django/tests/serializers/tests.py

# -*- coding: utf-8 -*-
from __future__ import unicode_literals

import importlib
import json
import re
import unittest
from datetime import datetime
from xml.dom import minidom

from django.core import management, serializers
from django.db import connection, transaction
from django.test import (
    SimpleTestCase, TestCase, TransactionTestCase, mock, override_settings,
    skipUnlessDBFeature,
)
from django.test.utils import Approximate
from django.utils import six
from django.utils.six import StringIO

from .models import (
    Actor, Article, Author, AuthorProfile, Category, Movie, Player, Score,
    Team,
)

try:
    import yaml
    HAS_YAML = True
except ImportError:
    HAS_YAML = False


@override_settings(
    SERIALIZATION_MODULES={
        "json2": "django.core.serializers.json",
    }
)
class SerializerRegistrationTests(SimpleTestCase):
    def setUp(self):
        self.old_serializers = serializers._serializers
        serializers._serializers = {}

    def tearDown(self):
        serializers._serializers = self.old_serializers

    def test_register(self):
        "Registering a new serializer populates the full registry. Refs #14823"
        serializers.register_serializer('json3', 'django.core.serializers.json')

        public_formats = serializers.get_public_serializer_formats()
        self.assertIn('json3', public_formats)
        self.assertIn('json2', public_formats)
        self.assertIn('xml', public_formats)

    def test_unregister(self):
        "Unregistering a serializer doesn't cause the registry to be repopulated. Refs #14823"
        serializers.unregister_serializer('xml')
        serializers.register_serializer('json3', 'django.core.serializers.json')

        public_formats = serializers.get_public_serializer_formats()

        self.assertNotIn('xml', public_formats)
        self.assertIn('json3', public_formats)

    def test_builtin_serializers(self):
        "Requesting a list of serializer formats popuates the registry"
        all_formats = set(serializers.get_serializer_formats())
        public_formats = set(serializers.get_public_serializer_formats())

        self.assertIn('xml', all_formats),
        self.assertIn('xml', public_formats)

        self.assertIn('json2', all_formats)
        self.assertIn('json2', public_formats)

        self.assertIn('python', all_formats)
        self.assertNotIn('python', public_formats)


class SerializersTestBase(object):
    @staticmethod
    def _comparison_value(value):
        return value

    def setUp(self):
        sports = Category.objects.create(name="Sports")
        music = Category.objects.create(name="Music")
        op_ed = Category.objects.create(name="Op-Ed")

        self.joe = Author.objects.create(name="Joe")
        self.jane = Author.objects.create(name="Jane")

        self.a1 = Article(
            author=self.jane,
            headline="Poker has no place on ESPN",
            pub_date=datetime(2006, 6, 16, 11, 00)
        )
        self.a1.save()
        self.a1.categories = [sports, op_ed]

        self.a2 = Article(
            author=self.joe,
            headline="Time to reform copyright",
            pub_date=datetime(2006, 6, 16, 13, 00, 11, 345)
        )
        self.a2.save()
        self.a2.categories = [music, op_ed]

    def test_serialize(self):
        """Tests that basic serialization works."""
        serial_str = serializers.serialize(self.serializer_name,
                                           Article.objects.all())
        self.assertTrue(self._validate_output(serial_str))

    def test_serializer_roundtrip(self):
        """Tests that serialized content can be deserialized."""
        serial_str = serializers.serialize(self.serializer_name,
                                           Article.objects.all())
        models = list(serializers.deserialize(self.serializer_name, serial_str))
        self.assertEqual(len(models), 2)

    def test_altering_serialized_output(self):
        """
        Tests the ability to create new objects by
        modifying serialized content.
        """
        old_headline = "Poker has no place on ESPN"
        new_headline = "Poker has no place on television"
        serial_str = serializers.serialize(self.serializer_name,
                                           Article.objects.all())
        serial_str = serial_str.replace(old_headline, new_headline)
        models = list(serializers.deserialize(self.serializer_name, serial_str))

        # Prior to saving, old headline is in place
        self.assertTrue(Article.objects.filter(headline=old_headline))
        self.assertFalse(Article.objects.filter(headline=new_headline))

        for model in models:
            model.save()

