Support postgresql enums

## Support postgresql enums

Adds support for postgresql enums, addressing
#415.

This uses the
[pg_type](https://www.postgresql.org/docs/current/catalog-pg-type.html)
and
[pg_enum](https://www.postgresql.org/docs/current/catalog-pg-enum.html)
tables to discover the valid enum values for any columns using

## Limitations

There are other [postgresql custom
types](https://www.postgresql.org/docs/current/sql-createtype.html) that
I am not attempting to support in this PR:

* composite type
* a range type
* a base type
* a shell type


## Validation

Using the enum example in the [postgres
docs](https://www.postgresql.org/docs/current/datatype-enum.html), the
integration test creates a new custom enum type, uses it in the test
table, and expects the recap `EnumType` to be found.

I also added a unit test for basically the same thing.

recap/clients/postgresql.py

@@ -90,8 +90,11 @@ def schema(self, catalog: str, schema: str, table: str) -> StructType:
             f"""
                 SELECT
                     information_schema.columns.*,
-                    pg_attribute.attndims
+                    pg_attribute.attndims,
+                    enums.enum_values
                 FROM information_schema.columns
+
+                -- Join to get the array dimensions
                 JOIN pg_catalog.pg_namespace
                     ON pg_catalog.pg_namespace.nspname = information_schema.columns.table_schema
                 JOIN pg_catalog.pg_class
@@ -100,6 +103,18 @@ def schema(self, catalog: str, schema: str, table: str) -> StructType:
                 JOIN pg_catalog.pg_attribute
                     ON pg_catalog.pg_attribute.attrelid = pg_catalog.pg_class.oid
                     AND pg_catalog.pg_attribute.attname = information_schema.columns.column_name
+
+                -- Join to get the enum values
+                LEFT JOIN pg_catalog.pg_type
+                    ON pg_catalog.pg_type.oid = pg_catalog.pg_attribute.atttypid
+                    AND pg_catalog.pg_type.typtype = 'e' -- Ensuring it's an enum type
+                LEFT JOIN (
+                    SELECT
+                        enumtypid,
+                        array_agg(enumlabel) AS enum_values
+                    FROM pg_catalog.pg_enum
+                    GROUP BY enumtypid
+                ) enums ON enums.enumtypid = pg_catalog.pg_type.oid
                 WHERE table_name = {self.param_style}
                     AND table_schema = {self.param_style}
                     AND table_catalog = {self.param_style}

recap/converters/postgresql.py

@@ -5,6 +5,7 @@
 from recap.types import (
     BoolType,
     BytesType,
+    EnumType,
     FloatType,
     IntType,
     ListType,
@@ -138,6 +139,10 @@ def _parse_type(self, column_props: dict[str, Any]) -> RecapType:
                     ),
                 )
                 self.registry.register_alias(base_type)
+        elif data_type == "user-defined" and column_props["ENUM_VALUES"]:
+            base_type = EnumType(
+                symbols=column_props["ENUM_VALUES"],
+            )
         else:
             raise ValueError(f"Unknown data type: {data_type}")
 

tests/integration/clients/test_postgresql.py

@@ -6,6 +6,7 @@
 from recap.types import (
     BoolType,
     BytesType,
+    EnumType,
     FloatType,
     IntType,
     ListType,
@@ -30,8 +31,19 @@ def setup_class(cls):
             dbname="testdb",
         )
 
-        # Create tables
+        # Create custom types
         cursor = cls.connection.cursor()
+        cursor.execute(
+            """
+            CREATE TYPE test_enum_type_mood AS ENUM (
+                'sad',
+                'ok',
+                'happy'
+            );
+            """
+        )
+
+        # Create tables
         cursor.execute(
             """
             CREATE TABLE IF NOT EXISTS test_types (
@@ -55,7 +67,8 @@ def setup_class(cls):
                 test_bit_array BIT(8)[],
                 test_not_null_array INTEGER[] NOT NULL,
                 test_int_array_2d INTEGER[][],
-                test_text_array_3d TEXT[][][]
+                test_text_array_3d TEXT[][][],
+                test_enum_mood test_enum_type_mood
             );
         """
         )
@@ -66,6 +79,7 @@ def teardown_class(cls):
         # Delete tables
         cursor = cls.connection.cursor()
         cursor.execute("DROP TABLE IF EXISTS test_types;")
+        cursor.execute("DROP TYPE IF EXISTS test_enum_type_mood;")
         cls.connection.commit()
 
         # Close the connection
@@ -266,6 +280,14 @@ def test_struct_method_arrays_no_enforce_dimensions(self):
                     ),
                 ],
             ),
+            UnionType(
+                default=None,
+                name="test_enum_mood",
+                types=[
+                    NullType(),
+                    EnumType(symbols=["sad", "ok", "happy"]),
+                ],
+            ),
         ]
         validate_results(test_types_struct, expected_fields)
 
@@ -448,6 +470,14 @@ def test_struct_method_arrays_enforce_dimensions(self):
                     ),
                 ],
             ),
+            UnionType(
+                default=None,
+                name="test_enum_mood",
+                types=[
+                    NullType(),
+                    EnumType(symbols=["sad", "ok", "happy"]),
+                ],
+            ),
         ]
         validate_results(test_types_struct, expected_fields)
 

tests/unit/converters/test_postgresql.py

@@ -4,6 +4,7 @@
 from recap.types import (
     BoolType,
     BytesType,
+    EnumType,
     FloatType,
     IntType,
     ListType,
@@ -239,6 +240,20 @@
                 scale=0,
             ),
         ),
+        (
+            {
+                "COLUMN_NAME": "test_enum",
+                "DATA_TYPE": "USER-DEFINED",
+                "CHARACTER_MAXIMUM_LENGTH": None,
+                "CHARACTER_OCTET_LENGTH": None,
+                "ENUM_VALUES": ["sad", "ok", "happy"],
+                "UDT_NAME": None,
+                "ATTNDIMS": 0,
+            },
+            EnumType(
+                symbols=["sad", "ok", "happy"],
+            ),
+        ),
     ],
 )
 def test_postgresql_converter(column_props, expected):