follow up to kvesteri#372

Co-authored-by: Nicola Soranzo <nicola.soranzo@gmail.com>

Co-authored-by: Nicola Soranzo <nicola.soranzo@gmail.com>

- postgres: return for the first positive test
- use immutable for default argument

…s/sqlalchemy-utils into topic/372-followup

Co-authored-by: Nicola Soranzo <nicola.soranzo@gmail.com>

Co-authored-by: Nicola Soranzo <nicola.soranzo@gmail.com>

- use a connection (which is closed automatically) for
  data base existence check
- explicitely use Null connection pool

already with the 1st change disposal of the engine (which closes all
open connections) is not necessary anymore. with the second change
we are completely sure.

Import _ColumnEntity from sqlalchemy.orm.context if importing from
.query fails.

And while checking if database_exists, use url.set() as URL object is
now immutable.

…*once* the version of sqlalchemy in use and deciding *once* how to change the database address. Using a wrapping function ('set_database_from_url') to simplify the code.

to set the transaction isolation level to autocommit for PostgreSQL.

Consolidate autocommit across drivers that support it, xref.
kvesteri#494 and
fix kvesteri#486 .

to use `with engine.connect()` context manager (commit
4f52578 )

when testing.

xref. kvesteri#500

Fix the following exception:

```
_____________________________________________________________________________ TestDatabasePostgresPg8000.test_create_and_drop _____________________________________________________________________________

self = <tests.functions.test_database.TestDatabasePostgresPg8000 object at 0x7f3b3da76490>, dsn = 'postgresql+pg8000://postgres:postgres@localhost/db_to_test_create_and_drop_via_pg8000_driver'

    def test_create_and_drop(self, dsn):
>       assert not database_exists(dsn)

tests/functions/test_database.py:15:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
sqlalchemy_utils/functions/database.py:488: in database_exists
    return bool(_get_scalar_result(engine, text))
sqlalchemy_utils/functions/database.py:443: in _get_scalar_result
    with engine.connect() as conn:
.venv/lib/python3.8/site-packages/sqlalchemy/engine/base.py:2263: in connect
    return self._connection_cls(self, **kwargs)
.venv/lib/python3.8/site-packages/sqlalchemy/engine/base.py:104: in __init__
    else engine.raw_connection()
.venv/lib/python3.8/site-packages/sqlalchemy/engine/base.py:2369: in raw_connection
    return self._wrap_pool_connect(
.venv/lib/python3.8/site-packages/sqlalchemy/engine/base.py:2336: in _wrap_pool_connect
    return fn()
.venv/lib/python3.8/site-packages/sqlalchemy/pool/base.py:304: in unique_connection
    return _ConnectionFairy._checkout(self)
.venv/lib/python3.8/site-packages/sqlalchemy/pool/base.py:778: in _checkout
    fairy = _ConnectionRecord.checkout(pool)
.venv/lib/python3.8/site-packages/sqlalchemy/pool/base.py:495: in checkout
    rec = pool._do_get()
.venv/lib/python3.8/site-packages/sqlalchemy/pool/impl.py:241: in _do_get
    return self._create_connection()
.venv/lib/python3.8/site-packages/sqlalchemy/pool/base.py:309: in _create_connection
    return _ConnectionRecord(self)
.venv/lib/python3.8/site-packages/sqlalchemy/pool/base.py:440: in __init__
    self.__connect(first_connect_check=True)
.venv/lib/python3.8/site-packages/sqlalchemy/pool/base.py:664: in __connect
    pool.dispatch.first_connect.for_modify(
.venv/lib/python3.8/site-packages/sqlalchemy/event/attr.py:314: in exec_once_unless_exception
    self._exec_once_impl(True, *args, **kw)
.venv/lib/python3.8/site-packages/sqlalchemy/event/attr.py:285: in _exec_once_impl
    self(*args, **kw)
.venv/lib/python3.8/site-packages/sqlalchemy/event/attr.py:322: in __call__
    fn(*args, **kw)
.venv/lib/python3.8/site-packages/sqlalchemy/util/langhelpers.py:1406: in go
    return once_fn(*arg, **kw)
.venv/lib/python3.8/site-packages/sqlalchemy/engine/strategies.py:199: in first_connect
    dialect.initialize(c)
.venv/lib/python3.8/site-packages/sqlalchemy/dialects/postgresql/pg8000.py:215: in initialize
    super(PGDialect_pg8000, self).initialize(connection)
.venv/lib/python3.8/site-packages/sqlalchemy/dialects/postgresql/base.py:2624: in initialize
    super(PGDialect, self).initialize(connection)
.venv/lib/python3.8/site-packages/sqlalchemy/engine/default.py:311: in initialize
    self.server_version_info = self._get_server_version_info(
.venv/lib/python3.8/site-packages/sqlalchemy/dialects/postgresql/base.py:2869: in _get_server_version_info
    v = connection.execute("select version()").scalar()
.venv/lib/python3.8/site-packages/sqlalchemy/engine/base.py:1003: in execute
    return self._execute_text(object_, multiparams, params)
.venv/lib/python3.8/site-packages/sqlalchemy/engine/base.py:1172: in _execute_text
    ret = self._execute_context(
.venv/lib/python3.8/site-packages/sqlalchemy/engine/base.py:1316: in _execute_context
    self._handle_dbapi_exception(
.venv/lib/python3.8/site-packages/sqlalchemy/engine/base.py:1514: in _handle_dbapi_exception
    util.raise_(exc_info[1], with_traceback=exc_info[2])
.venv/lib/python3.8/site-packages/sqlalchemy/util/compat.py:182: in raise_
    raise exception
.venv/lib/python3.8/site-packages/sqlalchemy/engine/base.py:1294: in _execute_context
    result = context._setup_crud_result_proxy()
.venv/lib/python3.8/site-packages/sqlalchemy/engine/default.py:1258: in _setup_crud_result_proxy
    result = self.get_result_proxy()
.venv/lib/python3.8/site-packages/sqlalchemy/engine/default.py:1233: in get_result_proxy
    return result.ResultProxy(self)
.venv/lib/python3.8/site-packages/sqlalchemy/engine/result.py:775: in __init__
    self._init_metadata()
.venv/lib/python3.8/site-packages/sqlalchemy/engine/result.py:807: in _init_metadata
    self._metadata = ResultMetaData(self, cursor_description)
.venv/lib/python3.8/site-packages/sqlalchemy/engine/result.py:290: in __init__
    raw = self._merge_cursor_description(
.venv/lib/python3.8/site-packages/sqlalchemy/engine/result.py:496: in _merge_cursor_description
    return [
.venv/lib/python3.8/site-packages/sqlalchemy/engine/result.py:496: in <listcomp>
    return [
.venv/lib/python3.8/site-packages/sqlalchemy/engine/result.py:616: in _merge_cols_by_none
    for (
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <sqlalchemy.engine.result.ResultMetaData object at 0x7f3b3daa4a90>, context = <sqlalchemy.dialects.postgresql.pg8000.PGExecutionContext_pg8000 object at 0x7f3b3dda7100>
cursor_description = [('version', 25, None, None, None, None, ...)]

    def _colnames_from_description(self, context, cursor_description):
        """Extract column names and data types from a cursor.description.

        Applies unicode decoding, column translation, "normalization",
        and case sensitivity rules to the names based on the dialect.

        """

        dialect = context.dialect
        case_sensitive = dialect.case_sensitive
        translate_colname = context._translate_colname
        description_decoder = (
            dialect._description_decoder
            if dialect.description_encoding
            else None
        )
        normalize_name = (
            dialect.normalize_name if dialect.requires_name_normalize else None
        )
        untranslated = None

        self.keys = []

        for idx, rec in enumerate(cursor_description):
            colname = rec[0]
            coltype = rec[1]

            if description_decoder:
>               colname = description_decoder(colname)
E               TypeError: expected bytes, str found

.venv/lib/python3.8/site-packages/sqlalchemy/engine/result.py:545: TypeError
```

