Hello again,
I have recently noticed that a particular assignment seems to be
taking a "relatively" long time.
Not being a database expert I am confused as to whether the last
assignment 'person.tags = tags' should be so slow when referencing
existing tags that are used by other entities - it seems to try and
get a list of all employees that use the given tag and then spends the
time doing something with the resulting set, but why?
Test case below.
If the slow assignment is expected do you have any advice on how to
speed up such a statement?
Thank you in advance,
Martin
----------------------------------------------------------------------------------
import os, datetime, time
from sqlalchemy import *
from sqlalchemy.orm import *
file = '/tmp/test.db'
if os.path.isfile(file): os.remove(file)
engine = create_engine('sqlite:///%s' % file, echo=True)
metadata = MetaData()
Session = scoped_session(sessionmaker(autoflush=True,
transactional=False, bind=engine))
mapper = Session.mapper
# Classes
#----------------------------------------------
class Employee(object):
def __init__(self, name=None):
self.name = name
def __repr__(self):
return '%s:%s' % (self.id, self.name)
class Tag(object):
def __init__(self, label):
self.label = label
# Setup tables
#----------------------------------------------
employees = Table('employees', metadata,
Column('id', Integer, primary_key=True),
Column('name', String, nullable=False,
default='bob'),
Column('dob', DateTime, nullable=False,
default=datetime.datetime.now),
)
tags = Table('tags', metadata,
Column('id', Integer, primary_key=True),
Column('label', String, nullable=False),
)
employeesTags = Table('employeesTags', metadata,
Column('employee_id', Integer,
ForeignKey('employees.id')),
Column('tag_id', Integer,
ForeignKey('tags.id')),
)
# Mappers
#----------------------------------------------
mapper(Employee, employees, properties={
'tags': relation(Tag, secondary=employeesTags,
backref='employees', lazy=False)
})
mapper(Tag, tags)
# Test
#----------------------------------------------
metadata.create_all(engine)
session = Session()
session.begin()
tags = []
for i in xrange(20):
tag = Tag(str(datetime.datetime.now()))
tags.append(tag)
for i in xrange(1000):
p = Employee('john%d' % i)
p.tags = tags
session.commit()
session.clear()
session.begin()
tags = session.query(Tag).all()[:2]
person = Employee('bob')
started = time.time()
person.tags = tags
print 'Took:', time.time()-started
session.commit()
session.clear()
Session.remove()
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