How do I validate all my constraints in postgresql?
Well, if you need a way to check if all the foreign keys in your table are valid, this might help ( it just validates all foreign keys in your schema )

do $$
  declare r record;
BEGIN 
FOR r IN  (
  SELECT FORMAT(
    'ALTER TABLE %I VALIDATE CONSTRAINT %I;',
    tc.table_name,
    tc.constraint_name
  ) AS x
  FROM information_schema.table_constraints AS tc  
  JOIN information_schema.tables t ON t.table_name = tc.table_name and t.table_type = 'BASE TABLE' 
  JOIN information_schema.key_column_usage AS kcu ON tc.constraint_name = kcu.constraint_name 
  JOIN information_schema.constraint_column_usage AS ccu ON ccu.constraint_name = tc.constraint_name 
  WHERE  constraint_type = 'FOREIGN KEY' 
    AND tc.constraint_schema = 'public'
)
  LOOP
    EXECUTE (r.x);  
  END LOOP;
END;
$$;