How to access the User object from Account object, via the Contact object. Error: No such column 'Users' on entity 'Contact'

Question

I would like to write a SOQL query which goes from Account > Contact > User(s)

Something like this:

[SELECT PersonContactId, PersonContact.Users, PersonEmail FROM Account WHERE ...]

But I get this error:

No such column 'Users' on entity 'Contact'.

I also get this error:

No such column 'PersonContact' on entity 'Account'

But the Account object has a field called PersonContactId with a relationship name PersonContact

And the Contact object has a child relationship named: Users

So therefore, I should be able to do PersonContact.Users

Questions

1. What am I doing wrong?
2. How can I get the User collection when querying Account

Answer 1

Child relationships are only accessible by a subQuery, which means

SELECT 
  LastName, 
  (
    SELECT Id
    FROM Users
  )
FROM Contact
WHERE ...

This kind of subQueries can only happen on the top-most level of your query, hence you won't be able to get to that level from Account. Try reworking your query from Contact instead, something like

SELECT 
  LastName, 
  (
    SELECT Id
    FROM Users
  )
FROM Contact 
WHERE Id IN (
  SELECT PersonContactId 
  FROM Account 
  WHERE...)