mirror of
https://github.com/sqlalchemy/sqlalchemy.git
synced 2026-05-07 01:10:52 -04:00
Mike Bayer
d80ee72aaa
standalone gendered pronoun with a gender-neutral subject, but also have replaced all occurences of "his/her", "his or her", etc. The docs have always strived to account for both genders in any non-specific singular pronoun, however recent controversy in the community suggests that a zero-gendered-pronoun policy is probably best going forward.
112 lines
3.4 KiB
Python
112 lines
3.4 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 (create_engine, Column, Integer, String, select, case,
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func)
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from sqlalchemy.orm import Session, aliased
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from sqlalchemy.ext.declarative import declarative_base
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from sqlalchemy import event
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Base = declarative_base()
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class Employee(Base):
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__tablename__ = 'personnel'
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__mapper_args__ = {
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'batch': False # allows extension to fire for each
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# 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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@event.listens_for(Employee, "before_insert")
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def before_insert(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]).
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where(personnel.c.emp == instance.parent.emp)
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)
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connection.execute(
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personnel.update(
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personnel.c.rgt >= right_most_sibling).values(
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lft=case(
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[(personnel.c.lft > right_most_sibling,
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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,
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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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engine = create_engine('sqlite://', echo=True)
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Base.metadata.create_all(engine)
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session = Session(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 their 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 their subordinates.
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# (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
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# as an indented listing.
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for indentation, employee in session.query(
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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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