feat: In SQL targets, users can now disable column type alterations w…

…ith the `allow_column_alter` built-in setting

singer_sdk/connectors/sql.py

@@ -17,6 +17,7 @@
 from singer_sdk import typing as th
 from singer_sdk._singerlib import CatalogEntry, MetadataMapping, Schema
 from singer_sdk.exceptions import ConfigValidationError
+from singer_sdk.helpers._builtin_setting import BuiltinSetting
 from singer_sdk.helpers.capabilities import TargetLoadMethods
 
 if t.TYPE_CHECKING:
@@ -39,7 +40,10 @@ class SQLConnector:  # noqa: PLR0904
 
     allow_column_add: bool = True  # Whether ADD COLUMN is supported.
     allow_column_rename: bool = True  # Whether RENAME COLUMN is supported.
-    allow_column_alter: bool = False  # Whether altering column types is supported.
+
+    #: Whether altering column types is supported.
+    allow_column_alter = BuiltinSetting(default=True)
+
     allow_merge_upsert: bool = False  # Whether MERGE UPSERT is supported.
     allow_overwrite: bool = False  # Whether overwrite load method is supported.
     allow_temp_tables: bool = True  # Whether temp tables are supported.

singer_sdk/helpers/_builtin_setting.py

@@ -0,0 +1,51 @@
+from __future__ import annotations
+
+import typing as t
+
+T = t.TypeVar("T")
+
+
+class ConfiguredProtocol(t.Protocol):
+    """Protocol for objects with a config attribute."""
+
+    config: dict[str, t.Any]
+
+
+class BuiltinSetting(t.Generic[T]):
+    """A descriptor that gets a value from a named key of the config attribute."""
+
+    def __init__(self, custom_key: str | None = None, *, default: T | None = None):
+        """Initialize the descriptor.
+
+        Args:
+            custom_key: The key to get from the config attribute instead of the
+                attribute name.
+            default: The default value if the key is not found.
+        """
+        self.key = custom_key
+        self.default = default
+
+    def __set_name__(self, owner: type[ConfiguredProtocol], name: str) -> None:
+        """Set the name of the attribute.
+
+        Args:
+            owner: The class of the object.
+            name: The name of the attribute.
+        """
+        self.key = self.key or name
+
+    def __get__(
+        self,
+        instance: ConfiguredProtocol,
+        owner: type[ConfiguredProtocol],
+    ) -> T | None:
+        """Get the value from the instance's config attribute.
+
+        Args:
+            instance: The instance of the object.
+            owner: The class of the object.
+
+        Returns:
+            The value from the config attribute.
+        """
+        return instance.config.get(self.key, self.default)  # type: ignore[no-any-return]

singer_sdk/helpers/capabilities.py

@@ -159,6 +159,13 @@
         description="Maximum number of rows in each batch.",
     ),
 ).to_dict()
+TARGET_ALLOW_COLUMN_ALTER_CONFIG = PropertiesList(
+    Property(
+        "allow_column_alter",
+        BooleanType,
+        description="Allow altering columns in the target database.",
+    ),
+).to_dict()
 
 
 class TargetLoadMethods(str, Enum):

singer_sdk/target_base.py

@@ -18,6 +18,7 @@
 from singer_sdk.helpers.capabilities import (
     ADD_RECORD_METADATA_CONFIG,
     BATCH_CONFIG,
+    TARGET_ALLOW_COLUMN_ALTER_CONFIG,
     TARGET_BATCH_SIZE_ROWS_CONFIG,
     TARGET_HARD_DELETE_CONFIG,
     TARGET_LOAD_METHOD_CONFIG,
@@ -685,6 +686,8 @@ def _merge_missing(source_jsonschema: dict, target_jsonschema: dict) -> None:
                 if k not in target_jsonschema["properties"]:
                     target_jsonschema["properties"][k] = v
 
+        _merge_missing(TARGET_ALLOW_COLUMN_ALTER_CONFIG, config_jsonschema)
+
         capabilities = cls.capabilities
 
         if TargetCapabilities.TARGET_SCHEMA in capabilities:

tests/core/helpers/test_builtin_setting.py

@@ -0,0 +1,33 @@
+"""Test the BuiltinSetting descriptor."""
+
+from __future__ import annotations
+
+from singer_sdk.helpers._builtin_setting import BuiltinSetting
+
+
+def test_builtin_setting_descriptor():
+    class ObjWithConfig:
+        example = BuiltinSetting(default=1)
+
+        def __init__(self):
+            self.config = {"example": 1}
+
+    obj = ObjWithConfig()
+    assert obj.example == 1
+
+    obj.config["example"] = 2
+    assert obj.example == 2
+
+
+def test_builtin_setting_descriptor_custom_key():
+    class ObjWithConfig:
+        my_attr = BuiltinSetting("example", default=1)
+
+        def __init__(self):
+            self.config = {"example": 1}
+
+    obj = ObjWithConfig()
+    assert obj.my_attr == 1
+
+    obj.config["example"] = 2
+    assert obj.my_attr == 2

tests/core/targets/test_target_sql.py

@@ -48,6 +48,7 @@ class MyTarget(SQLTargetMock, capabilities=capabilities):
     about = MyTarget._get_about_info()
     default_settings = {
         "add_record_metadata",
+        "allow_column_alter",
         "load_method",
         "batch_size_rows",
     }