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Overview

http://developer.apple.com/documentationlegacy/mac/library/#documentation/WebObjects/Enterprise_Objects/BusinessLogic/chapter_4_section_4BusinessLogic.html

mmalcolm's StepWise article entitled "Data validation with WebObjects 5": http://www.stepwise.com/Articles/Technical/2001-06-13.01.html

Jerry W. Walker

WO and EOF have an incredible array of validation mechanisms. Here are some notes you might find helpful:

• User interface:
  • prevent/discourage user from entering inappropriate data
• Formatters:
  • formatting
    • Only accepts data with valid format
  • type coercion
    • bad type raises exception
  • simple validation
    • raises exception and ignores value
    • must be different from current value or not assigned
    • WOComponent's validationFailedWithException(Throwable t, Object value, String keyPath)
      • Called when an Enterprise Object or formatter failed validation during an assignment.
      • The default implementation ignores the error.
      • Subclassers can override to resolve the error.
• Model
  • attribute constraints
    • checks for:
      • allows null
      • string length
      • numeric precision
      • relationship integrity
    • checks these before going to DB
  • relationship integrity constraints
    • optionality
      • for both to-one & to-many
    • delete rule
      • if source deleted, then what
    • ownership, owned object is:
      • deleted if relationship broken
      • created if relationship added
    • delete rules (if user tries to delete relationship source):
      • cascade - delete all destination objects too
      • nullify - nullify back references
      • deny - prohibit delete if there are destination objects
      • nothing - delete and ignore destination objects
• EO
  • property-level (or key-level) validation
    • called when a value changes
    • default methods in superclass check model based constraints
    • can be overridden for custom validation
    • called BEFORE EO's properties have changed
    • validation methods throw exception on failure
      • validateValueForKey("weight") triggers: public <type> validateWeight(Object newWeight) throws NSValidation.ValidationException {
  • object-level validation
    • called when saving insert/delete/update changes
      • public void validateForInsert() throws NSValidation.ValidationException
      • public void validateForUpdate() throws NSValidation.ValidationException
      • public void validateForDelete() throws NSValidation.ValidationException
    • all above in superclass by default call:
      • public void validateForSave() throws NSValidation.ValidationException
    • super's implementation calls key-level validation
    • called AFTER EO's properties have changed
  • validation performed when:
    • form values are pushed into EO attributes through bindings
    • saving changes in the editing context
    • called programmatically

Checking for validation problems before calling saveChanges

You might want to display validation problems/exceptions before you try to insert/update an EO by calling saveChanges. To get the exceptions, in your component, override validationFailedWithException, with something like this:

  public void validationFailedWithException(Throwable exception, Object value, String keyPath) {
    super.validationFailedWithException(exception, value, keyPath);
    session().addError(exception.getMessage());
  }

And in Session:

  private NSMutableArray<String> _errors;

  public NSArray<String> errors() {
    return _errors.immutableClone();
  }
  
  public void setErrors(NSArray<String> errors) {
    this._errors = errors.mutableClone();
  }
  
  public void addError(String error) {
    _errors.addObject(error);
  }
  
  public boolean haveErrors() {
    return ((_errors != null) && (_errors.count() > 0))? true: false;
  }
  
  @Override
  public void awake() {
    super.awake();
    _errors = new NSMutableArray<String>();
  }

And before calling saveChanges on the editing context:

if (session().haveErrors()) {
  return null;
}
...
ec.saveChanges();

Changing an EO after Validation

...