        # After saving, new headline is in place
        self.assertTrue(Article.objects.filter(headline=new_headline))
        self.assertFalse(Article.objects.filter(headline=old_headline))

    def test_one_to_one_as_pk(self):
        """
        Tests that if you use your own primary key field
        (such as a OneToOneField), it doesn't appear in the
        serialized field list - it replaces the pk identifier.
        """
        profile = AuthorProfile(author=self.joe,
                                date_of_birth=datetime(1970, 1, 1))
        profile.save()
        serial_str = serializers.serialize(self.serializer_name,
                                           AuthorProfile.objects.all())
        self.assertFalse(self._get_field_values(serial_str, 'author'))

        for obj in serializers.deserialize(self.serializer_name, serial_str):
            self.assertEqual(obj.object.pk, self._comparison_value(self.joe.pk))

    def test_serialize_field_subset(self):
        """Tests that output can be restricted to a subset of fields"""
        valid_fields = ('headline', 'pub_date')
        invalid_fields = ("author", "categories")
        serial_str = serializers.serialize(self.serializer_name,
                                    Article.objects.all(),
                                    fields=valid_fields)
        for field_name in invalid_fields:
            self.assertFalse(self._get_field_values(serial_str, field_name))

        for field_name in valid_fields:
            self.assertTrue(self._get_field_values(serial_str, field_name))

    def test_serialize_unicode(self):
        """Tests that unicode makes the roundtrip intact"""
        actor_name = "Za\u017c\u00f3\u0142\u0107"
        movie_title = 'G\u0119\u015bl\u0105 ja\u017a\u0144'
        ac = Actor(name=actor_name)
        mv = Movie(title=movie_title, actor=ac)
        ac.save()
        mv.save()

        serial_str = serializers.serialize(self.serializer_name, [mv])
        self.assertEqual(self._get_field_values(serial_str, "title")[0], movie_title)
        self.assertEqual(self._get_field_values(serial_str, "actor")[0], actor_name)

        obj_list = list(serializers.deserialize(self.serializer_name, serial_str))
        mv_obj = obj_list[0].object
        self.assertEqual(mv_obj.title, movie_title)

    def test_serialize_superfluous_queries(self):
        """Ensure no superfluous queries are made when serializing ForeignKeys

        #17602
        """
        ac = Actor(name='Actor name')
        ac.save()
        mv = Movie(title='Movie title', actor_id=ac.pk)
        mv.save()

        with self.assertNumQueries(0):
            serializers.serialize(self.serializer_name, [mv])

    def test_serialize_with_null_pk(self):
        """
        Tests that serialized data with no primary key results
        in a model instance with no id
        """
        category = Category(name="Reference")
        serial_str = serializers.serialize(self.serializer_name, [category])
        pk_value = self._get_pk_values(serial_str)[0]
        self.assertFalse(pk_value)

        cat_obj = list(serializers.deserialize(self.serializer_name,
                                               serial_str))[0].object
        self.assertEqual(cat_obj.id, None)

    def test_float_serialization(self):
        """Tests that float values serialize and deserialize intact"""
        sc = Score(score=3.4)
        sc.save()
        serial_str = serializers.serialize(self.serializer_name, [sc])
        deserial_objs = list(serializers.deserialize(self.serializer_name,
                                                serial_str))
        self.assertEqual(deserial_objs[0].object.score, Approximate(3.4, places=1))

    def test_custom_field_serialization(self):
        """Tests that custom fields serialize and deserialize intact"""
        team_str = "Spartak Moskva"
        player = Player()
        player.name = "Soslan Djanaev"
        player.rank = 1
        player.team = Team(team_str)
        player.save()
        serial_str = serializers.serialize(self.serializer_name,
                                           Player.objects.all())
        team = self._get_field_values(serial_str, "team")
        self.assertTrue(team)
        self.assertEqual(team[0], team_str)

        deserial_objs = list(serializers.deserialize(self.serializer_name, serial_str))
        self.assertEqual(deserial_objs[0].object.team.to_string(),
                         player.team.to_string())

    def test_pre_1000ad_date(self):
        """Tests that year values before 1000AD are properly formatted"""
        # Regression for #12524 -- dates before 1000AD get prefixed
        # 0's on the year
        a = Article.objects.create(
            author=self.jane,
            headline="Nobody remembers the early years",
            pub_date=datetime(1, 2, 3, 4, 5, 6))

        serial_str = serializers.serialize(self.serializer_name, [a])
        date_values = self._get_field_values(serial_str, "pub_date")
        self.assertEqual(date_values[0].replace('T', ' '), "0001-02-03 04:05:06")

