[Sqlalchemy-tickets] Issue #3813: 'on conflict ... do update ...' where clause and implicit returning (zzzeek/sqlalchemy)

[Pawel <iss...@bi...>]

New issue 3813: 'on conflict ... do update ...' where clause and implicit returning
https://bitbucket.org/zzzeek/sqlalchemy/issues/3813/on-conflict-do-update-where-clause-and

Pawel:

When using Postgres 9.5 INSERT ... ON CONFLICT ... DO UPDATE ... I get an error:

```
#!python
  File ".../sqlalchemy/orm/scoping.py", line 157, in do
    return getattr(self.registry(), name)(*args, **kwargs)
  File ".../sqlalchemy/orm/session.py", line 1044, in execute
    bind, close_with_result=True).execute(clause, params or {})
  File ".../sqlalchemy/engine/base.py", line 947, in execute
    return meth(self, multiparams, params)
  File ".../sqlalchemy/sql/elements.py", line 262, in _execute_on_connection
    return connection._execute_clauseelement(self, multiparams, params)
  File ".../sqlalchemy/engine/base.py", line 1055, in _execute_clauseelement
    compiled_sql, distilled_params
  File ".../sqlalchemy/engine/base.py", line 1204, in _execute_context
    result = context._setup_crud_result_proxy()
  File ".../sqlalchemy/engine/default.py", line 862, in _setup_crud_result_proxy
    self._setup_ins_pk_from_implicit_returning(row)
  File ".../sqlalchemy/engine/default.py", line 927, in _setup_ins_pk_from_implicit_returning
    for col in table.primary_key
TypeError: 'NoneType' object has no attribute '__getitem__'
```

I have hard time recreating issue with test (sorry I'm a bit new to the project), but i think I know what conditions cause this error.

1. INSERT must give a CONFLICT
2. ON UPDATE must have a WHERE with condition that does not allow for update
3. There should be only one data set for the INSERT VALUES (so that the implicit returning is `True` 

so sth like this should give an error:

```
#!python            
conn.execute(users.insert(), dict(id=1, name='name1'))
i = insert(users)
i = i.on_conflict_do_update(
  index_elements=[users.c.id],
  set_=dict(name=i.excluded.name),
  where=(i.excluded.name == 'other_name''))
)

conn.execute(u, [dict(id=1, name='name2')])
```

This test passes but `_implicit_returning` here is `False`. In my code I use session and `implicit_returning` is `True` (is it because of session?)  

Then in file: `sqlalchemy/engine/default.py:862` function: `_setup_crud_result_proxy`
we go inside both `if`'s and `row = result.fetchone()` sets row to `None` because of the `where` clause I think (nothing will be inserted or updated). Then the call `self._setup_ins_pk_from_implicit_returning(row)` with `row == None` give an error.
 
```
#!python
if self.isinsert:
  if self._is_implicit_returning:  # when implicit_returning is True!
    # row == None
    row = result.fetchone()
    self.returned_defaults = row
    # if row == None we get an error in this method!
    self._setup_ins_pk_from_implicit_returning(row)
    result._soft_close(_autoclose_connection=False)
    result._metadata = None
  elif not self._is_explicit_returning:
    result._soft_close(_autoclose_connection=False)
    result._metadata = None

```