# Django 4.2.11 documentation

# Source code for django.db.migrations.operations.fields

    from django.db.migrations.utils import field_references
    from django.db.models import NOT_PROVIDED
    from django.utils.functional import cached_property

    from .base import Operation

    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):
            state.add_field(
                app_label,
                self.model_name_lower,
                self.name,
                self.field,
                self.preserve_default,
            )

        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)

        @property
        def migration_name_fragment(self):
            return "%s_%s" % (self.model_name_lower, self.name_lower)

        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):
            state.remove_field(app_label, self.model_name_lower, self.name)

        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)

        @property
        def migration_name_fragment(self):
            return "remove_%s_%s" % (self.model_name_lower, self.name_lower)

        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):
            state.alter_field(
                app_label,
                self.model_name_lower,
                self.name,
                self.field,
                self.preserve_default,
            )

        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)

        @property
        def migration_name_fragment(self):
            return "alter_%s_%s" % (self.model_name_lower, self.name_lower)

        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)
                and self.field.db_column is None
            ):
                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):
            state.rename_field(
                app_label, self.model_name_lower, self.old_name, self.new_name
            )

        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,
            )

        @property
        def migration_name_fragment(self):
            return "rename_%s_%s_%s" % (
                self.old_name_lower,
                self.model_name_lower,
                self.new_name_lower,
            )

        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.old_name and self.new_name.
            return super(FieldOperation, self).reduce(operation, app_label) or not (
                operation.references_field(self.model_name, self.old_name, app_label)
                or operation.references_field(self.model_name, self.new_name, app_label)
            )