Pickup custom length for max_length

rest_framework/utils/field_mapping.py

@@ -202,6 +202,9 @@ def get_field_kwargs(field_name, model_field):
                                    isinstance(model_field, models.TextField) or
                                    isinstance(model_field, models.FileField)):
         kwargs['max_length'] = max_length
+        custom_message = model_field.error_messages.get("max_length", None)
+        if custom_message is not None:
+            kwargs.setdefault('error_messages', {}).update(max_length=custom_message)
         validator_kwarg = [
             validator for validator in validator_kwarg
             if not isinstance(validator, validators.MaxLengthValidator)

tests/test_validators.py

@@ -2,8 +2,7 @@ import datetime
 
 import pytest
 from django.core.validators import (
-    MaxLengthValidator, MaxValueValidator, MinLengthValidator,
-    MinValueValidator
+    MaxValueValidator, MinLengthValidator, MinValueValidator
 )
 from django.db import DataError, models
 from django.test import TestCase
@@ -648,10 +647,11 @@ class ValidatorMessageTests(TestCase):
         assert s.errors['text'] == ['This is too short.']
 
     def test_max_length_validator_message_is_copied_from_model(self):
-        # Added this test because was expecting is_valid() to be false but it is not.
-        # Will investigate further
         class Post(models.Model):
-            text = models.CharField(max_length=100, validators=[MaxLengthValidator(limit_value=1, message='This is too long.')])
+            text = models.CharField(
+                max_length=1,
+                error_messages={"max_length": "This is too long"}
+            )
 
         class PostSerializer(serializers.ModelSerializer):
             class Meta:
@@ -661,3 +661,4 @@ class ValidatorMessageTests(TestCase):
         data = {'text': 'A very long text'}
         s = PostSerializer(data=data)
         assert not s.is_valid()
+        assert s.errors['text'] == ['This is too long']