    def test_pkless_serialized_strings(self):
        """
        Tests that serialized strings without PKs
        can be turned into models
        """
        deserial_objs = list(serializers.deserialize(self.serializer_name,
                                                     self.pkless_str))
        for obj in deserial_objs:
            self.assertFalse(obj.object.id)
            obj.save()
        self.assertEqual(Category.objects.all().count(), 5)

    def test_deterministic_mapping_ordering(self):
        """Mapping such as fields should be deterministically ordered. (#24558)"""
        output = serializers.serialize(self.serializer_name, [self.a1], indent=2)
        categories = self.a1.categories.values_list('pk', flat=True)
        self.assertEqual(output, self.mapping_ordering_str % {
            'article_pk': self.a1.pk,
            'author_pk': self.a1.author_id,
            'first_category_pk': categories[0],
            'second_category_pk': categories[1],
        })

    def test_deserialize_force_insert(self):
        """Tests that deserialized content can be saved with force_insert as a parameter."""
        serial_str = serializers.serialize(self.serializer_name, [self.a1])
        deserial_obj = list(serializers.deserialize(self.serializer_name, serial_str))[0]
        with mock.patch('django.db.models.Model') as mock_model:
            deserial_obj.save(force_insert=False)
            mock_model.save_base.assert_called_with(deserial_obj.object, raw=True, using=None, force_insert=False)


class SerializersTransactionTestBase(object):

    available_apps = ['serializers']

    @skipUnlessDBFeature('supports_forward_references')
    def test_forward_refs(self):
        """
        Tests that objects ids can be referenced before they are
        defined in the serialization data.
        """
        # The deserialization process needs to run in a transaction in order
        # to test forward reference handling.
        with transaction.atomic():
            objs = serializers.deserialize(self.serializer_name, self.fwd_ref_str)
            with connection.constraint_checks_disabled():
                for obj in objs:
                    obj.save()

        for model_cls in (Category, Author, Article):
            self.assertEqual(model_cls.objects.all().count(), 1)
        art_obj = Article.objects.all()[0]
        self.assertEqual(art_obj.categories.all().count(), 1)
        self.assertEqual(art_obj.author.name, "Agnes")


class XmlSerializerTestCase(SerializersTestBase, TestCase):
    serializer_name = "xml"
    pkless_str = """<?xml version="1.0" encoding="utf-8"?>
<django-objects version="1.0">
    <object model="serializers.category">
        <field type="CharField" name="name">Reference</field>
    </object>
    <object model="serializers.category">
        <field type="CharField" name="name">Non-fiction</field>
    </object>
</django-objects>"""
    mapping_ordering_str = """<?xml version="1.0" encoding="utf-8"?>
<django-objects version="1.0">
  <object model="serializers.article" pk="%(article_pk)s">
    <field name="author" rel="ManyToOneRel" to="serializers.author">%(author_pk)s</field>
    <field name="headline" type="CharField">Poker has no place on ESPN</field>
    <field name="pub_date" type="DateTimeField">2006-06-16T11:00:00</field>
    <field name="categories" rel="ManyToManyRel" to="serializers.category"><object pk="%(first_category_pk)s"></object><object pk="%(second_category_pk)s"></object></field>
    <field name="meta_data" rel="ManyToManyRel" to="serializers.categorymetadata"></field>
  </object>
</django-objects>"""

    @staticmethod
    def _comparison_value(value):
        # The XML serializer handles everything as strings, so comparisons
        # need to be performed on the stringified value
        return six.text_type(value)

    @staticmethod
    def _validate_output(serial_str):
        try:
            minidom.parseString(serial_str)
        except Exception:
            return False
        else:
            return True

    @staticmethod
    def _get_pk_values(serial_str):
        ret_list = []
        dom = minidom.parseString(serial_str)
        fields = dom.getElementsByTagName("object")
        for field in fields:
            ret_list.append(field.getAttribute("pk"))
        return ret_list

