Hi,
I'm currently learning the how to set up a basic Entity System with
sqlalchemy. The entity system requirements are described within this link:
http://t-machine.org/index.php/2009/10/26/entity-systems-are-the-future-of-mmos-part-5/
Basically, an Entity that lives with the world is defined by the Components
that are attached to it. The nature of the Entity is described by the
combinations of Components attached to the entity. An Entity can change
it's nature by removing or adding a Component to the entity. Every
Component is backed by a table with it's associated data. The Components
are indexed within the 'components_dir' table. As you can see by the schema
below, each Entity can be mapped differently to different Components based
of EntityComponentMap and this can change anytime with the state of the
object.
In order to grab an Entity's component data, I'll retrieve the Component's
tablename via ComponentsDirectory. I'll then manually retrieve the data row
with component_id from it's individual component table.
I'm sorry, I'm kinda really new to sqlalchemy or database based
programming, but is there anyway for sqlalchemy to dynamically directly map
or join the entity to the individual final component data tables?
I've setup the following tables:
class Entity(Base):
__tablename__ = 'entities'
id = Column(Integer, primary_key=True)
name = Column(String)
class ComponentsDirectory(Base):
__tablename__ = 'components_dir'
id = Column(Integer, primary_key=True)
name = Column(String, nullable=False, unique=True)
cls_name = Column(String, nullable=False, unique=True)
table_name = Column(String, nullable=False, unique=True)
class EntityComponentMap(Base):
__tablename__ = 'entity_component_map'
id = Column(Integer, primary_key=True)
entity_id = Column(Integer, ForeignKey('entities.id'))
component_type_id = Column(Integer, ForeignKey(components_dir.id))
component_id = Column(Integer)
entity = relationship('Entity',
backref=backref('component_types_assoc'))
component_type = relationship('ComponentsDirectory',
backref=backref('entities_assoc'))
class ComponentA(Base):
__tablename__ = 'component_b'
id = Column(Integer, primary_key=True)
data_field1 = Column(Integer)
class ComponentB(Base):
__tablename__ = 'component_b'
id = Column(Integer, primary_key=True)
data_field1 = Column(Integer)
data_field2 = Column(String)
class ComponentC(Base):
__tablename__ = 'component_c'
id = Column(Integer, primary_key=True)
data_field1 = Column(Integer)
data_field2 = Column(String)
data_field3 = Column(Boolean)
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