python - Django REST: serializer field that isn't a model field -

i have 2 models (and matching serializers):

class book(models.model):    created = models.datetimefield(auto_now_add=true)    owner = models.foreignkey(myuser)    title = models.charfield(max_length=100, blank=true, default='')    author = models.charfield(max_length=100, blank=true, default='')  class readby(models.model):    created = models.datetimefield(auto_now_add=true)    owner = models.foreignkey(myuser) 

when book has been read it's stored in readby database. when user retrieves books using book model/serializer want field telling me if particular user has read book.

i.e. add field model book (pseudo-code):

has_been_read_by = if_exists_in_readby display 'true' else 'false' 

so need check if record exists in readby database , display true or false if so.

thanks.

the take away in serializer method of book model, have access context provides context['request'].user , obj represents book object

i assume readby has fk book, otherwise it's not clear how link them together

class readby(models.model):    created = models.datetimefield(auto_now_add=true)    owner = models.foreignkey(myuser)    book = models.foreignkey(book) 

let's make bookserializer

class bookserializer(serializers.modelserializer):     class meta:         model = book      has_been_read_by = serializers.serializermethodfield('get_has_been_read_by')      def get_has_been_read_by(self, obj):         user = self.context['request'].user         book = obj          # see if readby object exists         return readby.objects.filter(book=book, owner=user).exists() 

that field contain either true or false, booleans, translated rest format, e.g. json (or can return true , false strings easily)

now use in viewset e.g.

class bookviewset(viewsets.modelviewset):     model = book     serializer_class = bookserializer