BARCHART
by Joe Freeman, NeXT Systems Engineer

Overview
This palette demonstrates how to use your custom UI objects with the DBKit. It illustrates in particular the DBCustomAssociation protocol which allows you to retrieve or set values to your database via a custom view object (here the ChartOfMatrix view). Note that instead of a custom UI object, you can also connect the nib's file owner to an attribute of your DBModule, and create a custom association in this way.

Other peculiarities
When compiling this example, you'll notice the compiler warnings about conflicting declarations for the methods maxValue and minValue. This is a known problem, which will be fixed in a future release of NeXTSTEP.

How to use this example
 
Demo without DBKit
1)	Load the palette  and create a New Application.
2)	Drag a plotter into the Window.
3)	Drag off a Slider and create a matrix of Sliders.
4)	Connect  the matrix to the action method plotFromMatrix of the plotter.
5)	Go into Test Interface mode.
6)	Move the sliders and watch the bars move.
7)	End Test mode.
8)	Drag two TextFields into the window.
9)	Connect the minField and maxField outlets of the plotter to the TextFields.
10)	Go back  into TestInterface mode.
11) Move the sliders and watch the values displayed in the textfields.

Demo with DBKit using the OracleDemo.dbmodel supplied in /NextDeveloper/Examples/DatabaseKit/Models
1)	Load the palette  and create a New Application.
2)	Drag a plotter into the Window.
3)	Drag a DBModule onto the Objects icon of the NIB file.
4)	Drag a DBTableView into the Window.
5)	Select OracleDemo, Employee in the module inspector. 
6)   Connect the Employee.name and Employee.job to the DBTableView.
7)	Connect Employee.salary to the plotter.
8)	Connect the min and max outlets on the Plotter to two TextFields .
9)	Connect  the Button target  to the DBModule fetchAllRecords: method.
10)	Connect Employee.salary to a Slider.  Set the Slider min to 4000 and max to 6000 via the IB Inspector panel.
11)	Connect the Slider target to the DBModule  takeValueFrom: method.
12)	Go into TestInterface mode.
13)	Press the button to fetch all records.
14)	Select different rows in the table view and watch the colored bar move.
15)	Move the Slider and watch the colored selected bar move.
16) Mouse down on one of the bars in the graph and that row will be selected.

Topics of Interest
Besides showing you how to create a custom palette, this particular example also illustrates the use of the DBCustomAssociation protocol to make your UI object (here the custom view palette) respond to changes in the DBModule and DBFetchGroup. To make your UI object (custom view) respond to this protocol, you'll need to connect it with a DBModule attribute (here Employee.salary).
 
See File ChartOfMatrix.m for more details:

@interface Object(DBCustomAssociation)
// Called when DBModule/FetchGroup fetches a batch of new values
- associationContentsDidChange:association;

// Called when DBFetchGroup selection changes 
//	e.g., when a new record is selected in a TableView
- associationSelectionDidChange:association;

// Called when a property value changes elsewhere in the DBFetchGroup, 
//	(usually via editing in the UI) 
- association:association setValue:(DBValue *)value;

// Called when the DBFetchGroup needs to get a value,
//	e.g., when the associated UI object calls takeValueFrom:
- association:association getValue:(DBValue *)value;
@end

Last Edited -  Mai Nguyen, 18/ September /1992