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Lib/site-packages/django/db/migrations/operations/fields.py

@@ -0,0 +1,379 @@
+from django.core.exceptions import FieldDoesNotExist
+from django.db.models import NOT_PROVIDED
+from django.utils.functional import cached_property
+
+from .base import Operation
+from .utils import field_is_referenced, field_references, get_references
+
+
+class FieldOperation(Operation):
+    def __init__(self, model_name, name, field=None):
+        self.model_name = model_name
+        self.name = name
+        self.field = field
+
+    @cached_property
+    def model_name_lower(self):
+        return self.model_name.lower()
+
+    @cached_property
+    def name_lower(self):
+        return self.name.lower()
+
+    def is_same_model_operation(self, operation):
+        return self.model_name_lower == operation.model_name_lower
+
+    def is_same_field_operation(self, operation):
+        return self.is_same_model_operation(operation) and self.name_lower == operation.name_lower
+
+    def references_model(self, name, app_label):
+        name_lower = name.lower()
+        if name_lower == self.model_name_lower:
+            return True
+        if self.field:
+            return bool(field_references(
+                (app_label, self.model_name_lower), self.field, (app_label, name_lower)
+            ))
+        return False
+
+    def references_field(self, model_name, name, app_label):
+        model_name_lower = model_name.lower()
+        # Check if this operation locally references the field.
+        if model_name_lower == self.model_name_lower:
+            if name == self.name:
+                return True
+            elif self.field and hasattr(self.field, 'from_fields') and name in self.field.from_fields:
+                return True
+        # Check if this operation remotely references the field.
+        if self.field is None:
+            return False
+        return bool(field_references(
+            (app_label, self.model_name_lower),
+            self.field,
+            (app_label, model_name_lower),
+            name,
+        ))
+
+    def reduce(self, operation, app_label):
+        return (
+            super().reduce(operation, app_label) or
+            not operation.references_field(self.model_name, self.name, app_label)
+        )
+
+
+class AddField(FieldOperation):
+    """Add a field to a model."""
+
+    def __init__(self, model_name, name, field, preserve_default=True):
+        self.preserve_default = preserve_default
+        super().__init__(model_name, name, field)
+
+    def deconstruct(self):
+        kwargs = {
+            'model_name': self.model_name,
+            'name': self.name,
+            'field': self.field,
+        }
+        if self.preserve_default is not True:
+            kwargs['preserve_default'] = self.preserve_default
+        return (
+            self.__class__.__name__,
+            [],
+            kwargs
+        )
+
+    def state_forwards(self, app_label, state):
+        # If preserve default is off, don't use the default for future state
+        if not self.preserve_default:
+            field = self.field.clone()
+            field.default = NOT_PROVIDED
+        else:
+            field = self.field
+        state.models[app_label, self.model_name_lower].fields[self.name] = field
+        # Delay rendering of relationships if it's not a relational field
+        delay = not field.is_relation
+        state.reload_model(app_label, self.model_name_lower, delay=delay)
+
+    def database_forwards(self, app_label, schema_editor, from_state, to_state):
+        to_model = to_state.apps.get_model(app_label, self.model_name)
+        if self.allow_migrate_model(schema_editor.connection.alias, to_model):
+            from_model = from_state.apps.get_model(app_label, self.model_name)
+            field = to_model._meta.get_field(self.name)
+            if not self.preserve_default:
+                field.default = self.field.default
+            schema_editor.add_field(
+                from_model,
+                field,
+            )
+            if not self.preserve_default:
+                field.default = NOT_PROVIDED
+
+    def database_backwards(self, app_label, schema_editor, from_state, to_state):
+        from_model = from_state.apps.get_model(app_label, self.model_name)
+        if self.allow_migrate_model(schema_editor.connection.alias, from_model):
+            schema_editor.remove_field(from_model, from_model._meta.get_field(self.name))
+
+    def describe(self):
+        return "Add field %s to %s" % (self.name, self.model_name)
+
+    def reduce(self, operation, app_label):
+        if isinstance(operation, FieldOperation) and self.is_same_field_operation(operation):
+            if isinstance(operation, AlterField):
+                return [
+                    AddField(
+                        model_name=self.model_name,
+                        name=operation.name,
+                        field=operation.field,
+                    ),
+                ]
+            elif isinstance(operation, RemoveField):
+                return []
+            elif isinstance(operation, RenameField):
+                return [
+                    AddField(
+                        model_name=self.model_name,
+                        name=operation.new_name,
+                        field=self.field,
+                    ),
+                ]
+        return super().reduce(operation, app_label)
+
+
+class RemoveField(FieldOperation):
+    """Remove a field from a model."""