…_registry'`

and similar messages for other objects.

…'_mapper_registry'`

Fix errors:

```
    def make_order_by_deterministic(query):
        """

        order_by_func = sa.asc

>       if not query._order_by:
E       AttributeError: 'Query' object has no attribute '_order_by'

```

```
tests/functions/test_make_order_by_deterministic.py:74:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

query = <sqlalchemy.orm.query.Query object at 0x7f03d5af64f0>

    def make_order_by_deterministic(query):

                else:
                    order_by_func = sa.asc
>               column = order_by.get_children()[0]
E               TypeError: 'itertools.chain' object is not subscriptable
```

…eate()`

Co-authored-by: Nicola Soranzo <nicola.soranzo@gmail.com>

This returns a `Subquery` object which is not executable in SQLAlchemy 1.4:

```
tests/relationships/test_select_correlated_expression.py:399:
    assert session.execute(aggregate)
.venv/lib/python3.8/site-packages/sqlalchemy/orm/session.py:1587: in execute
    statement = coercions.expect(roles.StatementRole, statement)
.venv/lib/python3.8/site-packages/sqlalchemy/sql/coercions.py:200: in expect
    return impl._implicit_coercions(
.venv/lib/python3.8/site-packages/sqlalchemy/sql/coercions.py:836: in _implicit_coercions
    return super(StatementImpl, self)._implicit_coercions(
.venv/lib/python3.8/site-packages/sqlalchemy/sql/coercions.py:242: in _implicit_coercions
    self._raise_for_expected(element, argname, resolved)
.venv/lib/python3.8/site-packages/sqlalchemy/sql/coercions.py:270: in _raise_for_expected
    util.raise_(exc.ArgumentError(msg, code=code), replace_context=err)

E           sqlalchemy.exc.ArgumentError: Executable SQL or text() construct expected, got <sqlalchemy.sql.selectable.Subquery at 0x7fb34b5e1880; test>.
```

The sort_query and get_query_entities functions never worked fully as intended and
contained lots of quirky  edge cases:

1. sort_query function was dangerous in a sense that it could be used for really
inefficient queries (sorting by non-indexed column).
2. The entity string label introspection in both functions relied on SQLAlchemy internals
which were drastically changed in SA 1.4. Relying on those was never a good idea in
the first place.

which depends on `get_query_entities()` which was removed in commit
460e1da .

Co-authored-by: Nicola Soranzo <nicola.soranzo@gmail.com>

Remove `!` from password so `SA_PASSWORD` doesn't need extra quotes.

Change EncryptedType tests to use StringEncryptedType