MDS Business rule regular expression to validate code to be combination of two attributes

Hi

I need to have a business rule as below:

entity1 have code, Attr1 and Attr2

I have to ensure code is always combination of Attr1 and Attr2. If either of the Attr1 or Attr2 is blank, validation should fail.

I tried below possibilities:

1. Set Code to Auto generate

2. Change tracking enabled for Attr1 and Attr2

and below BRs:

1. Attr1 has changed in group 1 AND (Attr2 has changed in group 1) then action:     Code equals a concatenated value Attr1 + Attr2

2. Attr1 is equal to Blank OR Attr2 is equal to Blank then action:     Attr1 is required
    Attr2  is required

3. Code must be unique Attr1 ,Attr2

I see BRs 1 and 2 working. I have BR 3 to fail validation in case BR1 fails resulting code to remain auto generated value.

but i dont see BR-3 working. At the end teh result is code with auto generated value validation is success.

Is there a way i can overcome this issue?

Any idea of referring attrbitues in Regular expression of this sort... to set Code equals to [Attr1] + [Attr2]?