+
+    def deconstruct(self):
+        kwargs = {
+            'model_name': self.model_name,
+            'name': self.name,
+        }
+        return (
+            self.__class__.__name__,
+            [],
+            kwargs
+        )
+
+    def state_forwards(self, app_label, state):
+        model_state = state.models[app_label, self.model_name_lower]
+        old_field = model_state.fields.pop(self.name)
+        # Delay rendering of relationships if it's not a relational field
+        delay = not old_field.is_relation
+        state.reload_model(app_label, self.model_name_lower, delay=delay)
+
+    def database_forwards(self, app_label, schema_editor, from_state, to_state):
+        from_model = from_state.apps.get_model(app_label, self.model_name)
+        if self.allow_migrate_model(schema_editor.connection.alias, from_model):
+            schema_editor.remove_field(from_model, from_model._meta.get_field(self.name))
+
+    def database_backwards(self, app_label, schema_editor, from_state, to_state):
+        to_model = to_state.apps.get_model(app_label, self.model_name)
+        if self.allow_migrate_model(schema_editor.connection.alias, to_model):
+            from_model = from_state.apps.get_model(app_label, self.model_name)
+            schema_editor.add_field(from_model, to_model._meta.get_field(self.name))
+
+    def describe(self):
+        return "Remove field %s from %s" % (self.name, self.model_name)
+
+    def reduce(self, operation, app_label):
+        from .models import DeleteModel
+        if isinstance(operation, DeleteModel) and operation.name_lower == self.model_name_lower:
+            return [operation]
+        return super().reduce(operation, app_label)
+
+
+class AlterField(FieldOperation):
+    """
+    Alter a field's database column (e.g. null, max_length) to the provided
+    new field.
+    """
+
+    def __init__(self, model_name, name, field, preserve_default=True):
+        self.preserve_default = preserve_default
+        super().__init__(model_name, name, field)
+
+    def deconstruct(self):
+        kwargs = {
+            'model_name': self.model_name,
+            'name': self.name,
+            'field': self.field,
+        }
+        if self.preserve_default is not True:
+            kwargs['preserve_default'] = self.preserve_default
+        return (
+            self.__class__.__name__,
+            [],
+            kwargs
+        )
+
+    def state_forwards(self, app_label, state):
+        if not self.preserve_default:
+            field = self.field.clone()
+            field.default = NOT_PROVIDED
+        else:
+            field = self.field
+        model_state = state.models[app_label, self.model_name_lower]
+        model_state.fields[self.name] = field
+        # TODO: investigate if old relational fields must be reloaded or if it's
+        # sufficient if the new field is (#27737).
+        # Delay rendering of relationships if it's not a relational field and
+        # not referenced by a foreign key.
+        delay = (
+            not field.is_relation and
+            not field_is_referenced(
+                state, (app_label, self.model_name_lower), (self.name, field),
+            )
+        )
+        state.reload_model(app_label, self.model_name_lower, delay=delay)
+
+    def database_forwards(self, app_label, schema_editor, from_state, to_state):
+        to_model = to_state.apps.get_model(app_label, self.model_name)
+        if self.allow_migrate_model(schema_editor.connection.alias, to_model):
+            from_model = from_state.apps.get_model(app_label, self.model_name)
+            from_field = from_model._meta.get_field(self.name)
+            to_field = to_model._meta.get_field(self.name)
+            if not self.preserve_default:
+                to_field.default = self.field.default
+            schema_editor.alter_field(from_model, from_field, to_field)
+            if not self.preserve_default:
+                to_field.default = NOT_PROVIDED
+
+    def database_backwards(self, app_label, schema_editor, from_state, to_state):
+        self.database_forwards(app_label, schema_editor, from_state, to_state)
+
+    def describe(self):
+        return "Alter field %s on %s" % (self.name, self.model_name)
+
+    def reduce(self, operation, app_label):
+        if isinstance(operation, RemoveField) and self.is_same_field_operation(operation):
+            return [operation]
+        elif isinstance(operation, RenameField) and self.is_same_field_operation(operation):
+            return [
+                operation,
+                AlterField(
+                    model_name=self.model_name,
+                    name=operation.new_name,
+                    field=self.field,
+                ),
+            ]
+        return super().reduce(operation, app_label)
+
+
+class RenameField(FieldOperation):
+    """Rename a field on the model. Might affect db_column too."""
