django-polymorphic for building a custom model - is polymorphic the right tool? #506
Description
I am writing this ticket to get some some feedback about my implementation and whether django-polymorphic is actually the right way to go. I get some massive performance issue in our prototype and when looking at the performance remarks in the docs I feel like my approach might be doomed and I should consider alternatives soon than later.
I wrote an app where (potentially) users can customize the fields of a model where all fields are stored in a polymorphic model.
The aim of the project is to provide users with a model/form builder and not having to specify the fields in the code.
Users can create a form structure with all the fields in the form and other users may create Projects and add their data according to the structure.
I like the polymorphic approach as I can store the data in native format and profit from out of the box widgets and validations.
A simplified version:
class Project(models.Model):
# some global fields here
name = models.CharField()
class ProjectField(PolymorphicModel):
project = models.ForeignKey(Project)
slug = ... # identify the field when searching
class IntegerProjectField(ProjectField):
value = models.IntegerField()
class TextProjectField(ProjectField):
value = models.TextField()
label = models.CharField(...)
...In reality there is a model for ProjectFields and another model for Structure which the user can configure and upon creation of a Project object, all ProjectField instances are created according to the slugs in Structure. But for simplicity I guess the above example should work.
The approach works so far and looks nice on an ER diagram :P
I get into performance and ergonomic issues when filtering for Projects with a particular value. I end up filtering for the concrete type like IntegerProejctField.objects.filter(slug="xyz", value=123) and retrieve the project from there.
Chaining multiple filters together does not work anymore.
I can do the following to keep the view on the Project. (or probably use Q objects)
This is not very convinient, kinda works but turns out to be slow.
Project.objects.filter(
projectfield__integerprojectfield__value=123,
projectfield__integerprojectfield__slug="xyz"
).filter(
projectfield__textprojectfield__value="some text",
projectfield__textprojectfield__slug="abc"
)
The more pressing issue though is when using FormSets.
Users shall be able to edit data in the Project so I need an inline FormSet.
It works as expected but the performance is really bad. (Note that I also use additional models that need to be joined for each ProjectField so that also adds to the issue)
So to get to the point, I am not sure if django-polymorphic is the right solution for the job.
I am not fully convinced anymore like I was at the beginning.
If django-polymorphic will be a dead end for me, are there any suggestions or libraries for building such a form builder solution?