Refactor for a more efficient prepare_table()

Improve test_reserved_keywords() running time

target_postgres/connector.py

@@ -118,13 +118,22 @@ def prepare_table(  # type: ignore[override]
         table = meta.tables[
             full_table_name
         ]  # So we don't mess up the casing of the Table reference
+
+        columns = self.get_table_columns(
+            schema_name=schema_name, table_name=table_name, connection=connection
+        )
+
         for property_name, property_def in schema["properties"].items():
+            column_object = None
+            if property_name in columns:
+                column_object = columns[property_name]
             self.prepare_column(
                 schema_name=cast(str, schema_name),
                 table=table,
                 column_name=property_name,
                 sql_type=self.to_sql_type(property_def),
                 connection=connection,
+                column_object=column_object,
             )
 
         return meta.tables[full_table_name]
@@ -366,6 +375,7 @@ def prepare_column(  # type: ignore[override]
         column_name: str,
         sql_type: sqlalchemy.types.TypeEngine,
         connection: sqlalchemy.engine.Connection,
+        column_object: sqlalchemy.Column | None = None,
     ) -> None:
         """Adapt target table to provided schema if possible.
 
@@ -376,7 +386,11 @@ def prepare_column(  # type: ignore[override]
             sql_type: the SQLAlchemy type.
             connection: the database connection.
         """
-        if not self.column_exists(table.fullname, column_name, connection=connection):
+        column_exists = column_object is not None or self.column_exists(
+            table.fullname, column_name, connection=connection
+        )
+
+        if not column_exists:
             self._create_empty_column(
                 # We should migrate every function to use sqlalchemy.Table
                 # instead of having to know what the function wants
@@ -394,6 +408,7 @@ def prepare_column(  # type: ignore[override]
             column_name=column_name,
             sql_type=sql_type,
             connection=connection,
+            column_object=column_object,
         )
 
     def _create_empty_column(  # type: ignore[override]
@@ -466,6 +481,7 @@ def _adapt_column_type(  # type: ignore[override]
         column_name: str,
         sql_type: sqlalchemy.types.TypeEngine,
         connection: sqlalchemy.engine.Connection,
+        column_object: sqlalchemy.Column | None,
     ) -> None:
         """Adapt table column type to support the new JSON schema type.
 
@@ -477,12 +493,16 @@ def _adapt_column_type(  # type: ignore[override]
         Raises:
             NotImplementedError: if altering columns is not supported.
         """
-        current_type: sqlalchemy.types.TypeEngine = self._get_column_type(
-            schema_name=schema_name,
-            table_name=table_name,
-            column_name=column_name,
-            connection=connection,
-        )
+        current_type: sqlalchemy.types.TypeEngine
+        if column_object is not None:
+            current_type = t.cast(sqlalchemy.types.TypeEngine, column_object.type)
+        else:
+            current_type = self._get_column_type(
+                schema_name=schema_name,
+                table_name=table_name,
+                column_name=column_name,
+                connection=connection,
+            )
 
         # remove collation if present and save it
         current_type_collation = self.remove_collation(current_type)