Lazy loading of fields and validators. Closes #1963.

3 files changed, 39 insertions, 23 deletions

diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index d5dccd72..8cc8e81e 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -143,7 +143,7 @@ class Field(object):
     def __init__(self, read_only=False, write_only=False,
                  required=None, default=empty, initial=empty, source=None,
                  label=None, help_text=None, style=None,
-                 error_messages=None, validators=[], allow_null=False):
+                 error_messages=None, validators=None, allow_null=False):
         self._creation_counter = Field._creation_counter
         Field._creation_counter += 1
 
@@ -166,9 +166,11 @@ class Field(object):
         self.label = label
         self.help_text = help_text
         self.style = {} if style is None else style
-        self.validators = validators[:] or self.default_validators[:]
         self.allow_null = allow_null
 
+        if validators is not None:
+            self.validators = validators[:]
+
         # These are set up by `.bind()` when the field is added to a serializer.
         self.field_name = None
         self.parent = None
@@ -214,6 +216,21 @@ class Field(object):
         else:
             self.source_attrs = self.source.split('.')
 
+    # .validators is a lazily loaded property, that gets its default
+    # value from `get_validators`.
+    @property
+    def validators(self):
+        if not hasattr(self, '_validators'):
+            self._validators = self.get_validators()
+        return self._validators
+
+    @validators.setter
+    def validators(self, validators):
+        self._validators = validators
+
+    def get_validators(self):
+        return self.default_validators[:]
+
     def get_initial(self):
         """
         Return a value to use when the field is being returned as a primitive
diff --git a/rest_framework/serializers.py b/rest_framework/serializers.py
index c9f70f2d..82e932dd 100644
--- a/rest_framework/serializers.py
+++ b/rest_framework/serializers.py
@@ -282,21 +282,23 @@ class SerializerMetaclass(type):
 
 @six.add_metaclass(SerializerMetaclass)
 class Serializer(BaseSerializer):
-    def __init__(self, *args, **kwargs):
-        super(Serializer, self).__init__(*args, **kwargs)
-
+    @property
+    def fields(self):
+        if not hasattr(self, '_fields'):
+            self._fields = BindingDict(self)
+            for key, value in self.get_fields().items():
+                self._fields[key] = value
+        return self._fields
+
+    def get_fields(self):
         # Every new serializer is created with a clone of the field instances.
         # This allows users to dynamically modify the fields on a serializer
         # instance without affecting every other serializer class.
-        self.fields = BindingDict(self)
-        for key, value in self._get_base_fields().items():
-            self.fields[key] = value
-
-        self.validators = getattr(getattr(self, 'Meta', None), 'validators', [])
-
-    def _get_base_fields(self):
         return copy.deepcopy(self._declared_fields)
 
+    def get_validators(self):
+        return getattr(getattr(self, 'Meta', None), 'validators', [])
+
     def get_initial(self):
         if self._initial_data is not None:
             return ReturnDict([
@@ -520,14 +522,6 @@ class ModelSerializer(Serializer):
     })
     _related_class = PrimaryKeyRelatedField
 
-    def __init__(self, *args, **kwargs):
-        super(ModelSerializer, self).__init__(*args, **kwargs)
-        if 'validators' not in kwargs:
-            validators = self.get_default_validators()
-            if validators:
-                self.validators.extend(validators)
-                self._kwargs['validators'] = validators
-
     def create(self, validated_attrs):
         # Check that the user isn't trying to handle a writable nested field.
         # If we don't do this explicitly they'd likely get a confusing
@@ -578,13 +572,13 @@ class ModelSerializer(Serializer):
         instance.save()
         return instance
 
-    def get_default_validators(self):
+    def get_validators(self):
         field_names = set([
             field.source for field in self.fields.values()
             if (field.source != '*') and ('.' not in field.source)
         ])
 
-        validators = []
+        validators = getattr(getattr(self, 'Meta', None), 'validators', [])
         model_class = self.Meta.model
 
         # Note that we make sure to check `unique_together` both on the
@@ -627,7 +621,7 @@ class ModelSerializer(Serializer):
 
         return validators
 
-    def _get_base_fields(self):
+    def get_fields(self):
         declared_fields = copy.deepcopy(self._declared_fields)
 
         ret = SortedDict()
diff --git a/rest_framework/utils/representation.py b/rest_framework/utils/representation.py
index 180b51f8..2a7c4675 100644
--- a/rest_framework/utils/representation.py
+++ b/rest_framework/utils/representation.py
@@ -82,6 +82,11 @@ def serializer_repr(serializer, indent, force_many=None):
             ret += field_repr(field.child_relation, force_many=field.child_relation)
         else:
             ret += field_repr(field)
+
+    if serializer.validators:
+        ret += '\n' + indent_str + 'class Meta:'
+        ret += '\n' + indent_str + '    validators = ' + smart_repr(serializer.validators)
+
     return ret