Assigning Default Values to Enterprise Objects

Assignment After Insertion Into the Editing Context

If default values are intrinsic to an enterprise object, you could assign them immediately after the objects are inserted into the editing context. As an example, say your video rental application's VideoRental class has a dateCheckedOut property. You probably want to assign the current date automatically to dateCheckedOut instead of requiring the user to supply the value.

A custom enterprise object is sent certain messages when it is created, and one of these is of particular significance for assigning default values. After a custom enterprise object is created and inserted into an editing context, it receives the awakeFromInsertionInEditingContext method (which is invoked by the insertObjectWithGlobalID method which, in turn, is invoked by the insertObject method). Your enterprise object can implement the awakeFromInsertionInEditingContext method to assign default values to the attributes of the enterprise object.

 
public void awakeFromInsertionInEditingContext(EOEditingContext context) {    super.awakeFromInsertionInEditingContext(context);    dateCheckedOut = new CalendarDate();}

Use awakeFromInsertionInEditingContext method for assigning default values if you are creating objects that did not previously exist in the database. If, on the other hand, you are creating new enterprise objects from existing data in the database, you should use the awakeFromFetchInEditingContext method, which is sent to an enterprise object just created from a database row and initialized with database values. In this scenario, you must be careful about sending messages to other enterprise objects, however, because faulting may occur because the database channel might still be open while the fetching continues. Read the topics on faults for more information.

Assignment in an Action Method

If you're using a WODisplayGroup, you can implement a custom action method for the "Insert" button of your application instead of binding that control directly to the display group's insert method. In your implementation of the action method, you might create a new enterprise object, assign default values to it, and then insert the new object into the display group.

 
public void insertBook() {    EOEditingContext ec = session().defaultEditingContext();    NSDate dateCheckedOut = new NSDate();    // create new book    Book book = new Book (ec, null, null);    book.setDateCheckedOut(dateCheckedOut);    // assume display group already exists    bookDisplayGroup.insertObject(book);}

Assignment Through Default Values Per Display Group

If the default values are specific to an application or to a particular user interface, you might explicitly initialize the object in code, or specify the default values using a display group. In a Movies application, for example, your user interface may require you to provide a default value so that users can tell when they have selected a newly inserted record. In another situation, you might not want a new movie to have a default title; you might instead want the new movie's title to be blank.

To specify default values for newly created Movie objects using the display group, ( moviesDisplayGroup in the example below), you might write the following constructor for the movie page WOComponent:

 
public MoviePage() { 
    super(); 
    NSMutableDictionary defaultValues = new NSMutableDictionary(); 
    defaultValues.setObjectForKey("New Movie Title", "title"); 
    movieDisplayGroup.setInsertedObjectDefaultValues(defaultValues); 
}

This method assigns the value "New Movie Title" as the default value for a new movie's title attribute. When movieDisplayGroup inserts a new movie, it creates a new "movie" enterprise object and assigns this default title to that movie.