27.10 Declaratively Preventing Insert, Update, and Delete

Some 4GL tools like Oracle Forms provide declarative properties that control whether a given data collection allows inserts, updates, or deletes. While the view object does not yet support this as a built-in feature in the current release, it's easy to add this facility using a framework extension class that exploits custom metadata properties as the developer-supplied flags to control insert, update, or delete on a view object.

Note: The examples in this section refer to the DeclarativeBlockOperations project in the AdvancedViewObjectExamples workspace. See the note at the beginning of this chapter for download instructions.

To allow developers to have control over individual view object instances, you could adopt the convention of using application module custom properties by the same name as the view object instance. For example, if an application module has view object instances named ProductsInsertOnly, ProductsUpdateOnly, ProductsNoDelete, and Products, your generic code might look for application module custom properties by these same names. If the property value contains Insert, then insert is enabled for that view object instance. If the property contains Update, then update allowed. And, similarly, if the property value contains Delete, then delete is allowed. You could use helper methods like this to test for these application module properties and determine whether insert, update, and delete are allowed for a given view object:

private boolean isInsertAllowed() {
  return isStringInAppModulePropertyNamedAfterVOInstance("Insert");
}
private boolean isUpdateAllowed() {
  return isStringInAppModulePropertyNamedAfterVOInstance("Update");
}
private boolean isDeleteAllowed() {
  return isStringInAppModulePropertyNamedAfterVOInstance("Delete");
}
private boolean isStringInAppModulePropertyNamedAfterVOInstance(String s) {
  String voInstName = getViewObject().getName();
  String propVal = (String)getApplicationModule().getProperty(voInstName);
  return propVal != null ? propVal.indexOf(s) >= 0 : true;
}

Example 27-32 shows the other code required in a custom framework extension class for view rows to complete the implementation. It overrides the following methods:

• isAttributeUpdateable()

  To enable the user interface to disable fields in a new row if insert is not allowed or to disable fields in an existing row if update is not allowed.

• setAttributeInternal()

  To prevent setting attribute values in a new row if insert is not allowed or to prevent setting attributes in an existing row if update is not allowed.

• remove()

  To prevent remove if delete is not allowed.

• create()

  To prevent create if insert is not allowed.

Example 27-32 Preventing Insert, Update, or Delete Based on Custom Properties

public class CustomViewRowImpl extends ViewRowImpl {
  public boolean isAttributeUpdateable(int index) {
    if (hasEntities() && 
        ((isNewOrInitialized() && !isInsertAllowed()) ||
         (isModifiedOrUnmodified() && !isUpdateAllowed()))) {
      return false;
    }
    return super.isAttributeUpdateable(index);
  }
  protected void setAttributeInternal(int index, Object val) {
    if (hasEntities()) {
      if (isNewOrInitialized() && !isInsertAllowed())
        throw new JboException("No inserts allowed in this view");
      else if (isModifiedOrUnmodified() && !isUpdateAllowed())
        throw new JboException("No updates allowed in this view");
    }
    super.setAttributeInternal(index, val);
  }
  public void remove() {
    if (!hasEntities() || isDeleteAllowed() || isNewOrInitialized())
      super.remove();
    else
        throw new JboException("Delete not allowed in this view");
  }
  protected void create(AttributeList nvp) {
    if (isInsertAllowed()) {
      super.create(nvp);
    } else {
      throw new JboException("Insert not allowed in this view");
    }
  }
  // private helper methods omitted
}