I've two custom modules say A and B.

A module has some fields and B has some fields. Now I want to populate the fields from B module to A module which are common in both using a lookup field in my A module.

I've tried this . But this is only for default modules and not custom modules. hydrogen water maker

I want to write a function for a single case. B module has a text field with label called b and A module also have a text field with label called b. I want to populate the text field value of A module with that of B module.