    @staticmethod
    def _get_field_values(serial_str, field_name):
        ret_list = []
        dom = minidom.parseString(serial_str)
        fields = dom.getElementsByTagName("field")
        for field in fields:
            if field.getAttribute("name") == field_name:
                temp = []
                for child in field.childNodes:
                    temp.append(child.nodeValue)
                ret_list.append("".join(temp))
        return ret_list

    def test_control_char_failure(self):
        """
        Serializing control characters with XML should fail as those characters
        are not supported in the XML 1.0 standard (except HT, LF, CR).
        """
        self.a1.headline = "This contains \u0001 control \u0011 chars"
        msg = "Article.headline (pk:%s) contains unserializable characters" % self.a1.pk
        with self.assertRaisesMessage(ValueError, msg):
            serializers.serialize(self.serializer_name, [self.a1])
        self.a1.headline = "HT \u0009, LF \u000A, and CR \u000D are allowed"
        self.assertIn(
            "HT \t, LF \n, and CR \r are allowed",
            serializers.serialize(self.serializer_name, [self.a1])
        )


class XmlSerializerTransactionTestCase(SerializersTransactionTestBase, TransactionTestCase):
    serializer_name = "xml"
    fwd_ref_str = """<?xml version="1.0" encoding="utf-8"?>
<django-objects version="1.0">
    <object pk="1" model="serializers.article">
        <field to="serializers.author" name="author" rel="ManyToOneRel">1</field>
        <field type="CharField" name="headline">Forward references pose no problem</field>
        <field type="DateTimeField" name="pub_date">2006-06-16T15:00:00</field>
        <field to="serializers.category" name="categories" rel="ManyToManyRel">
            <object pk="1"></object>
        </field>
        <field to="serializers.categorymetadata" name="meta_data" rel="ManyToManyRel"></field>
    </object>
    <object pk="1" model="serializers.author">
        <field type="CharField" name="name">Agnes</field>
    </object>
    <object pk="1" model="serializers.category">
        <field type="CharField" name="name">Reference</field></object>
</django-objects>"""


class JsonSerializerTestCase(SerializersTestBase, TestCase):
    serializer_name = "json"
    pkless_str = """[
    {
        "pk": null,
        "model": "serializers.category",
        "fields": {"name": "Reference"}
    }, {
        "model": "serializers.category",
        "fields": {"name": "Non-fiction"}
    }]"""
    mapping_ordering_str = """[
{
  "model": "serializers.article",
  "pk": %(article_pk)s,
  "fields": {
    "author": %(author_pk)s,
    "headline": "Poker has no place on ESPN",
    "pub_date": "2006-06-16T11:00:00",
    "categories": [
      %(first_category_pk)s,
      %(second_category_pk)s
    ],
    "meta_data": []
  }
}
]
"""

    @staticmethod
    def _validate_output(serial_str):
        try:
            json.loads(serial_str)
        except Exception:
            return False
        else:
            return True

    @staticmethod
    def _get_pk_values(serial_str):
        ret_list = []
        serial_list = json.loads(serial_str)
        for obj_dict in serial_list:
            ret_list.append(obj_dict["pk"])
        return ret_list

    @staticmethod
    def _get_field_values(serial_str, field_name):
        ret_list = []
        serial_list = json.loads(serial_str)
        for obj_dict in serial_list:
            if field_name in obj_dict["fields"]:
                ret_list.append(obj_dict["fields"][field_name])
        return ret_list

    def test_indentation_whitespace(self):
        Score.objects.create(score=5.0)
        Score.objects.create(score=6.0)
        qset = Score.objects.all()

        s = serializers.json.Serializer()
        json_data = s.serialize(qset, indent=2)
        for line in json_data.splitlines():
            if re.search(r'.+,\s*$', line):
                self.assertEqual(line, line.rstrip())

    def test_helpful_error_message_invalid_pk(self):
        """
        If there is an invalid primary key, the error message should contain
        the model associated with it.
        """
        test_string = """[{
            "pk": "badpk",
            "model": "serializers.player",
            "fields": {
                "name": "Bob",
                "rank": 1,
                "team": "Team"
            }
        }]"""
        with self.assertRaisesMessage(serializers.base.DeserializationError, "(serializers.player:pk=badpk)"):
            list(serializers.deserialize('json', test_string))

    def test_helpful_error_message_invalid_field(self):
        """
        If there is an invalid field value, the error message should contain
        the model associated with it.
        """
        test_string = """[{
            "pk": "1",
            "model": "serializers.player",
            "fields": {
                "name": "Bob",
                "rank": "invalidint",
                "team": "Team"
            }
        }]"""
        expected = "(serializers.player:pk=1) field_value was 'invalidint'"
        with self.assertRaisesMessage(serializers.base.DeserializationError, expected):
            list(serializers.deserialize('json', test_string))

