Class Operation
Base class for migration operations.
Declaration
class Operation
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It's responsible for both mutating the in-memory model state
(see db/migrations/state.py) to represent what it performs, as well
as actually performing it against a live database.
Note that some operations won't modify memory state at all (e.g. data
copying operations), and some will need their modifications to be
optionally specified by the user (e.g. custom Python code snippets)
Due to the way this class deals with deconstruction, it should be
considered immutable.
Methods
▷ def __new__(cls, *args, **kwargs) ▶ def allow_migrate_model(self, connection_alias, model) Return whether or not a model may be migrated.
This is a thin wrapper around router.allow_migrate_model() that
preemptively rejects any proxy, swapped out, or unmanaged model.
▶ def database_backwards(self, app_label, schema_editor, from_state, to_state) Perform the mutation on the database schema in the reverse direction - e.g. if this were CreateModel, it would in fact drop the model's table.
Overrides
This method is overriden in:
▶ def database_forwards(self, app_label, schema_editor, from_state, to_state) Perform the mutation on the database schema in the normal (forwards) direction.
Overrides
This method is overriden in:
▶ def deconstruct(self) Return a 3-tuple of class import path (or just name if it lives under django.db.migrations), positional arguments, and keyword arguments.
Overrides
This method is overriden in:
▶ def describe(self) Output a brief summary of what the action does.
Overrides
This method is overriden in:
▶ def migration_name_fragment(self) @property A filename part suitable for automatically naming a migration containing this operation, or None if not applicable.
@property
def migration_name_fragment(self)
Overrides
This method is overriden in:
▶ def reduce(self, operation, app_label) Return either a list of operations the actual operation should be replaced with or a boolean that indicates whether or not the specified operation can be optimized across.
Overrides
This method is overriden in:
▶ def references_field(self, model_name, name, app_label) Return True if there is a chance this operation references the given field name, with an app label for accuracy.
Used for optimization. If in doubt, return True.
Overrides
This method is overriden in:
▶ def references_model(self, name, app_label) Return True if there is a chance this operation references the given model name (as a string), with an app label for accuracy.
Used for optimization. If in doubt, return True;
returning a false positive will merely make the optimizer a little
less efficient, while returning a false negative may result in an
unusable optimized migration.
Overrides
This method is overriden in:
▶ def state_forwards(self, app_label, state) Take the state from the previous migration, and mutate it so that it matches what this migration would perform.
Overrides
This method is overriden in:
Subclasses
Reexports