custom serializer fields for events, to be used in superevent serialization

gracedb/events/api/fields.py

+from rest_framework import serializers
+from django.contrib.auth import get_user_model
+
+from ..models import Event
+
+UserModel = get_user_model()
+
+import logging
+logger = logging.getLogger(__name__)
+
+class GenericField(serializers.Field):
+    # Field, property, or callable of the object which will be used to
+    # generate the representation of the object.
+    to_repr = None
+    lookup_field = 'id'
+    model = None
+
+    def __init__(self, *args, **kwargs):
+        self.to_repr = kwargs.pop('to_repr', self.to_repr)
+        self.lookup_field = kwargs.pop('lookup_field', self.lookup_field)
+        self.model = kwargs.pop('model', self.model)
+
+        assert self.to_repr is not None, ('Must specify to_repr')
+        assert self.model is not None, ('Must specify model')
+        super(GenericField, self).__init__(*args, **kwargs)
+
+    def to_representation(self, obj):
+        value = getattr(obj, self.to_repr)
+
+        # Handle case where we are given a function instead of
+        # a model field or a property
+        if callable(value):
+            value = value()
+        return value
+
+    def to_internal_value(self, data):
+        model_dict = self.get_model_dict(data)
+        try:
+            return self.model.objects.get(**model_dict)
+        except self.model.DoesNotExist:
+            error_msg = '{model} with {lf}={data} does not exist' \
+                .format(model=self.model.__name__, lf=model_dict.keys()[0],
+                data=model_dict.values()[0])
+            raise serializers.ValidationError(error_msg)
+
+    def get_model_dict(self, data):
+        return {self.lookup_field: data}
+
+
+class EventGraceidField(GenericField, serializers.RelatedField):
+    to_repr = 'graceid'
+    lookup_field = 'id'
+    model = Event
+    queryset = Event.objects.all()
+
+    def get_model_dict(self, data):
+        return {self.lookup_field: data[1:]}