Fictional lawyer having a drink with mother and child (5,5)

'fictional lawyer' is the definition.
(I've seen this in another clue)

'a drink with mother and child' is the wordplay.
'a drink with' becomes 'perry' (I can't justify this - if you can you should give a lot more credence to this answer).
'mother' becomes 'ma' (Ma is another word for mother or mum).
'and' says to put letters next to each other.
'child' becomes 'son' (male child).
'perry'+'ma'+'son'='PERRY MASON'

'having' is the link.

Can you help me to learn more?