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Date: Fri, 28 Mar 2014 15:16:05 +0100
From: Daniele Forghieri <guru@digitalfantasy.it>
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To: python-list@python.org
Subject: Re: Using query parameters subtitution outside of execute()
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Il 28/03/2014 14:53, Peter Otten ha scritto:
> Daniele Forghieri wrote:
>
>> Il 28/03/2014 10:16, Peter Otten ha scritto:
>>> Daniele Forghieri wrote:
>>>
>>>> Hi to all. I'm using sqlite3 with python 2.7 on windows.
>>>>
>>>> I use the query substitution parameters in my query but I need to pass
>>>> part of the query to a function, something like (it's not the real
>>>> examples, just to clarify the question):
>>>>
>>>> def loadAll(cursor, id, queryAdd = None):
>>>>        if queryAdd is None:
>>>>            qry =  'select * from files where catalog = ?'
>>>>        else:
>>>>            qry = 'select * from files where catalog = ? and %s' %
>>>>            (queryAdd))
>>>>
>>>>        cursor.execute(qry, (id, ))
>>>>        ...
>>>>
>>>> I would like to use the query substitution even when I create, in
>>>> another piece of code, the queryAdd part, something like:
>>>>
>>>> queryAdd = cursor.querySubst('enabled = ? and hide = ? and data > ?',
>>>> (enabled, hidden, min_date, ))
>>>>
>>>> when the function take care of the date format, quoting the parameter
>>>> and so on
>>>>
>>>> It's possible or not ?
>>> You can use named parameters
>>>
>>> http://docs.python.org/dev/library/sqlite3.html#cursor-objects
>>>
>>> Your function might become (untested)
>>>
>>> def load_all(cursor, parameters, condition="catalog = :id"):
>>>       query =  'select * from files where ' + condition
>>>       cursor.execute(query, parameters)
>>>       ...
>>>
>>> load_all(
>>>       cursor, dict(id=42, fromdate=datetime.date.today()),
>>>       condition="catalog = :id and date >= :fromdate")
>>>
>>       Thank. With this I can solve the problem but I have to specify the
>> query twice and if I have to change something I need to made it
>> everywhere I use the function and is something I would like to avoid.
> How about that one:
>
> def query_subst(sql, parameters):
>      return sql, parameters
>
> def load_all(cursor, id, query_add=None):
>      query =  'select * from files where catalog = ?'
>      parameters = (id,)
>      if query_add is not None:
>          query += " and " + query_add[0]
>          parameters += query_add[1]
>      cursor.execute(query, parameters)
>      ...
>
> enabled = True
> hidden = False
> min_date = datetime.date.today()
>
> query_add = query_subst(
>      'enabled = ? and hide = ? and date > ?',
>      (enabled, hidden, min_date))
>
> load_all(cs, 42, query_add)

     This one is, IMHO, cleaner and more manageable!

     Thank you very very much, I really appreciate your help.

>>       I also don't like very mush to pass or create a dict for a function
>> call but that's probably me coming from old plain C ;)
> Get over it ;)
>
>

         I'm trying but the old habits comes out, the first time I need 
to parse a string I do it like in C, looking at every single char using 
a couple of help function: the performance were really horrible, the 
memory used was huge than I change the way I do things (and start to use 
sqlite3 to store my data instead of using text files, parsed by a 
proprietary lib).

         The worse is the contrary, when I must use C and I think 'Here 
I use a dictionary, at the end convert it in a list that I sort with 
that key ...' only to realize that I don't have dictionary and the list 
I can use are very less manageable that the ones I used in Python ...

         It seems to me that going from C to Python you start writing 
inefficient code or write more lines than an average Python programmer 
but 'something moves' and the result happens. Moving from Python to C I 
always feel like I missed something and the first approach, good for 
Python, is simply not working in C ;(

     Thanks again

     Daniele Forghieri