Use min_size and max_size in postgres backends

databases/backends/postgres.py

@@ -1,3 +1,4 @@
+import getpass
 import logging
 import typing
 from collections.abc import Mapping
@@ -62,7 +63,14 @@ def _get_connection_kwargs(self) -> dict:
     async def connect(self) -> None:
         assert self._pool is None, "DatabaseBackend is already running"
         kwargs = self._get_connection_kwargs()
-        self._pool = await asyncpg.create_pool(str(self._database_url), **kwargs)
+        self._pool = await asyncpg.create_pool(
+            host=self._database_url.hostname,
+            port=self._database_url.port or 5432,
+            user=self._database_url.username or getpass.getuser(),
+            password=self._database_url.password,
+            database=self._database_url.database,
+            **kwargs,
+        )
 
     async def disconnect(self) -> None:
         assert self._pool is not None, "DatabaseBackend is not running"

tests/test_connection_options.py

@@ -1,9 +1,17 @@
 """
 Unit tests for the backend connection arguments.
 """
+from contextlib import contextmanager
+from urllib.parse import urlparse
 
+import pytest
+
+from databases import Database
 from databases.backends.mysql import MySQLBackend
 from databases.backends.postgres import PostgresBackend
+from tests.test_databases import DATABASE_URLS, async_adapter
+
+POSTGRES_URLS = [url for url in DATABASE_URLS if urlparse(url).scheme == "postgresql"]
 
 
 def test_postgres_pool_size():
@@ -30,6 +38,29 @@ def test_postgres_explicit_ssl():
     assert kwargs == {"ssl": True}
 
 
+@contextmanager
+def does_not_raise():
+    yield
+
+
+urls_with_options = [
+    (f"{POSTGRES_URLS[0]}?min_size=1&max_size=20", does_not_raise()),
+    (f"{POSTGRES_URLS[0]}?min_size=0&max_size=0", pytest.raises(ValueError)),
+    (f"{POSTGRES_URLS[0]}?min_size=10&max_size=0", pytest.raises(ValueError)),
+]
+
+
+@pytest.mark.parametrize("database_url, expectation", urls_with_options)
+@async_adapter
+async def test_postgres_pool_size_connect(database_url, expectation):
+    with expectation:
+        database = Database(database_url)
+        await database.connect()
+        assert database.is_connected
+        await database.disconnect()
+        assert not database.is_connected
+
+
 def test_mysql_pool_size():
     backend = MySQLBackend("mysql://localhost/database?min_size=1&max_size=20")
     kwargs = backend._get_connection_kwargs()