DM-51676: Add support for validating units using VOUnit format

docs/changes/DM-51676.feature.rst

@@ -0,0 +1,2 @@
+Added support for validating units using VOUnit format.
+This can be enabled by using the ``--check-vounit`` flag from the command line.

python/felis/cli.py

@@ -349,6 +349,12 @@ def init_tap_schema(
     help="Check that at least one column per table is flagged as TAP principal",
     default=False,
 )
+@click.option(
+    "--check-vounit",
+    is_flag=True,
+    help="Validate unit fields using the 'vounit' format",
+    default=False,
+)
 @click.argument("files", nargs=-1, type=click.File())
 @click.pass_context
 def validate(
@@ -357,6 +363,7 @@ def validate(
     check_redundant_datatypes: bool,
     check_tap_table_indexes: bool,
     check_tap_principal: bool,
+    check_vounit: bool,
     files: Iterable[IO[str]],
 ) -> None:
     """Validate one or more felis YAML files.
@@ -371,6 +378,8 @@ def validate(
         Check that every table has a unique TAP table index.
     check_tap_principal
         Check that at least one column per table is flagged as TAP principal.
+    check_vounit
+        Validate unit fields using the 'vounit' format.
     files
         The Felis YAML files to validate.
 
@@ -398,6 +407,7 @@ def validate(
                     "check_redundant_datatypes": check_redundant_datatypes,
                     "check_tap_table_indexes": check_tap_table_indexes,
                     "check_tap_principal": check_tap_principal,
+                    "check_vounit": check_vounit,
                     "id_generation": ctx.obj["id_generation"],
                 },
             )

python/felis/datamodel.py

@@ -85,6 +85,33 @@
 """Type for a description, which must be three or more characters long."""
 
 
+def _context(info: ValidationInfo, key: str, default: bool = False) -> bool:
+    """Get a value from the validation context.
+
+    Parameters
+    ----------
+    info
+        Validation context.
+    key
+        Key to look up in the context.
+    default
+        Default value to return if the key is not found. All context values
+        currently in use are boolean, so this should be set to `False` or
+        `True`.
+
+    Notes
+    -----
+    Since all of the current context values are boolean, this function will
+    return a default of `False` if the key is not found or if there is no
+    context available. Should the context parameters be changed in the future
+    to allow for more complex values, this function will need to be updated to
+    handle those cases.
+    """
+    if info.context:
+        return info.context.get(key, default)
+    return False
+
+
 class BaseObject(BaseModel):
     """Base model.
 
@@ -279,10 +306,15 @@ def check_ivoa_ucd(cls, ivoa_ucd: str) -> str:
         return validate_ivoa_ucd(ivoa_ucd)
 
     @model_validator(mode="after")
-    def check_units(self) -> Column:
+    def check_units(self, info: ValidationInfo) -> Column:
         """Check that the ``fits:tunit`` or ``ivoa:unit`` field has valid
         units according to astropy. Only one may be provided.
 
+        Parameters
+        ----------
+        info
+            Validation context used to determine if the check is enabled.
+
         Returns
         -------
         `Column`
@@ -296,14 +328,21 @@ def check_units(self) -> Column:
         """
         fits_unit = self.fits_tunit
         ivoa_unit = self.ivoa_unit
+        check_vounit = _context(info, "check_vounit", False)
 
         if fits_unit and ivoa_unit:
             raise ValueError("Column cannot have both FITS and IVOA units")
         unit = fits_unit or ivoa_unit
 
         if unit is not None:
             try:
-                units.Unit(unit)
+                if check_vounit:
+                    # Enable IVOA unit validation
+                    logger.debug(f"Checking 'vounit' format for column '{self.name}' with value '{unit}'")
+                    units.Unit(unit, format="vounit")
+                else:
+                    # Use astropy's default unit validation
+                    units.Unit(unit)
             except ValueError as e:
                 raise ValueError(f"Invalid unit: {e}")
 

tests/data/test_vounit.yaml

@@ -0,0 +1,8 @@
+name: vounit_test
+description: Schema for testing VOUnit checks
+tables:
+  - name: test_table
+    columns:
+      - name: test_column
+        datatype: float
+        ivoa:unit: deg_C  # Bad unit VOUnit format to trigger validation error

tests/test_cli.py

@@ -221,6 +221,15 @@ def test_dump_with_invalid_file_extension_error(self) -> None:
         """Test for ``dump`` command with JSON output."""
         run_cli(["dump", TEST_YAML, "out.bad"], expect_error=True)
 
+    def test_check_vounit(self) -> None:
+        """Test for the `--check-vounit` option."""
+        # The test schema contains a column with an invalid VOUnit, so
+        # validation should fail.
+        run_cli(
+            ["validate", "--check-vounit", os.path.join(TEST_DIR, "data", "test_vounit.yml")],
+            expect_error=True,
+        )
+
 
 if __name__ == "__main__":
     unittest.main()

tests/test_datamodel.py

@@ -237,6 +237,31 @@ def test_timestamp(self) -> None:
         col = Column(name="testColumn", id="#test_col_id", datatype="timestamp")
         self.assertEqual(col.votable_xtype, "timestamp")
 
+    def test_check_vounit(self) -> None:
+        """Test validation of the 'vounit' format."""
+        # Check that a valid VOUnit is accepted when 'check_vounit' context is
+        # True.
+        col_data = {
+            "name": "testColumn",
+            "@id": "#test_col_id",
+            "datatype": "string",
+            "length": 256,
+            "ivoa:unit": "m",
+        }
+        Column.model_validate(col_data, context={"check_vounit": True})
+
+        # Check that a unit which is acceptable according to the default
+        # astropy format but not VOUnit is not accepted when the 'check_vounit'
+        # context is True.
+        invalid_col_data = col_data.copy()
+        invalid_col_data["ivoa:unit"] = "deg_C"
+        with self.assertRaises(ValidationError):
+            Column.model_validate(invalid_col_data, context={"check_vounit": True})
+
+        # Check that a unit which is valid according to the default astropy
+        # format is accepted when the 'check_vounit' context is False.
+        Column.model_validate(invalid_col_data, context={"check_vounit": False})
+
 
 class TableTestCase(unittest.TestCase):
     """Test Pydantic validation of the ``Table`` class."""