mirror of
https://github.com/sqlalchemy/sqlalchemy.git
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Mike Bayer
5df1759e15
- inline default execution occurs for *all* non-PK columns unconditionally - preexecute only for non-executemany PK cols on PG, Oracle, etc. - new default docs
92 lines
3.3 KiB
Python
92 lines
3.3 KiB
Python
"""illlustrates techniques for dealing with very large collections.
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Also see the docs regarding the new "dynamic" relation option, which
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presents a more refined version of some of these patterns.
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"""
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from sqlalchemy import *
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from sqlalchemy.orm import *
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meta = MetaData('sqlite://')
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meta.bind.echo = True
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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, ForeignKey('organizations.org_id')),
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mysql_engine='InnoDB')
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meta.create_all()
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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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member_query = property(lambda self:object_session(self).query(Member).with_parent(self),
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doc="""locate a subset of the members associated with this Organization""")
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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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# note that we can also place "ON DELETE CASCADE" on the tables themselves,
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# instead of using this extension
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class DeleteMemberExt(MapperExtension):
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"""will delete child Member objects in one pass when Organizations are deleted"""
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def before_delete(self, mapper, connection, instance):
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connection.execute(member_table.delete(member_table.c.org_id==instance.org_id))
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mapper(Organization, org_table, extension=DeleteMemberExt(), properties = {
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# set up the relationship with "lazy=None" so no loading occurs (even lazily),
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# "cascade='all, delete-orphan'" to declare Member objects as local to their parent Organization,
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# "passive_deletes=True" so that the "delete, delete-orphan" cascades do not load in the child objects
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# upon deletion
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'members' : relation(Member, lazy=None, passive_deletes=True, cascade="all, delete-orphan")
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})
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mapper(Member, member_table)
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sess = create_session()
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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.save(org)
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print "-------------------------\nflush one - save org + 3 members"
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sess.flush()
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sess.clear()
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# reload. load the org and some child members
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print "-------------------------\nload subset of members"
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org = sess.query(Organization).get(org.org_id)
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members = org.member_query.filter(member_table.c.name.like('%member t%')).all()
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print members
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sess.clear()
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# reload. create some more members and flush, without loading any of the original members
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org = sess.query(Organization).get(org.org_id)
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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"
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sess.flush()
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sess.clear()
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org = sess.query(Organization).get(org.org_id)
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# now delete. note that this will explictily delete members four, five and six because they are in the session,
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# but will not issue individual deletes for members one, two and three, nor will it load them.
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sess.delete(org)
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print "-------------------------\nflush three - delete org, delete members in one statement"
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sess.flush()
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