62 lines
2.1 KiB
Python
62 lines
2.1 KiB
Python
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class KeepUnselectableModelFormMixin:
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"""
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Keep unselectable items of queryset-based fields.
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Mixin for 'ModelForm'.
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Attribute
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keep_unselectable_fields (list of field names)
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This adding is performed in 'save' method. Specifically, if 'commit' arg
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is False, it's done in 'save_m2m' method.
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These fields must have a 'queryset' attribute (the selectable items), like
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'ModelMultipleChoiceField' (default field for ManyToMany model fields).
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"""
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keep_unselectable_fields = []
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def get_unselectable(self, field_name):
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"""
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Returns 'field_name' model field items of instance which can't be
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selected with the corresponding form field.
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Should be used before 'form.save' call, or 'form.save_m2m' call if
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'commit=False' was passed as argument to 'form.save'.
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"""
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if self.instance.pk:
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previous = getattr(self.instance, field_name).all()
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selectable = self.fields[field_name].queryset
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return previous.exclude(pk__in=[o.pk for o in selectable])
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else:
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# Instance is being created, there is no previous item.
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return []
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def save(self, commit=True):
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# Use 'commit=False' to get the 'save_m2m' method.
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instance = super().save(commit=False)
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_save_m2m = self.save_m2m
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def save_m2m():
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# Get the unselectable items.
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# Force evaluate because those items are going to change.
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unselectable_f = {
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f_name: list(self.get_unselectable(f_name))
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for f_name in self.keep_unselectable_fields
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}
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# Default 'save_m2m' use 'set' method of m2m relationships with
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# fields' cleaned data.
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_save_m2m()
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# Add the unselectable elements.
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for f_name, unselectable in unselectable_f.items():
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getattr(instance, f_name).add(*unselectable)
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# Implement the default behavior of 'save' method, with our own
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# 'save_m2m'.
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if commit:
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instance.save()
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save_m2m()
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else:
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self.save_m2m = save_m2m
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return instance
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