92 lines
3.3 KiB
Python
92 lines
3.3 KiB
Python
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from django.core.exceptions import ImproperlyConfigured
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from django.db import models
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from wagtail.coreutils import resolve_model_string
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class ObjectTypeRegistry:
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"""
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Implements a lookup table for mapping objects to values according to the object type.
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The most specific type according to the object's inheritance chain is selected.
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"""
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def __init__(self):
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# values in this dict will be returned if the field type exactly matches an item here
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self.values_by_exact_class = {}
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# values in this dict will be returned if any class in the field's inheritance chain
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# matches, preferring more specific subclasses
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self.values_by_class = {}
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def register(self, cls, value=None, exact_class=False):
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if exact_class:
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self.values_by_exact_class[cls] = value
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else:
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self.values_by_class[cls] = value
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def get_by_type(self, cls):
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try:
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return self.values_by_exact_class[cls]
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except KeyError:
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for ancestor in cls.mro():
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try:
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return self.values_by_class[ancestor]
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except KeyError:
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pass
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def get(self, obj):
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value = self.get_by_type(obj.__class__)
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if callable(value) and not isinstance(value, type):
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value = value(obj)
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return value
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class ModelFieldRegistry(ObjectTypeRegistry):
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"""
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Handles the recurring pattern where we need to register different values for different
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model field types, and retrieve the one that most closely matches a given model field,
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according to its type (taking inheritance into account), and in the case of foreign keys,
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the type of the related model (again, taking inheritance into account).
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For example, this is used by wagtail.admin.forms.models when constructing model forms:
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we use such a registry to retrieve the appropriate dict of arguments to pass to the
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form field constructor. A lookup for a models.TextField will return a dict specifying a
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text area widget, and a lookup for a foreign key to Image will return a dict specifying
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an image chooser widget.
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"""
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def __init__(self):
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super().__init__()
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self.values_by_class[models.ForeignKey] = self.foreign_key_lookup
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# values in this dict will be returned if the field is a foreign key to a related
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# model in here, matching most specific subclass first
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self.values_by_fk_related_model = {}
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def register(self, field_class, to=None, value=None, exact_class=False):
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if to:
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if field_class == models.ForeignKey:
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self.values_by_fk_related_model[resolve_model_string(to)] = value
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else:
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raise ImproperlyConfigured(
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"The 'to' argument on ModelFieldRegistry.register is only valid for ForeignKey fields"
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)
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else:
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super().register(field_class, value=value, exact_class=exact_class)
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def foreign_key_lookup(self, field):
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value = None
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target_model = field.remote_field.model
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for model in target_model.mro():
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if model in self.values_by_fk_related_model:
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value = self.values_by_fk_related_model[model]
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break
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if callable(value) and not isinstance(value, type):
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value = value(field)
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return value
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