From afe7ed9333e37384f8ddc57e891da9632c8714c3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jos=C3=A9=20Padilla?= <jpadilla@webapplicate.com>
Date: Tue, 9 Dec 2014 09:25:06 -0400
Subject: [PATCH] Add allow_blank for ChoiceField #2184

This makes a ChoiceField optional in HTML if
model field has `blank=True` set.
---
 rest_framework/fields.py                          |  5 +++++
 rest_framework/serializers.py                     |  2 +-
 .../rest_framework/horizontal/select.html         |  2 +-
 .../templates/rest_framework/inline/select.html   |  2 +-
 .../templates/rest_framework/vertical/select.html |  2 +-
 rest_framework/utils/field_mapping.py             | 12 ++++++------
 tests/test_fields.py                              | 15 +++++++++++++++
 7 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index 0c6c2d390..99498da73 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -958,9 +958,14 @@ class ChoiceField(Field):
             (six.text_type(key), key) for key in self.choices.keys()
         ])
 
+        self.allow_blank = kwargs.pop('allow_blank', False)
+
         super(ChoiceField, self).__init__(**kwargs)
 
     def to_internal_value(self, data):
+        if data == '' and self.allow_blank:
+            return ''
+
         try:
             return self.choice_strings_to_values[six.text_type(data)]
         except KeyError:
diff --git a/rest_framework/serializers.py b/rest_framework/serializers.py
index fb6c826b8..b0c0efa7c 100644
--- a/rest_framework/serializers.py
+++ b/rest_framework/serializers.py
@@ -942,7 +942,7 @@ class ModelSerializer(Serializer):
                     # `ModelField`, which is used when no other typed field
                     # matched to the model field.
                     kwargs.pop('model_field', None)
-                if not issubclass(field_cls, CharField):
+                if not issubclass(field_cls, CharField) and not issubclass(field_cls, ChoiceField):
                     # `allow_blank` is only valid for textual fields.
                     kwargs.pop('allow_blank', None)
 
diff --git a/rest_framework/templates/rest_framework/horizontal/select.html b/rest_framework/templates/rest_framework/horizontal/select.html
index 380b38e94..8a7fca370 100644
--- a/rest_framework/templates/rest_framework/horizontal/select.html
+++ b/rest_framework/templates/rest_framework/horizontal/select.html
@@ -4,7 +4,7 @@
     {% endif %}
     <div class="col-sm-10">
         <select class="form-control" name="{{ field.name }}">
-        {% if field.allow_null %}
+        {% if field.allow_null or field.allow_blank %}
             <option value="" {% if not field.value %}selected{% endif %}>--------</option>
         {% endif %}
         {% for key, text in field.choices.items %}
diff --git a/rest_framework/templates/rest_framework/inline/select.html b/rest_framework/templates/rest_framework/inline/select.html
index 53af2772b..6b30e4d6b 100644
--- a/rest_framework/templates/rest_framework/inline/select.html
+++ b/rest_framework/templates/rest_framework/inline/select.html
@@ -3,7 +3,7 @@
         <label class="sr-only">{{ field.label }}</label>
     {% endif %}
     <select class="form-control" name="{{ field.name }}">
-        {% if field.allow_null %}
+        {% if field.allow_null or field.allow_blank %}
             <option value="" {% if not field.value %}selected{% endif %}>--------</option>
         {% endif %}
         {% for key, text in field.choices.items %}
diff --git a/rest_framework/templates/rest_framework/vertical/select.html b/rest_framework/templates/rest_framework/vertical/select.html
index de72e1ddb..1d1109f6e 100644
--- a/rest_framework/templates/rest_framework/vertical/select.html
+++ b/rest_framework/templates/rest_framework/vertical/select.html
@@ -3,7 +3,7 @@
         <label {% if style.hide_label %}class="sr-only"{% endif %}>{{ field.label }}</label>
     {% endif %}
     <select class="form-control" name="{{ field.name }}">
-        {% if field.allow_null %}
+        {% if field.allow_null or field.allow_blank %}
             <option value="" {% if not field.value %}selected{% endif %}>--------</option>
         {% endif %}
         {% for key, text in field.choices.items %}
diff --git a/rest_framework/utils/field_mapping.py b/rest_framework/utils/field_mapping.py
index 9c187176d..86ceff314 100644
--- a/rest_framework/utils/field_mapping.py
+++ b/rest_framework/utils/field_mapping.py
@@ -91,18 +91,18 @@ def get_field_kwargs(field_name, model_field):
     if model_field.has_default() or model_field.blank or model_field.null:
         kwargs['required'] = False
 
-    if model_field.flatchoices:
-        # If this model field contains choices, then return early.
-        # Further keyword arguments are not valid.
-        kwargs['choices'] = model_field.flatchoices
-        return kwargs
-
     if model_field.null and not isinstance(model_field, models.NullBooleanField):
         kwargs['allow_null'] = True
 
     if model_field.blank:
         kwargs['allow_blank'] = True
 
+    if model_field.flatchoices:
+        # If this model field contains choices, then return early.
+        # Further keyword arguments are not valid.
+        kwargs['choices'] = model_field.flatchoices
+        return kwargs
+
     # Ensure that max_length is passed explicitly as a keyword arg,
     # rather than as a validator.
     max_length = getattr(model_field, 'max_length', None)
diff --git a/tests/test_fields.py b/tests/test_fields.py
index 135256320..3f4e65f24 100644
--- a/tests/test_fields.py
+++ b/tests/test_fields.py
@@ -804,6 +804,21 @@ class TestChoiceField(FieldValues):
         ]
     )
 
+    def test_allow_blank(self):
+        """
+        If `allow_blank=True` then '' is a valid input.
+        """
+        field = serializers.ChoiceField(
+            allow_blank=True,
+            choices=[
+                ('poor', 'Poor quality'),
+                ('medium', 'Medium quality'),
+                ('good', 'Good quality'),
+            ]
+        )
+        output = field.run_validation('')
+        assert output is ''
+
 
 class TestChoiceFieldWithType(FieldValues):
     """