mirror of
https://github.com/sqlalchemy/sqlalchemy.git
synced 2026-05-11 11:22:15 -04:00
Mike Bayer
a5dfbeedb9
accurately adapt the expressions generated, which helps particularly with self-referential comparisons. [ticket:1171] - Fixed bug involving primaryjoin/secondaryjoin conditions constructed from class-bound attributes (as often occurs when using declarative), which later would be inappropriately aliased by Query, particularly with the various EXISTS based comparators.
104 lines
3.5 KiB
Python
104 lines
3.5 KiB
Python
"""Celko's "Nested Sets" Tree Structure.
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http://www.intelligententerprise.com/001020/celko.jhtml
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"""
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from sqlalchemy import *
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from sqlalchemy.orm import *
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from sqlalchemy.orm import attributes
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from sqlalchemy.ext.declarative import declarative_base
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engine = create_engine('sqlite://', echo=True)
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Base = declarative_base()
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class NestedSetExtension(MapperExtension):
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def before_insert(self, mapper, connection, instance):
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if not instance.parent:
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instance.left = 1
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instance.right = 2
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else:
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personnel = mapper.mapped_table
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right_most_sibling = connection.scalar(
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select([personnel.c.rgt]).where(personnel.c.emp==instance.parent.emp)
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)
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connection.execute(
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personnel.update(personnel.c.rgt>=right_most_sibling).values(
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lft = case(
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[(personnel.c.lft>right_most_sibling, personnel.c.lft + 2)],
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else_ = personnel.c.lft
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),
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rgt = case(
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[(personnel.c.rgt>=right_most_sibling, personnel.c.rgt + 2)],
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else_ = personnel.c.rgt
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)
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)
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)
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instance.left = right_most_sibling
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instance.right = right_most_sibling + 1
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# before_update() would be needed to support moving of nodes
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# after_delete() would be needed to support removal of nodes.
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# [ticket:1172] needs to be implemented for deletion to work as well.
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class Employee(Base):
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__tablename__ = 'personnel'
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__mapper_args__ = {
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'extension':NestedSetExtension(),
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'batch':False # allows extension to fire for each instance before going to the next.
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}
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parent = None
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emp = Column(String, primary_key=True)
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left = Column("lft", Integer, nullable=False)
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right = Column("rgt", Integer, nullable=False)
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def __repr__(self):
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return "Employee(%s, %d, %d)" % (self.emp, self.left, self.right)
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Base.metadata.create_all(engine)
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session = sessionmaker(bind=engine)()
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albert = Employee(emp='Albert')
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bert = Employee(emp='Bert')
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chuck = Employee(emp='Chuck')
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donna = Employee(emp='Donna')
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eddie = Employee(emp='Eddie')
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fred = Employee(emp='Fred')
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bert.parent = albert
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chuck.parent = albert
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donna.parent = chuck
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eddie.parent = chuck
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fred.parent = chuck
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# the order of "add" is important here. elements must be added in
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# the order in which they should be INSERTed.
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session.add_all([albert, bert, chuck, donna, eddie, fred])
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session.commit()
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print session.query(Employee).all()
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# 1. Find an employee and all his/her supervisors, no matter how deep the tree.
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ealias = aliased(Employee)
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print session.query(Employee).\
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filter(ealias.left.between(Employee.left, Employee.right)).\
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filter(ealias.emp=='Eddie').all()
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#2. Find the employee and all his/her subordinates. (This query has a nice symmetry with the first query.)
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print session.query(Employee).\
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filter(Employee.left.between(ealias.left, ealias.right)).\
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filter(ealias.emp=='Chuck').all()
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#3. Find the level of each node, so you can print the tree as an indented listing.
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for indentation, employee in session.query(func.count(Employee.emp).label('indentation') - 1, ealias).\
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filter(ealias.left.between(Employee.left, Employee.right)).\
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group_by(ealias.emp).\
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order_by(ealias.left):
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print " " * indentation + str(employee)
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