simplify page index serialisation

backend/addcorpus/models.py

@@ -473,6 +473,13 @@ class PageType(models.TextChoices):
         help_text='markdown contents of the documentation'
     )
 
+    @property
+    def page_index(self):
+        '''Numerical index to determine the order in which pages should be displayed.
+        Based on the order in which `PageType` choices are declared.'''
+        indexed_values = enumerate(__class__.PageType.values)
+        return next((i for (i, value) in indexed_values if value == self.type), None)
+
     def __str__(self):
         return f'{self.corpus_configuration.corpus.name} - {self.type}'
 

backend/addcorpus/serializers.py

@@ -131,29 +131,9 @@ def to_representation(self, value):
         return render_documentation_context(content)
 
 
-class ChoiceOrderSerializer(serializers.ChoiceField):
-    '''
-    Variant on the ChoiceField that serialises to the index in the choices array.
-    '''
-    def __init__(self, choices, **kwargs):
-        super().__init__(choices=choices, **kwargs)
-        self.index = {value: i for i, (value, label) in enumerate(choices)}
-
-    def to_internal_value(self, data):
-        return self.choices[data]
-
-    def to_representation(self, value):
-        key = super().to_representation(value)
-        return self.index[key]
-
-
 class CorpusDocumentationPageSerializer(serializers.ModelSerializer):
     type = PrettyChoiceField(choices = CorpusDocumentationPage.PageType.choices)
-    index = ChoiceOrderSerializer(
-        read_only=True,
-        source='type',
-        choices=CorpusDocumentationPage.PageType.choices,
-    )
+    index = serializers.IntegerField(source='page_index', read_only=True)
     content = DocumentationTemplateField(read_only=True)
     content_template = serializers.CharField(source='content')
     corpus = serializers.SlugRelatedField(

backend/addcorpus/tests/test_models.py

@@ -1,4 +1,4 @@
-from addcorpus.models import Corpus
+from addcorpus.models import Corpus, CorpusDocumentationPage
 
 def test_corpus_model(db):
     corpus = Corpus(name = 'test_corpus')
@@ -9,3 +9,12 @@ def test_corpus_model(db):
     corpus.delete()
 
     assert not Corpus.objects.filter(name = corpus)
+
+def test_corpus_documentation_page_model(db, basic_mock_corpus):
+    corpus = Corpus.objects.get(name=basic_mock_corpus)
+    page = CorpusDocumentationPage(
+        corpus_configuration=corpus.configuration,
+        type=CorpusDocumentationPage.PageType.LICENSE,
+        content='Do whatever you want.',
+    )
+    assert page.page_index == 2