+
+    def __init__(self, model_name, old_name, new_name):
+        self.old_name = old_name
+        self.new_name = new_name
+        super().__init__(model_name, old_name)
+
+    @cached_property
+    def old_name_lower(self):
+        return self.old_name.lower()
+
+    @cached_property
+    def new_name_lower(self):
+        return self.new_name.lower()
+
+    def deconstruct(self):
+        kwargs = {
+            'model_name': self.model_name,
+            'old_name': self.old_name,
+            'new_name': self.new_name,
+        }
+        return (
+            self.__class__.__name__,
+            [],
+            kwargs
+        )
+
+    def state_forwards(self, app_label, state):
+        model_state = state.models[app_label, self.model_name_lower]
+        # Rename the field
+        fields = model_state.fields
+        try:
+            found = fields.pop(self.old_name)
+        except KeyError:
+            raise FieldDoesNotExist(
+                "%s.%s has no field named '%s'" % (app_label, self.model_name, self.old_name)
+            )
+        fields[self.new_name] = found
+        for field in fields.values():
+            # Fix from_fields to refer to the new field.
+            from_fields = getattr(field, 'from_fields', None)
+            if from_fields:
+                field.from_fields = tuple([
+                    self.new_name if from_field_name == self.old_name else from_field_name
+                    for from_field_name in from_fields
+                ])
+        # Fix index/unique_together to refer to the new field
+        options = model_state.options
+        for option in ('index_together', 'unique_together'):
+            if option in options:
+                options[option] = [
+                    [self.new_name if n == self.old_name else n for n in together]
+                    for together in options[option]
+                ]
+        # Fix to_fields to refer to the new field.
+        delay = True
+        references = get_references(
+            state, (app_label, self.model_name_lower), (self.old_name, found),
+        )
+        for *_, field, reference in references:
+            delay = False
+            if reference.to:
+                remote_field, to_fields = reference.to
+                if getattr(remote_field, 'field_name', None) == self.old_name:
+                    remote_field.field_name = self.new_name
+                if to_fields:
+                    field.to_fields = tuple([
+                        self.new_name if to_field_name == self.old_name else to_field_name
+                        for to_field_name in to_fields
+                    ])
+        state.reload_model(app_label, self.model_name_lower, delay=delay)
+
+    def database_forwards(self, app_label, schema_editor, from_state, to_state):
+        to_model = to_state.apps.get_model(app_label, self.model_name)
+        if self.allow_migrate_model(schema_editor.connection.alias, to_model):
+            from_model = from_state.apps.get_model(app_label, self.model_name)
+            schema_editor.alter_field(
+                from_model,
+                from_model._meta.get_field(self.old_name),
+                to_model._meta.get_field(self.new_name),
+            )
+
+    def database_backwards(self, app_label, schema_editor, from_state, to_state):
+        to_model = to_state.apps.get_model(app_label, self.model_name)
+        if self.allow_migrate_model(schema_editor.connection.alias, to_model):
+            from_model = from_state.apps.get_model(app_label, self.model_name)
+            schema_editor.alter_field(
+                from_model,
+                from_model._meta.get_field(self.new_name),
+                to_model._meta.get_field(self.old_name),
+            )
+
+    def describe(self):
+        return "Rename field %s on %s to %s" % (self.old_name, self.model_name, self.new_name)
+
+    def references_field(self, model_name, name, app_label):
+        return self.references_model(model_name, app_label) and (
+            name.lower() == self.old_name_lower or
+            name.lower() == self.new_name_lower
+        )
+
+    def reduce(self, operation, app_label):
+        if (isinstance(operation, RenameField) and
+                self.is_same_model_operation(operation) and
+                self.new_name_lower == operation.old_name_lower):
+            return [
+                RenameField(
+                    self.model_name,
+                    self.old_name,
+                    operation.new_name,
+                ),
+            ]
+        # Skip `FieldOperation.reduce` as we want to run `references_field`
+        # against self.new_name.
+        return (
+            super(FieldOperation, self).reduce(operation, app_label) or
+            not operation.references_field(self.model_name, self.new_name, app_label)
+        )