Please consider the following Dear software engineers imagine I have a simple ISA hierarchy: parent A with children B and C. So let's say we have the corresponding tables named "a", "b", "c" and (created with the help of the gii model creator) the classes A, B, C The following is a screenshot from MySQL workbench:

The tables b and c have a primary key which ALSO plays the role of the foreign key to the primary key of table a (as expected)

I have an attribute which are common among the children classes B and C .. BUT for other reasons (as you can see other foreign keys) I cannot move these properties to the parent class A.

Initially I names these attributes with different names. This proved to be bad design! So I got back to the database and named them with the same name "protocol"

Now to access these attributes from the parent class A you have to create a custom property inside class A.

A custom property is not a variable but a combination of get/set methods to read and write to a variable. If you have getAttr and setAttr then the attribute is named "attr".

What I did was to create a getChild method (but no setChild method was necessary) Remember the parent class (created from gii) has already access to its children from the public function relations. So exploit this to get the child object.

Note: that this solution works only if row of A has ONLY ONE child, either B or C

The goal is to create a common form to fill the database tables a and b or c So you need an attribute to differentiate the category. Is model A a parent of B or a parent of C? Once more you use custom properties. I used getCateg and setCateg methods. In my case if model A is a newRecord then the category is null but you may want to use a different solution

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-I create with the help of CHtml a drop down list so user can select B or C This drop down list has values (0, 1) which correspond to class B or C Therefore I have added to class A an array which remembers this correspondace from value => class The textfield of the dropdown list is taken from an explanation function inside class B and class C

So ok the user has chosen the class. Now I would like to have a textbox to fill the attrB and attrC in a COMMON way. I use the "activeForm" widget so I would like to keep all the functionality

Of course if I use a textbox for the model B I would have to add a SECOND textbox for the model C Above solution is not at all intuitive for the user. We would not like to have two textboxes but a SINGLE textbox.

I added an attribute named let's say "attr" inside class A to play the role for both attrB and attrC I also edited the "rules" method of class A. Now I could create a textbox based on model A. When the user submits the form the controller distinguishes from the dropdown list whether we deal with B and C. I created a protected attribute to remember the choice of B or C In that effect I created a new public method for class A where I could set this protected attribute and not only:

I use the relations to instantiate a new model B or C (for example $modelA->modelB = new modelB;)
I set the primary key of the model B (or C) according to the primary key of model A
and return the model B (or C) for further processing by the controller

So currently I use the controller to call explicitly $modelB->save() or $modelC->save(). There was an idea to override save() function in class A to automagically save the child model (since in object oriented terms the class/model A is an abstract class) Please let me know if that works better for you.