mirror of
https://github.com/sqlalchemy/sqlalchemy.git
synced 2026-05-28 03:26:01 -04:00
Mike Bayer
580139598f
This is a straight reformat run using black as is, with no edits applied at all. The black run will format code consistently, however in some cases that are prevalent in SQLAlchemy code it produces too-long lines. The too-long lines will be resolved in the following commit that will resolve all remaining flake8 issues including shadowed builtins, long lines, import order, unused imports, duplicate imports, and docstring issues. Change-Id: I7eda77fed3d8e73df84b3651fd6cfcfe858d4dc9
136 lines
3.6 KiB
Python
136 lines
3.6 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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create_engine,
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Column,
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Integer,
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String,
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select,
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case,
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func,
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)
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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]).where(
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personnel.c.emp == instance.parent.emp
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)
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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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[
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(
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personnel.c.lft > right_most_sibling,
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personnel.c.lft + 2,
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)
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],
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else_=personnel.c.lft,
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),
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rgt=case(
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[
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(
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personnel.c.rgt >= right_most_sibling,
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personnel.c.rgt + 2,
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)
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],
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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(
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session.query(Employee)
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.filter(ealias.left.between(Employee.left, Employee.right))
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.filter(ealias.emp == "Eddie")
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.all()
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)
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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(
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session.query(Employee)
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.filter(Employee.left.between(ealias.left, ealias.right))
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.filter(ealias.emp == "Chuck")
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.all()
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)
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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 (
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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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):
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print(" " * indentation + str(employee))
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