postgresql json aggregate

Question

I'm using postgres 9.4, I have the following query:

SELECT pid, code, name FROM activity, (
  SELECT code FROM project
) projects WHERE activity.pcode = projects.code;

which return this following relation:

pid | code |    name    
-------------------------------
  1 | p1   | activity1 
  1 | p3   | activity2
  2 | p1   | activity3
  2 | p2   | activity4
  2 | p3   | activity5

I am trying to write the same query but so that I get the project code an the activity name as a json Array relative to each "pid"

So I am looking for a query that would return something like this:

pid | json    
------------------------------------------------------------------------------------
  1 | [{'code': 'p1', 'name': 'activity1'}, {'code': 'p3', 'name': 'activity2'}] 
  2 | [{'code': 'p1', 'name': 'activity3'}, {'code': 'p2', 'name': 'activity4'}, {'code': 'p3', 'name': 'activity5'}] 

Any ideas? Thanks in advance for the help

UPDATE

Here is what I did (which is close to what Abelisto said):

SELECT pid, json_agg(json_build_object('code', code, 'name', name)) AS agg                                                                                                                                    
FROM activity JOIN (                                                                                                                                                                                          
  SELECT code FROM project                                                                                                                                                                                    
) AS p ON p.code=activity.pcode                                                                                                                                                                               
GROUP BY pid;    

Answer 1

select
  pid,
  json_agg(json_build_object('code',code,'name',name))
from
  ...
group by
  pid

Answer 2

SELECT pid from activity a, (
    select json_agg(project) from project where code = a.code 
) as p

Something like that ...