Question

I’d like to use regexp query in “sqlalchemy” as well as is done in “python sqlite”, code below..

Unfinished sandbox script is this:

import os
import re
import sqlite3

#
# python sqlite
#

DB_PATH = __name__ + '.db'

try:
    os.remove(DB_PATH)
except:
    pass


def re_fn(expr, item):
    reg = re.compile(expr, re.I)
    return reg.search(item) is not None

conn = sqlite3.connect(':memory:')
conn = sqlite3.connect(DB_PATH)
conn.create_function("REGEXP", 2, re_fn)
cursor = conn.cursor()

cursor.execute(
    'CREATE TABLE t1 (id INTEGER PRIMARY KEY, c1 TEXT)'
)
cursor.executemany(
    #'INSERT INTO t1 (c1) VALUES (?)', [('aaa"test"',),('blah',)]
    'INSERT INTO t1 (c1) VALUES (?)', [
        ('dupa / 1st Part',), ('cycki / 2nd Part',), ('fiut / 3rd Part',)
    ]
)
cursor.execute(
    #'SELECT c1 FROM t1 WHERE c1 REGEXP ?',['2|3\w+part']
    'SELECT c1 FROM t1 WHERE c1 REGEXP ?',['\d\w+ part']
)
conn.commit()
data=cursor.fetchall()
print(data)



#
# sqlalchemy
#

import sqlalchemy as sa
import sqlalchemy.orm as orm
from sqlalchemy.ext.declarative import declarative_base

DSN = 'sqlite:///' + DB_PATH
engine = sa.create_engine(DSN, convert_unicode=True)
db = orm.scoped_session(orm.sessionmaker(autocommit=False,
                                         autoflush=False,
                                         bind=engine))

Base = declarative_base(bind=engine)
meta = Base.metadata

class T1(Base):
    __table__ = sa.Table('t1', meta, autoload=True)

print(db.query(T1).all())

I’ve found that regexp function should be registered on each thread:

http://permalink.gmane.org/gmane.comp.web.pylons.general/12742

but I’m not able to adopt link’s solution to my script + it’s deprecated.

Update

I’d like to query this:

cursor.execute(
    #'SELECT c1 FROM t1 WHERE c1 REGEXP ?',['2|3\w+part']
    'SELECT c1 FROM t1 WHERE c1 REGEXP ?',['\d\w+ part']
)

but in sqlalchemy.

Answer 1

I’ve got the answer..
Complete working script with missing one line is this:

import os
import re
import sqlite3

DB_PATH = __name__ + '.db'

try:
    os.remove(DB_PATH)
except:
    pass


def re_fn(expr, item):
    reg = re.compile(expr, re.I)
    return reg.search(item) is not None

conn = sqlite3.connect(':memory:')
conn = sqlite3.connect(DB_PATH)
conn.create_function("REGEXP", 2, re_fn)
cursor = conn.cursor()

cursor.execute(
    'CREATE TABLE t1 (id INTEGER PRIMARY KEY, c1 TEXT)'
)
cursor.executemany(
    #'INSERT INTO t1 (c1) VALUES (?)', [('aaa"test"',),('blah',)]
    'INSERT INTO t1 (c1) VALUES (?)', [
        ('dupa / 1st Part',), ('cycki / 2nd Part',), ('fiut / 3rd Part',)
    ]
)
SEARCH_TERM = '3rd part'
cursor.execute(
    #'SELECT c1 FROM t1 WHERE c1 REGEXP ?',['2|3\w+part']
    'SELECT c1 FROM t1 WHERE c1 REGEXP ?',[SEARCH_TERM]
)
conn.commit()
data=cursor.fetchall()
print(data)



#
# sqlalchemy
#

import sqlalchemy as sa
import sqlalchemy.orm as orm
from sqlalchemy.ext.declarative import declarative_base

DSN = 'sqlite:///' + DB_PATH

engine = sa.create_engine(DSN, convert_unicode=True)

conn = engine.connect()
conn.connection.create_function('regexp', 2, re_fn)

db = orm.scoped_session(orm.sessionmaker(autocommit=False,
                                         autoflush=False,
                                         bind=engine))

Base = declarative_base(bind=engine)
meta = Base.metadata

class T1(Base):
    __table__ = sa.Table('t1', meta, autoload=True)

print(db.query(T1.c1).filter(T1.c1.op('regexp')(SEARCH_TERM)).all())

Above works in sqlalchemy=0.6.3

In sqlalchemy=0.7.8 i got error:

“sqlalchemy.exc.OperationalError: (OperationalError) no such function:
regexp ..”

maybe because of this change:

When a file-based database is specified, the dialect will use NullPool
as the source of connections. This pool closes and discards
connections which are returned to the pool immediately. SQLite
file-based connections have extremely low overhead, so pooling is not
necessary. The scheme also prevents a connection from being used again
in a different thread and works best with SQLite’s coarse-grained file
locking.
Changed in version 0.7: Default selection of NullPool for SQLite
file-based databases. Previous versions select SingletonThreadPool by
default for all SQLite databases.

from: http://docs.sqlalchemy.org/en/rel_0_7/dialects/sqlite.html?highlight=isolation_level#threading-pooling-behavior

and solution for that was:
to add regexp fn in ‘begin’ event like this:

...

conn = engine.connect()
@sa.event.listens_for(engine, "begin")
def do_begin(conn):
    conn.connection.create_function('regexp', 2, re_fn)

db = orm.scoped_session(orm.sessionmaker(autocommit=False,
                                         autoflush=False,
                                         bind=engine))

...