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POSQLAlchemy - Mixin vs MetaClass modification
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  1. POSQLAlchemy - Mixin vs MetaClass modification
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    copied!<p>So say, for example I have two classes:</p> <pre><code>Base = declarative_base() class Vendor(Base): __tablename__ = "vendor" id = Column(Integer, primary_key=True) name = Column(String(45)) def __init__(self, name): self.name = name def __repr__(self): return "&lt;Vendor id=%d&gt;" % self.id class Site(Base): __tablename__ = "site" id = Column(Integer, primary_key=True) vendor_id = Column(Integer, ForeignKey('vendor.id')) vendor = relation(Vendor) def __init__(self, name, code, location): self.name = name def __repr__(self): return "&lt;Site id=%d&gt;" % self.id class SQLSchema: def __init__(self): self.engine = create_engine('...', echo=False) self.metadata = Base.metadata self.session = sessionmaker(bind=self.engine)() self.create() def create(self): self.metadata.create_all(self.engine) </code></pre> <p>I've simplified the class structure, now, using these classes, I can use:</p> <pre><code>sql = sqlschema.SQLSchema() </code></pre> <p>So, at times, I want easy access to a Vendor, which means I can use:</p> <pre><code>v = sql.session.query(self).filter_by(name='test').one() </code></pre> <p>I'd prefer to simplify the access by using akin to (currently my best effort):</p> <pre><code>Vendor.get(sql.session, name='A-01') </code></pre> <p>It struck me, that the <code>get</code> function is pretty generic that I'd want across all my classes that inherit from Base and I looked into the best way of doing this. There are two ways I can think of:</p> <ul> <li>a Mix-in class</li> <li>Modifying the metaclass supplied to declarative_base</li> </ul> <p>Example of the metaclass modification</p> <pre><code>class MyDeclarativeMeta(DeclarativeMeta): def get(self, session, **filterargs): session.query(self).filter_by(**filterargs).one() ## ... Base = declarative_base(metaclass=MyDeclarativeMeta) </code></pre> <p>I'd like to create something with the least surprise possible. What are people's opinions on the options I've presented and is there a better way altogether?</p>
 

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