Refs #19884 -- Added CharField max_length introspection on Oracle.

django/db/backends/oracle/features.py

@@ -21,7 +21,6 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     has_bulk_insert = True
     supports_tablespaces = True
     supports_sequence_reset = False
-    can_introspect_max_length = False
     can_introspect_time_field = False
     atomic_transactions = False
     supports_combined_alters = False

django/db/backends/oracle/introspection.py

@@ -62,11 +62,19 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
         "Returns a description of the table, with the DB-API cursor.description interface."
         # user_tab_columns gives data default for columns
         cursor.execute("""
-            SELECT column_name, data_default
+            SELECT
+                column_name,
+                data_default,
+                CASE
+                    WHEN char_used IS NULL THEN data_length
+                    ELSE char_length
+                END as internal_size
             FROM user_tab_cols
             WHERE table_name = UPPER(%s)""", [table_name])
-        columns_default = {column: default if default != 'NULL' else None for column, default in cursor.fetchall()}
-
+        field_map = {
+            column: (internal_size, default if default != 'NULL' else None)
+            for column, default, internal_size in cursor.fetchall()
+        }
         self.cache_bust_counter += 1
         cursor.execute("SELECT * FROM {} WHERE ROWNUM < 2 AND {} > 0".format(
             self.connection.ops.quote_name(table_name),
@@ -74,9 +82,9 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
         description = []
         for desc in cursor.description:
             name = force_text(desc[0])  # cx_Oracle always returns a 'str' on both Python 2 and 3
-            default = columns_default[name]
+            internal_size, default = field_map[name]
             name = name % {}  # cx_Oracle, for some reason, doubles percent signs.
-            description.append(FieldInfo(*(name.lower(),) + desc[1:] + (default,)))
+            description.append(FieldInfo(*(name.lower(),) + desc[1:3] + (internal_size,) + desc[4:] + (default,)))
         return description
 
     def table_name_converter(self, name):

tests/inspectdb/tests.py

@@ -58,7 +58,6 @@ class InspectDBTestCase(TestCase):
         assertFieldType = self.make_field_type_asserter()
 
         # Inspecting Oracle DB doesn't produce correct results (#19884):
-        # - it gets max_length wrong: it returns a number of bytes.
         # - it reports fields as blank=True when they aren't.
         if (connection.features.can_introspect_max_length and
                 not connection.features.interprets_empty_strings_as_nulls):

tests/introspection/tests.py

@@ -83,8 +83,6 @@ class IntrospectionTests(TransactionTestCase):
              'SmallIntegerField' if connection.features.can_introspect_small_integer_field else 'IntegerField']
         )
 
-    # The following test fails on Oracle due to #17202 (can't correctly
-    # inspect the length of character columns).
     @skipUnlessDBFeature('can_introspect_max_length')
     def test_get_table_description_col_lengths(self):
         with connection.cursor() as cursor: