issue a command to rollback the contents of the entire In-Memory transaction, causing newly created records to be removed and modified records to be reverted to their state prior to the start of the In-Memory transaction. The developer can optionally choose to rollback changes for a specific record, leaving the rest of the transaction unaffected.

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What about Deleting Records?

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.

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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.

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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.

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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 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

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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.

A foundset's sorting definition is encapsulated in a String property, which can be programmatically read using the getCurrentSort method, and written using the sort method. 

Parameters for this property include an ordered list of one or more data providers, each of which having a sort direction, either ascending or descending. The string takes a form such that each data provider and its sort direction are separated by white space. The direction is abbreviated either asc or desc. Multiple data providers are separated by commas.

Example: Sort String Format

'column1 asc, column2 desc'	// Sort on column1 ascending, then column2 desceding

The order of the data providers determines their relative priority when sorting, such that when two records contain the same value for a higher priority data provider, the sorting will be deferred the next lowest priority data provider.

Example: The following sort string will sort, first on last name, and second on first name.

foundset.sort('last_name asc, first_name asc');

The result is that all records are sorted by last name. But in the case where the last names are the same, then the first name is used.
|| last_name || first_name ||

Available Data Provider Types

The following data provider types may be used as sort criteria:

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