How to store arbitrary name/value key pairs in a Django model

djangodjango-models

I have a fixed data model that has a lot of data fields.

class Widget(Models.model):
    widget_owner = models.ForeignKey(auth.User)
    val1 = models.CharField()
    val2 = models.CharField()
    ...
    val568 = ...

I want to cram even more data into this Widget by letting my users specify custom data fields. What's a sane way to do this? Is storing name/value pairs where the user can specify additional "Widget fields" a good idea? My pseudo thoughts are below:

data_types = ('free_text', 'date', 'integer', 'price')
class CustomWidgetField(models.Model)
  owner = ForeignKey(auth.User)
  field_title = models.CharField(auth.User)
  field_value_type = models.CharField(choices = data_types)

class CustomWidgetValue(models.Model)
  field_type = ForeignKey(CustomWidgetField)
  widget = ForeignKey(Widget)
  value = models.TextField()

So I want to let each user build a new type of data field that will apply to all of their widgets and then specify values for each custom field in each widget. I will probably have to do filtering/searching on these custom fields just as I would on a native field (which I assume will be much slower than operating on native fields.) But the scale is to have a few dozen custom fields per Widget and each User will only have a few thousand Widgets in their inventory. I can also probably batch most of the searching/filtering on the custom fields into a backend script (maybe.)

Best Answer

Consider representing all custom properties with serialized dict. I used this in a recent project and it worked really well.

 class Widget(models.Model):
      owner = models.ForeignKey(auth.User)
      props = models.TextField(blank=True) # serialized custom data

      @property
      def props_dict(self):
          return simplejson.loads(self.props)

 class UserProfile(models.Model)
      user = models.ForeignKey(auth.User)
      widget_fields = models.TextField(blank=True) # serialized schema declaration
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