mirror of
https://github.com/sqlalchemy/sqlalchemy.git
synced 2026-05-28 03:26:01 -04:00
Mike Bayer
96 lines
3.2 KiB
Python
96 lines
3.2 KiB
Python
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from sqlalchemy import (MetaData, Table, Column, Integer, String, ForeignKey,
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create_engine)
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from sqlalchemy.orm import (mapper, relationship, sessionmaker)
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meta = MetaData()
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org_table = Table('organizations', meta,
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Column('org_id', Integer, primary_key=True),
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Column('org_name', String(50), nullable=False, key='name'),
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mysql_engine='InnoDB')
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member_table = Table('members', meta,
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Column('member_id', Integer, primary_key=True),
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Column('member_name', String(50), nullable=False, key='name'),
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Column('org_id', Integer,
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ForeignKey('organizations.org_id', ondelete="CASCADE")),
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mysql_engine='InnoDB')
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class Organization(object):
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def __init__(self, name):
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self.name = name
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class Member(object):
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def __init__(self, name):
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self.name = name
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mapper(Organization, org_table, properties = {
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'members' : relationship(Member,
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# Organization.members will be a Query object - no loading
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# of the entire collection occurs unless requested
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lazy="dynamic",
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# Member objects "belong" to their parent, are deleted when
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# removed from the collection
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cascade="all, delete-orphan",
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# "delete, delete-orphan" cascade does not load in objects on delete,
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# allows ON DELETE CASCADE to handle it.
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# this only works with a database that supports ON DELETE CASCADE -
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# *not* sqlite or MySQL with MyISAM
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passive_deletes=True,
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)
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})
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mapper(Member, member_table)
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if __name__ == '__main__':
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engine = create_engine("postgresql://scott:tiger@localhost/test", echo=True)
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meta.create_all(engine)
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# expire_on_commit=False means the session contents
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# will not get invalidated after commit.
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sess = sessionmaker(engine, expire_on_commit=False)()
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# create org with some members
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org = Organization('org one')
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org.members.append(Member('member one'))
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org.members.append(Member('member two'))
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org.members.append(Member('member three'))
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sess.add(org)
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print("-------------------------\nflush one - save org + 3 members\n")
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sess.commit()
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# the 'members' collection is a Query. it issues
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# SQL as needed to load subsets of the collection.
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print("-------------------------\nload subset of members\n")
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members = org.members.filter(member_table.c.name.like('%member t%')).all()
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print(members)
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# new Members can be appended without any
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# SQL being emitted to load the full collection
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org.members.append(Member('member four'))
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org.members.append(Member('member five'))
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org.members.append(Member('member six'))
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print("-------------------------\nflush two - save 3 more members\n")
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sess.commit()
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# delete the object. Using ON DELETE CASCADE
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# SQL is only emitted for the head row - the Member rows
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# disappear automatically without the need for additional SQL.
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sess.delete(org)
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print("-------------------------\nflush three - delete org, delete members in one statement\n")
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sess.commit()
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print("-------------------------\nno Member rows should remain:\n")
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print(sess.query(Member).count())
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sess.close()
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print("------------------------\ndone. dropping tables.")
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meta.drop_all(engine) |