models.py 文件源码

def make_declarations(cls, container_name, event_type, table_name, table_args, unique_parent):
        """
        Declare columns and indexes.

        An event assumes the following:

         -  Each event belongs to (and has a foreign key to) another "container" table.

            Typically, the container table has immutable rows that define the context of an entity
            and events track state changes to rows of this table.

         -  Each event has a well-defined type, derived from an enumeration.

         -  Each event has a well-defined state, consisting of one or more enumerated values.

         -  Each event has an integer version, starting from one.

            Not every event uses versions; those that do will generally have a uniqueness contraint
            on some event types per version of a container row.

         -  Each event has a nullable parent event id where a null value represents the first event
            in a version and subsequent event have a unique parent id to ensure semantic ordering.

         -  Each event has a non-nullable serial clock to ensure total ordering.

        """
        container_id = "{}.id".format(container_name)
        container_id_name = "{}_id".format(container_name)
        parent_id = "{}.id".format(table_name)

        return {
            # columns
            container_id_name: Column(UUIDType, ForeignKey(container_id), nullable=False),
            "event_type": Column(EnumType(event_type), nullable=False),
            "clock": Column(Serial, server_default=FetchedValue(), nullable=False, unique=True),
            "parent_id": Column(UUIDType, ForeignKey(parent_id), nullable=True, unique=unique_parent),
            "state": Column(ARRAY(EnumType(event_type)), nullable=False, default=default_state),
            "version": Column(Integer, default=1, nullable=False),

            # shortcuts
            "container_id": ColumnAlias(container_id_name),
            "container_id_name": container_id_name,

            # indexes and constraints
            "__table_args__": table_args + cls.make_table_args(cls, table_name, container_id_name, event_type),
        }