Fixed #24920 -- Added support for DecimalField with no precision.

Thanks Lily for the review.

9 files changed, 105 insertions, 48 deletions

diff --git a/django/db/backends/base/features.py b/django/db/backends/base/features.py
index 2ada5177be..ecc283ff6b 100644
--- a/django/db/backends/base/features.py
+++ b/django/db/backends/base/features.py
@@ -383,6 +383,9 @@ class BaseDatabaseFeatures:
     # Does the backend support unlimited character columns?
     supports_unlimited_charfield = False
 
+    # Does the backend support numeric columns with no precision?
+    supports_no_precision_decimalfield = False
+
     # Does the backend support native tuple lookups (=, >, <, IN)?
     supports_tuple_lookups = True
 
diff --git a/django/db/backends/oracle/base.py b/django/db/backends/oracle/base.py
index 48fa01ebee..9114777030 100644
--- a/django/db/backends/oracle/base.py
+++ b/django/db/backends/oracle/base.py
@@ -106,6 +106,12 @@ class _UninitializedOperatorsDescriptor:
         return instance.__dict__["operators"]
 
 
+def _get_decimal_column(data):
+    if data["max_digits"] is None and data["decimal_places"] is None:
+        return "NUMBER"
+    return "NUMBER(%(max_digits)s, %(decimal_places)s)" % data
+
+
 class DatabaseWrapper(BaseDatabaseWrapper):
     vendor = "oracle"
     display_name = "Oracle"
@@ -125,7 +131,7 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         "CharField": "NVARCHAR2(%(max_length)s)",
         "DateField": "DATE",
         "DateTimeField": "TIMESTAMP",
-        "DecimalField": "NUMBER(%(max_digits)s, %(decimal_places)s)",
+        "DecimalField": _get_decimal_column,
         "DurationField": "INTERVAL DAY(9) TO SECOND(6)",
         "FileField": "NVARCHAR2(%(max_length)s)",
         "FilePathField": "NVARCHAR2(%(max_length)s)",
diff --git a/django/db/backends/oracle/features.py b/django/db/backends/oracle/features.py
index c07d9f1ed0..dd356181e3 100644
--- a/django/db/backends/oracle/features.py
+++ b/django/db/backends/oracle/features.py
@@ -79,6 +79,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_json_negative_indexing = False
     supports_collation_on_textfield = False
     supports_on_delete_db_default = False
+    supports_no_precision_decimalfield = True
     test_now_utc_template = "CURRENT_TIMESTAMP AT TIME ZONE 'UTC'"
     django_test_expected_failures = {
         # A bug in Django/oracledb with respect to string handling (#23843).
diff --git a/django/db/backends/oracle/introspection.py b/django/db/backends/oracle/introspection.py
index 6a0947f8ab..07b7cad840 100644
--- a/django/db/backends/oracle/introspection.py
+++ b/django/db/backends/oracle/introspection.py
@@ -194,14 +194,21 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
                 comment,
             ) = field_map[name]
             name %= {}  # oracledb, for some reason, doubles percent signs.
+            if desc[1] == oracledb.NUMBER and desc[5] == -127 and desc[4] == 0:
+                # DecimalField with no precision.
+                precision = None
+                scale = None
+            else:
+                precision = desc[4] or 0
+                scale = desc[5] or 0
             description.append(
                 FieldInfo(
                     self.identifier_converter(name),
                     desc[1],
                     display_size,
                     desc[3],
-                    desc[4] or 0,
-                    desc[5] or 0,
+                    precision,
+                    scale,
                     *desc[6:],
                     default,
                     collation,
diff --git a/django/db/backends/postgresql/base.py b/django/db/backends/postgresql/base.py
index e2728afea5..42b37ab3c2 100644
--- a/django/db/backends/postgresql/base.py
+++ b/django/db/backends/postgresql/base.py
@@ -89,6 +89,12 @@ def _get_varchar_column(data):
     return "varchar(%(max_length)s)" % data
 