    def test_helpful_error_message_for_foreign_keys(self):
        """
        Invalid foreign keys with a natural key should throw a helpful error
        message, such as what the failing key is.
        """
        test_string = """[{
            "pk": 1,
            "model": "serializers.category",
            "fields": {
                "name": "Unknown foreign key",
                "meta_data": [
                    "doesnotexist",
                    "metadata"
                ]
            }
        }]"""
        key = ["doesnotexist", "metadata"]
        expected = "(serializers.category:pk=1) field_value was '%r'" % key
        with self.assertRaisesMessage(serializers.base.DeserializationError, expected):
            list(serializers.deserialize('json', test_string))

    def test_helpful_error_message_for_many2many_non_natural(self):
        """
        Invalid many-to-many keys should throw a helpful error message.
        """
        test_string = """[{
            "pk": 1,
            "model": "serializers.article",
            "fields": {
                "author": 1,
                "headline": "Unknown many to many",
                "pub_date": "2014-09-15T10:35:00",
                "categories": [1, "doesnotexist"]
            }
        }, {
            "pk": 1,
            "model": "serializers.author",
            "fields": {
                "name": "Agnes"
            }
        }, {
            "pk": 1,
            "model": "serializers.category",
            "fields": {
                "name": "Reference"
            }
        }]"""
        expected = "(serializers.article:pk=1) field_value was 'doesnotexist'"
        with self.assertRaisesMessage(serializers.base.DeserializationError, expected):
            list(serializers.deserialize('json', test_string))

    def test_helpful_error_message_for_many2many_natural1(self):
        """
        Invalid many-to-many keys should throw a helpful error message.
        This tests the code path where one of a list of natural keys is invalid.
        """
        test_string = """[{
            "pk": 1,
            "model": "serializers.categorymetadata",
            "fields": {
                "kind": "author",
                "name": "meta1",
                "value": "Agnes"
            }
        }, {
            "pk": 1,
            "model": "serializers.article",
            "fields": {
                "author": 1,
                "headline": "Unknown many to many",
                "pub_date": "2014-09-15T10:35:00",
                "meta_data": [
                    ["author", "meta1"],
                    ["doesnotexist", "meta1"],
                    ["author", "meta1"]
                ]
            }
        }, {
            "pk": 1,
            "model": "serializers.author",
            "fields": {
                "name": "Agnes"
            }
        }]"""
        key = ["doesnotexist", "meta1"]
        expected = "(serializers.article:pk=1) field_value was '%r'" % key
        with self.assertRaisesMessage(serializers.base.DeserializationError, expected):
            for obj in serializers.deserialize('json', test_string):
                obj.save()

    def test_helpful_error_message_for_many2many_natural2(self):
        """
        Invalid many-to-many keys should throw a helpful error message. This
        tests the code path where a natural many-to-many key has only a single
        value.
        """
        test_string = """[{
            "pk": 1,
            "model": "serializers.article",
            "fields": {
                "author": 1,
                "headline": "Unknown many to many",
                "pub_date": "2014-09-15T10:35:00",
                "meta_data": [1, "doesnotexist"]
            }
        }, {
            "pk": 1,
            "model": "serializers.categorymetadata",
            "fields": {
                "kind": "author",
                "name": "meta1",
                "value": "Agnes"
            }
        }, {
            "pk": 1,
            "model": "serializers.author",
            "fields": {
                "name": "Agnes"
            }
        }]"""
        expected = "(serializers.article:pk=1) field_value was 'doesnotexist'"
        with self.assertRaisesMessage(serializers.base.DeserializationError, expected):
            for obj in serializers.deserialize('json', test_string, ignore=False):
                obj.save()


class JsonSerializerTransactionTestCase(SerializersTransactionTestBase, TransactionTestCase):
    serializer_name = "json"
    fwd_ref_str = """[
    {
        "pk": 1,
        "model": "serializers.article",
        "fields": {
            "headline": "Forward references pose no problem",
            "pub_date": "2006-06-16T15:00:00",
            "categories": [1],
            "author": 1
        }
    },
    {
        "pk": 1,
        "model": "serializers.category",
        "fields": {
            "name": "Reference"
        }
    },
    {
        "pk": 1,
        "model": "serializers.author",
        "fields": {
            "name": "Agnes"
        }
    }]"""


YAML_IMPORT_ERROR_MESSAGE = r'No module named yaml'


class YamlImportModuleMock(object):
    """Provides a wrapped import_module function to simulate yaml ImportError

    In order to run tests that verify the behavior of the YAML serializer
    when run on a system that has yaml installed (like the django CI server),
    mock import_module, so that it raises an ImportError when the yaml
    serializer is being imported.  The importlib.import_module() call is
    being made in the serializers.register_serializer().

