models: add a WeekRankField model field to store a choice of weekrank between 0 and 5

This field maps list of small integers to their encoding as a binary
number. It allows efficient lookup for "in" filters.

calebasse/models.py

@@ -1,7 +1,11 @@
 # -*- coding: utf-8 -*-
 
 from django.db import models
+from django.db.models import fields
+from django import forms
 from django.contrib.localflavor.fr.forms import FRPhoneNumberField, FRZipCodeField
+from django.utils.text import capfirst
+
 
 class BaseModelMixin(object):
     def __repr__(self):
@@ -29,16 +33,73 @@ class ZipCodeField(models.CharField):
         default.update(kwargs)
         return super(ZipCodeField, self).formfield(**kwargs)
 
-
-
-class WeekdayField(models.CharField):
-    WEEKDAYS = (u'lundi', u'mardi', u'mercredi', u'jeudi', u'vendredi')
-
-    WEEKDAYS_CHOICE = ((None, u'Aucun'),) \
-            + tuple(zip(WEEKDAYS, map(unicode.title, WEEKDAYS)))
+class WeekRankField(models.PositiveIntegerField):
+    '''Map a list of integers to its encoding as a binary number'''
+    __metaclass__ = models.SubfieldBase
 
     def __init__(self, **kwargs):
-        kwargs['max_length'] = 16
-        kwargs['choices'] = WeekdayField.WEEKDAYS_CHOICE
-        super(WeekdayField, self).__init__(**kwargs)
+        kwargs['blank'] = True
+        kwargs['null'] = True
+        super(WeekRankField, self).__init__(**kwargs)
 
+    def to_python(self, value):
+        if isinstance(value, list):
+            if value:
+                try:
+                    value = map(int, value)
+                except ValueError:
+                    raise forms.ValidationError('value must be a sequence of value coercible to integers')
+                if any((i < 0 or i > 4 for i in value)):
+                    raise forms.ValidationError('value must be a list of integers between 0 and 4')
+                return map(int, set(value))
+            else:
+                return None
+        value = super(WeekRankField, self).to_python(value)
+        if value is None:
+            return None
+        try:
+            value = int(value)
+        except ValueError:
+            raise forms.ValidationError('value must be convertible to an integer')
+        if value < 0 or value >= 64:
+            raise forms.ValidationError('value must be between 0 and 64')
+        return tuple((i for i in range(0, 5) if (1 << i) & value))
+
+
+    def clean(self, value, model_instance):
+        """
+        Convert the value's type and run validation. Validation errors
+        from to_python and validate are propagated. The correct value is
+        returned if no error is raised.
+        """
+        value = self.to_python(value)
+        [self.validate(v, model_instance) for v in value]
+        self.run_validators(value)
+        return value
+
+
+    def get_prep_lookup(self, lookup_type, value):
+        if lookup_type in ('exact', 'in'):
+            s = set(((1 << v) | i for v in value for i in range(0, 64)))
+            return s
+        elif lookup_type == 'range':
+            value = sorted(value)
+            return set(((1 << v) | i for v in range(value[0], value[1]) for i in range(0, 64)))
+        else:
+            return fields.Field.get_prep_lookup(self, lookup_type, value)
+
+
+    def get_prep_value(self, value):
+        if value:
+            x = sum((1 << int(i) for i in value))
+            return x
+        else:
+            return None
+
+    def formfield(self, **kwargs):
+        defaults = {'required': not self.blank, 'label': capfirst(self.verbose_name), 
+                    'help_text': self.help_text, 'choices': self.get_choices(include_blank=False)}
+        if self.has_default():
+            defaults['initial'] = self.get_default()
+        defaults.update(kwargs)
+        return forms.MultipleChoiceField(**defaults)