Chore: Make default connection optional

Author: VaggelisD

sqlmesh/core/config/root.py

@@ -122,7 +122,7 @@ class Config(BaseConfig):
     """
 
     gateways: GatewayDict = {"": GatewayConfig()}
-    default_connection: SerializableConnectionConfig = DuckDBConnectionConfig()
+    default_connection: t.Optional[SerializableConnectionConfig] = None
     default_test_connection_: t.Optional[SerializableConnectionConfig] = Field(
         default=None, alias="default_test_connection"
     )
@@ -280,7 +280,11 @@ def get_gateway(self, name: t.Optional[str] = None) -> GatewayConfig:
         return self.gateways
 
     def get_connection(self, gateway_name: t.Optional[str] = None) -> ConnectionConfig:
-        return self.get_gateway(gateway_name).connection or self.default_connection
+        connection = self.get_gateway(gateway_name).connection or self.default_connection
+        if connection is None:
+            msg = f" for gateway '{gateway_name}'" if gateway_name else ""
+            raise ConfigError(f"No connection configured{msg}.")
+        return connection
 
     def get_state_connection(
         self, gateway_name: t.Optional[str] = None

tests/__init__.py

@@ -1,5 +1,26 @@
+import typing as t
+
 from sqlmesh.core import constants as c
 from sqlmesh.core.analytics import disable_analytics
+from sqlmesh.core.config import Config, DuckDBConnectionConfig
+from sqlmesh.core.config.connection import ConnectionConfig
 
 c.MAX_FORK_WORKERS = 1
 disable_analytics()
+
+
+# Replace the implementation of Config._get_connection with a new one that always
+# returns a ConnectionConfig to simplify testing
+original_get_connection = Config.get_connection
+
+
+def _lax_get_connection(self, gateway_name: t.Optional[str] = None) -> ConnectionConfig:
+    try:
+        connection = original_get_connection(self, gateway_name)
+    except:
+        connection = DuckDBConnectionConfig()
+    return connection
+
+
+setattr(Config, "original_get_connection", original_get_connection)
+setattr(Config, "get_connection", _lax_get_connection)

tests/core/test_integration.py

@@ -64,7 +64,7 @@
     SnapshotTableInfo,
 )
 from sqlmesh.utils.date import TimeLike, now, to_date, to_datetime, to_timestamp
-from sqlmesh.utils.errors import NoChangesPlanError, SQLMeshError, PlanError
+from sqlmesh.utils.errors import NoChangesPlanError, SQLMeshError, PlanError, ConfigError
 from sqlmesh.utils.pydantic import validate_string
 from tests.conftest import DuckDBMetadata, SushiDataValidator
 from tests.utils.test_helpers import use_terminal_console
@@ -6129,3 +6129,23 @@ def setup_senario(model_before: str, model_after: str):
         'Binder Error: Referenced column "this_col_does_not_exist" not found in \nFROM clause!'
         in output.stdout
     )
+
+@pytest.mark.isolated
+def test_missing_connection_config():
+    # This is the actual implementation of Config._get_connection which would be used in a real project
+    # To make testing easier, it's mocked at tests/__init__.py
+
+    with mock.patch.object(Config, "get_connection", Config.original_get_connection):
+        # Case 1: No default_connection or gateways specified should raise a ConfigError
+        with pytest.raises(ConfigError):
+            ctx = Context(config=Config())
+
+        # Case 2: No connection specified in the gateway should raise a ConfigError
+        with pytest.raises(ConfigError):
+            ctx = Context(config=Config(gateways={"default": GatewayConfig()}))
+
+        # Case 3: Specifying a default_connection or connection in the gateway should work
+        ctx = Context(config=Config(default_connection=DuckDBConnectionConfig()))
+        ctx = Context(
+            config=Config(gateways={"default": GatewayConfig(connection=DuckDBConnectionConfig())})
+        )