 
+def _get_decimal_column(data):
+    if data["max_digits"] is None and data["decimal_places"] is None:
+        return "numeric"
+    return "numeric(%(max_digits)s, %(decimal_places)s)" % data
+
+
 class DatabaseWrapper(BaseDatabaseWrapper):
     vendor = "postgresql"
     display_name = "PostgreSQL"
@@ -105,7 +111,7 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         "CharField": _get_varchar_column,
         "DateField": "date",
         "DateTimeField": "timestamp with time zone",
-        "DecimalField": "numeric(%(max_digits)s, %(decimal_places)s)",
+        "DecimalField": _get_decimal_column,
         "DurationField": "interval",
         "FileField": "varchar(%(max_length)s)",
         "FilePathField": "varchar(%(max_length)s)",
diff --git a/django/db/backends/postgresql/features.py b/django/db/backends/postgresql/features.py
index 5bbf4b86cb..5e4ed320be 100644
--- a/django/db/backends/postgresql/features.py
+++ b/django/db/backends/postgresql/features.py
@@ -68,6 +68,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_covering_indexes = True
     supports_stored_generated_columns = True
     supports_nulls_distinct_unique_constraints = True
+    supports_no_precision_decimalfield = True
     can_rename_index = True
     test_collations = {
         "deterministic": "C",
diff --git a/django/db/backends/postgresql/introspection.py b/django/db/backends/postgresql/introspection.py
index 791d729ea4..69dd776aa3 100644
--- a/django/db/backends/postgresql/introspection.py
+++ b/django/db/backends/postgresql/introspection.py
@@ -137,8 +137,10 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
                 # display_size is always None on psycopg2.
                 line.internal_size if line.display_size is None else line.display_size,
                 line.internal_size,
-                line.precision,
-                line.scale,
+                # precision and scale are always 2^16 - 1 on psycopg2 for
+                # DecimalFields with no precision.
+                None if line.precision == 2**16 - 1 else line.precision,
+                None if line.scale == 2**16 - 1 else line.scale,
                 *field_map[line.name],
             )
             for line in cursor.description
diff --git a/django/db/backends/sqlite3/features.py b/django/db/backends/sqlite3/features.py
index 4fa6ab831b..09a0b7fc22 100644
--- a/django/db/backends/sqlite3/features.py
+++ b/django/db/backends/sqlite3/features.py
@@ -55,6 +55,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     insert_test_table_with_defaults = 'INSERT INTO {} ("null") VALUES (1)'
     supports_default_keyword_in_insert = False
     supports_unlimited_charfield = True
+    supports_no_precision_decimalfield = True
     can_return_columns_from_insert = True
     can_return_rows_from_bulk_insert = True
     can_return_rows_from_update = True
diff --git a/django/db/models/fields/__init__.py b/django/db/models/fields/__init__.py
index 3e2258e064..27d5657078 100644
--- a/django/db/models/fields/__init__.py
+++ b/django/db/models/fields/__init__.py
@@ -1725,54 +1725,84 @@ class DecimalField(Field):
         return errors
 
     def _check_decimal_places(self):
-        try:
-            decimal_places = int(self.decimal_places)
-            if decimal_places < 0:
-                raise ValueError()
-        except TypeError:
-            return [
-                checks.Error(
-                    "DecimalFields must define a 'decimal_places' attribute.",
-                    obj=self,
-                    id="fields.E130",
-                )
-            ]
-        except ValueError:
-            return [
-                checks.Error(
-                    "'decimal_places' must be a non-negative integer.",
-                    obj=self,
-                    id="fields.E131",
-                )
-            ]
+        if self.decimal_places is None:
+            if (
+                not connection.features.supports_no_precision_decimalfield
+                and "supports_no_precision_decimalfield"
+                not in self.model._meta.required_db_features
+            ):
+                return [
+                    checks.Error(
+                        "DecimalFields must define a 'decimal_places' attribute.",
+                        obj=self,
+                        id="fields.E130",
+                    )
+                ]
+            elif self.max_digits is not None:
+                return [
+                    checks.Error(
+                        "DecimalField’s max_digits and decimal_places must both "
+                        "be defined or both omitted.",
+                        obj=self,
+                        id="fields.E135",
+                    ),
+                ]
         else:
-            return []
+            try:
+                decimal_places = int(self.decimal_places)
+                if decimal_places < 0:
+                    raise ValueError()
+            except ValueError:
+                return [
+                    checks.Error(
+                        "'decimal_places' must be a non-negative integer.",
+                        obj=self,
+                        id="fields.E131",
+                    )
+                ]
+        return []
 
     def _check_max_digits(self):
-        try:
-            max_digits = int(self.max_digits)
-            if max_digits <= 0:
-                raise ValueError()
-        except TypeError:
-            return [
-                checks.Error(
-                    "DecimalFields must define a 'max_digits' attribute.",
-                    obj=self,
-                    id="fields.E132",
-                )
-            ]
-        except ValueError:
-            return [
-                checks.Error(
-                    "'max_digits' must be a positive integer.",
-                    obj=self,
-                    id="fields.E133",
-                )
-            ]
+        if self.max_digits is None:
+            if (
+                not connection.features.supports_no_precision_decimalfield
+                and "supports_no_precision_decimalfield"
+                not in self.model._meta.required_db_features
+            ):
+                return [
+                    checks.Error(
+                        "DecimalFields must define a 'max_digits' attribute.",
+                        obj=self,
+                        id="fields.E132",
+                    )
+                ]
+            elif self.decimal_places is not None:
+                return [
+                    checks.Error(
+                        "DecimalField’s max_digits and decimal_places must both "
+                        "be defined or both omitted.",
+                        obj=self,
+                        id="fields.E135",
+                    ),
+                ]
         else:
-            return []
+            try:
+                max_digits = int(self.max_digits)
+                if max_digits <= 0:
+                    raise ValueError()
+            except ValueError:
+                return [
+                    checks.Error(
+                        "'max_digits' must be a positive integer.",
+                        obj=self,
+                        id="fields.E133",
+                    )
+                ]
+        return []
 
     def _check_decimal_places_and_max_digits(self, **kwargs):
+        if self.decimal_places is None or self.max_digits is None:
+            return []
         if int(self.decimal_places) > int(self.max_digits):
             return [
                 checks.Error(