mirror of
https://github.com/sqlalchemy/sqlalchemy.git
synced 2026-05-09 02:09:53 -04:00
Federico Caselli
e860060866
This change includes mainly that the bracketed use within select() is moved to positional, and keyword arguments are removed from calls to the select() function. it does not yet fully address other issues such as keyword arguments passed to the table.select(). Additionally, allows False / None to both be considered as "disable" for all of select.correlate(), select.correlate_except(), query.correlate(), which establishes consistency with passing of ``False`` for the legact select(correlate=False) argument. Change-Id: Ie6c6e6abfbd3d75d4c8de504c0cf0159e6999108
136 lines
3.7 KiB
Python
136 lines
3.7 KiB
Python
"""Celko's "Nested Sets" Tree Structure.
|
|
|
|
http://www.intelligententerprise.com/001020/celko.jhtml
|
|
|
|
"""
|
|
|
|
from sqlalchemy import case
|
|
from sqlalchemy import Column
|
|
from sqlalchemy import create_engine
|
|
from sqlalchemy import event
|
|
from sqlalchemy import func
|
|
from sqlalchemy import Integer
|
|
from sqlalchemy import select
|
|
from sqlalchemy import String
|
|
from sqlalchemy.ext.declarative import declarative_base
|
|
from sqlalchemy.orm import aliased
|
|
from sqlalchemy.orm import Session
|
|
|
|
|
|
Base = declarative_base()
|
|
|
|
|
|
class Employee(Base):
|
|
__tablename__ = "personnel"
|
|
__mapper_args__ = {
|
|
"batch": False # allows extension to fire for each
|
|
# instance before going to the next.
|
|
}
|
|
|
|
parent = None
|
|
|
|
emp = Column(String, primary_key=True)
|
|
|
|
left = Column("lft", Integer, nullable=False)
|
|
right = Column("rgt", Integer, nullable=False)
|
|
|
|
def __repr__(self):
|
|
return "Employee(%s, %d, %d)" % (self.emp, self.left, self.right)
|
|
|
|
|
|
@event.listens_for(Employee, "before_insert")
|
|
def before_insert(mapper, connection, instance):
|
|
if not instance.parent:
|
|
instance.left = 1
|
|
instance.right = 2
|
|
else:
|
|
personnel = mapper.mapped_table
|
|
right_most_sibling = connection.scalar(
|
|
select(personnel.c.rgt).where(
|
|
personnel.c.emp == instance.parent.emp
|
|
)
|
|
)
|
|
|
|
connection.execute(
|
|
personnel.update(personnel.c.rgt >= right_most_sibling).values(
|
|
lft=case(
|
|
[
|
|
(
|
|
personnel.c.lft > right_most_sibling,
|
|
personnel.c.lft + 2,
|
|
)
|
|
],
|
|
else_=personnel.c.lft,
|
|
),
|
|
rgt=case(
|
|
[
|
|
(
|
|
personnel.c.rgt >= right_most_sibling,
|
|
personnel.c.rgt + 2,
|
|
)
|
|
],
|
|
else_=personnel.c.rgt,
|
|
),
|
|
)
|
|
)
|
|
instance.left = right_most_sibling
|
|
instance.right = right_most_sibling + 1
|
|
|
|
# before_update() would be needed to support moving of nodes
|
|
# after_delete() would be needed to support removal of nodes.
|
|
|
|
|
|
engine = create_engine("sqlite://", echo=True)
|
|
|
|
Base.metadata.create_all(engine)
|
|
|
|
session = Session(bind=engine)
|
|
|
|
albert = Employee(emp="Albert")
|
|
bert = Employee(emp="Bert")
|
|
chuck = Employee(emp="Chuck")
|
|
donna = Employee(emp="Donna")
|
|
eddie = Employee(emp="Eddie")
|
|
fred = Employee(emp="Fred")
|
|
|
|
bert.parent = albert
|
|
chuck.parent = albert
|
|
donna.parent = chuck
|
|
eddie.parent = chuck
|
|
fred.parent = chuck
|
|
|
|
# the order of "add" is important here. elements must be added in
|
|
# the order in which they should be INSERTed.
|
|
session.add_all([albert, bert, chuck, donna, eddie, fred])
|
|
session.commit()
|
|
|
|
print(session.query(Employee).all())
|
|
|
|
# 1. Find an employee and all their supervisors, no matter how deep the tree.
|
|
ealias = aliased(Employee)
|
|
print(
|
|
session.query(Employee)
|
|
.filter(ealias.left.between(Employee.left, Employee.right))
|
|
.filter(ealias.emp == "Eddie")
|
|
.all()
|
|
)
|
|
|
|
# 2. Find the employee and all their subordinates.
|
|
# (This query has a nice symmetry with the first query.)
|
|
print(
|
|
session.query(Employee)
|
|
.filter(Employee.left.between(ealias.left, ealias.right))
|
|
.filter(ealias.emp == "Chuck")
|
|
.all()
|
|
)
|
|
|
|
# 3. Find the level of each node, so you can print the tree
|
|
# as an indented listing.
|
|
for indentation, employee in (
|
|
session.query(func.count(Employee.emp).label("indentation") - 1, ealias)
|
|
.filter(ealias.left.between(Employee.left, Employee.right))
|
|
.group_by(ealias.emp)
|
|
.order_by(ealias.left)
|
|
):
|
|
print(" " * indentation + str(employee))
|