pylons.database does not provide a way to set the SQLAlchemy
connection options beyond 'echo'. But MySQL needs 'pool_recycle'
[1], and users may want to set other options in their config. I tried
a few different ways and eventually came up with this. It adds
"sqlalchemy.pool_recycle" and "sqlalchemy.echo_pool", and is
expandable for other options. Would this approach be suitable for
pylons.database? If so I'll make a Trac patch.
Two differences:
get_engine_conf() returns a dict of args for
sqlalchemy.create_engine() rather than a tuple of (uri, echo).
create_engine(), get_engine_conf(), and make_session() do not accept
args. In pylons.database they take optional 'url' and 'echo' args
which override the values in the config file. Does anybody actually
use this feature? If so, I could make them take an arbitrary set of
**engine_args, which get_engine_conf() would not look up in the config
file.
[1] MySQL 5 unilaterally closes connections after N hours of idle
time, causing applications to raise a "mysql server has gone away"
exception if they later use the connection. N is 8 by default; you
can set it in my.cnf but you can't disable it. My existing Quixote
applications have a module-level connection so I restart them every 12
hours. Having connections that automatically get recreated after a
few hours is my main motivation for moving to SQLAlchemy.
--
Mike Orr <[EMAIL PROTECTED]>
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from paste.deploy.converters import asbool
from pylons.database import app_scope, get_engines
import pylons.util
import sqlalchemy
from sqlalchemy.ext import sessioncontext
__all__ = [
"app_scope",
"create_engine",
"get_engine_conf",
"get_engines",
"make_session",
"session_context",
]
def create_engine():
"""Create a SQLAlchemy db engine.
Unlike pylons.database.create_engine, this version does not accept
'uri' or 'echo' args.
"""
engine_conf = get_engine_conf()
# Extract 'uri' to avoid exception in sqlalchemy.create_engine().
uri = engine_conf.pop("uri")
engine = sqlalchemy.create_engine(uri, **engine_conf)
return engine
def get_engine_conf():
"""A version of pylons.database.get_engine_conf() with more config options.
Return a dict of arguments suitable for sqlalchemy.create_engine().
Unlike pylons.database.get_engine_conf, this version does not accept
'uri' or 'echo' args. It also fixes a parsing bug on the 'echo' var.
"""
cg = pylons.util.config_get
conf = {}
conf["uri"] = cg("sqlalchemy.dburi")
if not conf["uri"]:
raise KeyError("config var 'sqlalchemy.dburi' is required")
conf["echo"] = asbool(cg("sqlalchemy.echo", False))
conf["echo_pool"] = asbool(cg("sqlalchemy.echo_pool", False))
conf["pool_recycle"] = int(cg("sqlalchemy.pool_recycle", -1)) # Raises ValueError
return conf
def make_session():
"""Return a SQLAlchemy session
Unlike pylons.database.make_session, this version does not accept
'uri' or 'echo' args.
"""
uri = pylons.util.config_get("sqlalchemy.dburi")
db_engines = get_engines()
if uri in db_engines:
engine = db_engines[uri]
else:
engine = db_engines[uri] = create_engine()
return sqlalchemy.create_session(bind_to=engine)
session_context = sessioncontext.SessionContext(make_session,
scopefunc=app_scope)