    Refs: #12756
    """
    def __init__(self):
        self._import_module = importlib.import_module

    def import_module(self, module_path):
        if module_path == serializers.BUILTIN_SERIALIZERS['yaml']:
            raise ImportError(YAML_IMPORT_ERROR_MESSAGE)

        return self._import_module(module_path)


class NoYamlSerializerTestCase(SimpleTestCase):
    """Not having pyyaml installed provides a misleading error

    Refs: #12756
    """
    @classmethod
    def setUpClass(cls):
        """Removes imported yaml and stubs importlib.import_module"""
        super(NoYamlSerializerTestCase, cls).setUpClass()

        cls._import_module_mock = YamlImportModuleMock()
        importlib.import_module = cls._import_module_mock.import_module

        # clear out cached serializers to emulate yaml missing
        serializers._serializers = {}

    @classmethod
    def tearDownClass(cls):
        """Puts yaml back if necessary"""
        super(NoYamlSerializerTestCase, cls).tearDownClass()

        importlib.import_module = cls._import_module_mock._import_module

        # clear out cached serializers to clean out BadSerializer instances
        serializers._serializers = {}

    def test_serializer_pyyaml_error_message(self):
        """Using yaml serializer without pyyaml raises ImportError"""
        jane = Author(name="Jane")
        self.assertRaises(ImportError, serializers.serialize, "yaml", [jane])

    def test_deserializer_pyyaml_error_message(self):
        """Using yaml deserializer without pyyaml raises ImportError"""
        self.assertRaises(ImportError, serializers.deserialize, "yaml", "")

    def test_dumpdata_pyyaml_error_message(self):
        """Calling dumpdata produces an error when yaml package missing"""
        with six.assertRaisesRegex(self, management.CommandError, YAML_IMPORT_ERROR_MESSAGE):
            management.call_command('dumpdata', format='yaml')


@unittest.skipUnless(HAS_YAML, "No yaml library detected")
class YamlSerializerTestCase(SerializersTestBase, TestCase):
    serializer_name = "yaml"
    fwd_ref_str = """- fields:
    headline: Forward references pose no problem
    pub_date: 2006-06-16 15:00:00
    categories: [1]
    author: 1
  pk: 1
  model: serializers.article
- fields:
    name: Reference
  pk: 1
  model: serializers.category
- fields:
    name: Agnes
  pk: 1
  model: serializers.author"""

    pkless_str = """- fields:
    name: Reference
  pk: null
  model: serializers.category
- fields:
    name: Non-fiction
  model: serializers.category"""

    mapping_ordering_str = """- model: serializers.article
  pk: %(article_pk)s
  fields:
    author: %(author_pk)s
    headline: Poker has no place on ESPN
    pub_date: 2006-06-16 11:00:00
    categories: [%(first_category_pk)s, %(second_category_pk)s]
    meta_data: []
"""

    @staticmethod
    def _validate_output(serial_str):
        try:
            yaml.safe_load(StringIO(serial_str))
        except Exception:
            return False
        else:
            return True

    @staticmethod
    def _get_pk_values(serial_str):
        ret_list = []
        stream = StringIO(serial_str)
        for obj_dict in yaml.safe_load(stream):
            ret_list.append(obj_dict["pk"])
        return ret_list

    @staticmethod
    def _get_field_values(serial_str, field_name):
        ret_list = []
        stream = StringIO(serial_str)
        for obj_dict in yaml.safe_load(stream):
            if "fields" in obj_dict and field_name in obj_dict["fields"]:
                field_value = obj_dict["fields"][field_name]
                # yaml.safe_load will return non-string objects for some
                # of the fields we are interested in, this ensures that
                # everything comes back as a string
                if isinstance(field_value, six.string_types):
                    ret_list.append(field_value)
                else:
                    ret_list.append(str(field_value))
        return ret_list


@unittest.skipUnless(HAS_YAML, "No yaml library detected")
class YamlSerializerTransactionTestCase(SerializersTransactionTestBase, TransactionTestCase):
    serializer_name = "yaml"
    fwd_ref_str = """- fields:
    headline: Forward references pose no problem
    pub_date: 2006-06-16 15:00:00
    categories: [1]
    author: 1
  pk: 1
  model: serializers.article
- fields:
    name: Reference
  pk: 1
  model: serializers.category
- fields:
    name: Agnes
  pk: 1
  model: serializers.author"""