[storm] This is a noob question: storing lists

[James Henstridge]

On Thu, May 7, 2009 at 2:09 PM, chandramouli s <naruvimama at gmail.com> wrote:
> What I would like to do is store a set of data values, 400 or so in a
> sqlite database (instead of a flatfile as it is normally done). And I
> tried to run following  the examples, but I wonder if the list storage
> is right. Any help is much appreciated
>
> The program:
> ############################################################
>
> from storm.locals import *
> class Personner(object):
>  __storm_table__="personner"
>  id= Int(primary=True)
>  name=Unicode()
>  marks=List()

If you want to use the List() property, you should specify what the
list holds.  For example:

    marks = List(type=Int())

That said, I'm not sure how well sqlite handles arrays, so it might be
appropriate to do something else.


> database=create_database("sqlite:///fort")
> store=Store(database)
> store.execute("CREATE TABLE IF NOT EXISTS personner (id INTEGER
> PRIMARY KEY, name VARCHAR,marks TEXT)")
> for x in xrange(200):
>  d=Personner()
>  d.name=unicode(str(x))

The double cast here is unneeded.  If you want a unicode
representation of an integer, just do unicode(x).

>  d.marks=[x,2*x,x-1,x*6] # d.marks=unicode(str([x,2*x,x-1,x*6]))
>  store.add(d)
>  store.flush()
>  print 'success'
>
> store.commit()
> print 'done'
>
> #####################################################################
> The error msg:
> Traceback (most recent call last):
>  File "testStorm.py", line 16, in <module>
>    store.flush()
>  File "/usr/lib64/python2.6/site-packages/storm/store.py", line 486, in flush
>    self._flush_one(obj_info)
>  File "/usr/lib64/python2.6/site-packages/storm/store.py", line 523,
> in _flush_one
>    result = self._connection.execute(expr)
>  File "/usr/lib64/python2.6/site-packages/storm/database.py", line
> 203, in execute
>    raw_cursor = self.raw_execute(statement, params)
>  File "/usr/lib64/python2.6/site-packages/storm/databases/sqlite.py",
> line 153, in raw_execute
>    return Connection.raw_execute(self, statement, params)
>  File "/usr/lib64/python2.6/site-packages/storm/database.py", line
> 284, in raw_execute
>    self._check_disconnect(raw_cursor.execute, *args)
>  File "/usr/lib64/python2.6/site-packages/storm/database.py", line
> 325, in _check_disconnect
>    return function(*args, **kwargs)
> pysqlite2.dbapi2.InterfaceError: Error binding parameter 0 - probably
> unsupported type.

If this error still happens after changing the property definition, it
means you'll have to pick another approach.  Some things to try:

1. manually encode/decode the lists of integers when storing them to the DB.
2. use a Pickle() column, which lets you store arbitrary objects
(doesn't constrain data much, and is not particularly efficient).
3. Add a second table to store individual marks, referencing the first
table in a many to one relationship.  If you ever want to search based
on the marks values, then this is probably what you want.

James.