feat(postgres): add support for reading enum types as strings

ibis/backends/postgres/__init__.py

@@ -506,6 +506,8 @@
         a = ColGen(table="a")
         c = ColGen(table="c")
         n = ColGen(table="n")
+        t = ColGen(table="t")
+        e = ColGen(table="e")
 
         format_type = self.compiler.f["pg_catalog.format_type"]
 
@@ -522,7 +524,23 @@
         type_info = (
             sg.select(
                 a.attname.as_("column_name"),
-                format_type(a.atttypid, a.atttypmod).as_("data_type"),
+                sg.case()
+                .when(
+                    sge.Exists(
+                        this=sg.select(1)
+                        .from_(sg.table("pg_type", db="pg_catalog").as_("t"))
+                        .join(
+                            sg.table("pg_enum", db="pg_catalog").as_("e"),
+                            on=sg.and_(
+                                e.enumtypid.eq(t.oid),
+                                t.typname.eq(format_type(a.atttypid, a.atttypmod)),
+                            ),
+                        )
+                    ),
+                    sge.convert("enum"),
+                )
+                .else_(format_type(a.atttypid, a.atttypmod))
+                .as_("data_type"),
                 sg.not_(a.attnotnull).as_("nullable"),
             )
             .from_(sg.table("pg_attribute", db="pg_catalog").as_("a"))

ibis/backends/postgres/tests/test_client.py

@@ -429,14 +429,18 @@
     name = gen_name("enum_table")
     with con._safe_raw_sql("CREATE TYPE mood AS ENUM ('sad', 'ok', 'happy')") as cur:
         cur.execute(f"CREATE TEMP TABLE {name} (mood mood)")
+        cur.execute(f"INSERT INTO {name} (mood) VALUES ('happy'), ('ok')")
         yield name
         cur.execute(f"DROP TABLE {name}")
         cur.execute("DROP TYPE mood")
 
 
 def test_enum_table(con, enum_table):
     t = con.table(enum_table)
-    assert t.mood.type() == dt.unknown
+    assert t.mood.type().is_string()
+    e = t.filter(t.mood == "ok")
+    result = e.execute()
+    assert len(result) == 1
 
 
 def test_parsing_oid_dtype(con):