[sqlalchemy] newbie question: best way to factor and group data when only some columns change

[Robert Henry]

I have a tester that controls 30 independent variables.  Each variable can 
have about 40 different values.

Periodically, I run a test. I choose 2 of the 30 independent variables, and 
over the next few minutes, fully iterate those 2 variables relative to each 
other, visiting each point in a 40*40 space.  I want to record the result 
of the test at each of those 40*40 points.

What's the best way to use sqlalchemy+mysql to represent this use case?  
I'm not even sure of the terminology to use describing this factoring to 
use for Google searching.

I'm inclined to have a separate table for each test run, where that table 
records {param1 value, param2 value, date, result} and then have a master 
table, one row per test run, where that row holds the value of all 30 
variables, lists the 2 control variables, and then somehow references or 
names the separate table with the results of the test run.

Robert Henry

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[sqlalchemy] Newbie Question: Aliases not Aliasing?

[Haoyi Li]

I posted this 
questionhttp://stackoverflow.com/questions/16410888/sqlalchemy-aliases-not-aliasingto
 StackOverflow, but thought this may be a better place to ask.

I have the following sqlalchemy code:

x = bbc.alias().c
w = bbc.alias().cselect([func.distinct(x.region)]).where(
select([func.sum(w.population)]).where((w.region == x.region))  1)

I would expect it to produce this SQL:

SELECT DISTINCT(x.region)FROM bbc xWHERE 1  (
SELECT SUM(w.population)
from bbc w
WHERE w.region = x.region)

but instead it gives me this:

SELECT distinct(bbc_1.region) AS distinct_1 FROM bbc AS bbc_1 WHERE 1

Somehow the WHERE clause is collapsing, but for the life of me I can't see 
why. Am I doing something wrong with the aliases?

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Re: [sqlalchemy] Newbie Question: Aliases not Aliasing?

[Michael Bayer]

update the SO question too for me...in this case it needs a clue to interpret 
the select as a scalar:

subq = select([func.sum(w.population)]).where((w.region == x.region))

print select([func.distinct(x.region)]).where(subq.as_scalar()  1)

the WHERE 1 you're getting is because someselect  1 just comes out to 
Python True.




On May 7, 2013, at 9:58 AM, Haoyi Li haoyi...@gmail.com wrote:

 I posted this question to StackOverflow, but thought this may be a better 
 place to ask.
 
 I have the following sqlalchemy code:
 
 x = bbc.alias().c
 w = bbc.alias().c
 select([func.distinct(x.region)]).where(
 select([func.sum(w.population)]).where((w.region == x.region))  1
 )
 I would expect it to produce this SQL:
 
 SELECT DISTINCT(x.region)
 FROM bbc x
 WHERE 1  (
 SELECT SUM(w.population)
 from bbc w
 WHERE w.region = x.region
 )
 but instead it gives me this:
 
 SELECT distinct(bbc_1.region) AS distinct_1 
 FROM bbc AS bbc_1 
 WHERE 1
 Somehow the WHERE clause is collapsing, but for the life of me I can't see 
 why. Am I doing something wrong with the aliases?
 
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Re: [sqlalchemy] Newbie Question: Aliases not Aliasing?

[Haoyi Li]

Thanks, that worked!

A follow up question to make sure i'm understanding this right: I'm looking 
at the effect of .as_scalar() on the query, and it seems that any query I 
call .as_scalar() on simply gets wrapped in parenthesis. I tested it out 
and it seems that it works even in cases where I don't want a scalar value 
(e.g. thing._in(myquery.as_scalar()) ), which kind of aligns with my 
theory that it just wraps stuff in parenthesis. Is that all it does, or 
does it do something more? It doesn't work on the top level query, but 
would it be safe to simply wrap all the nested queries with a 
(...).as_scalar()?

Thanks!
-Haoyi

On Tuesday, May 7, 2013 11:53:52 AM UTC-4, Michael Bayer wrote:

 update the SO question too for me...in this case it needs a clue to 
 interpret the select as a scalar:

 subq = select([func.sum(w.population)]).where((w.region == x.region))

 print select([func.distinct(x.region)]).where(subq.as_scalar()  1)

 the WHERE 1 you're getting is because someselect  1 just comes 
 out to Python True.




 On May 7, 2013, at 9:58 AM, Haoyi Li haoy...@gmail.com javascript: 
 wrote:

 I posted this 
 questionhttp://stackoverflow.com/questions/16410888/sqlalchemy-aliases-not-aliasingto
  StackOverflow, but thought this may be a better place to ask.

 I have the following sqlalchemy code:

 x = bbc.alias().c
 w = bbc.alias().cselect([func.distinct(x.region)]).where(
 select([func.sum(w.population)]).where((w.region == x.region))  
 1)

 I would expect it to produce this SQL:

 SELECT DISTINCT(x.region)FROM bbc xWHERE 1  (
 SELECT SUM(w.population)
 from bbc w
 WHERE w.region = x.region)

 but instead it gives me this:

 SELECT distinct(bbc_1.region) AS distinct_1 FROM bbc AS bbc_1 WHERE 1

 Somehow the WHERE clause is collapsing, but for the life of me I can't see 
 why. Am I doing something wrong with the aliases?

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Re: [sqlalchemy] Newbie Question: Aliases not Aliasing?

[Michael Bayer]

it's a Python thing, it turns the FromClause into a ColumnElement which then 
has operators like __eq__(), __lt__(), etc.


On May 7, 2013, at 2:29 PM, Haoyi Li haoyi...@gmail.com wrote:

 Thanks, that worked!
 
 A follow up question to make sure i'm understanding this right: I'm looking 
 at the effect of .as_scalar() on the query, and it seems that any query I 
 call .as_scalar() on simply gets wrapped in parenthesis. I tested it out and 
 it seems that it works even in cases where I don't want a scalar value (e.g. 
 thing._in(myquery.as_scalar()) ), which kind of aligns with my theory that 
 it just wraps stuff in parenthesis. Is that all it does, or does it do 
 something more? It doesn't work on the top level query, but would it be safe 
 to simply wrap all the nested queries with a (...).as_scalar()?
 
 Thanks!
 -Haoyi
 
 On Tuesday, May 7, 2013 11:53:52 AM UTC-4, Michael Bayer wrote:
 update the SO question too for me...in this case it needs a clue to interpret 
 the select as a scalar:
 
 subq = select([func.sum(w.population)]).where((w.region == x.region))
 
 print select([func.distinct(x.region)]).where(subq.as_scalar()  1)
 
 the WHERE 1 you're getting is because someselect  1 just comes out 
 to Python True.
 
 
 
 
 On May 7, 2013, at 9:58 AM, Haoyi Li haoy...@gmail.com wrote:
 
 I posted this question to StackOverflow, but thought this may be a better 
 place to ask.
 
 I have the following sqlalchemy code:
 
 x = bbc.alias().c
 w = bbc.alias().c
 select([func.distinct(x.region)]).where(
 select([func.sum(w.population)]).where((w.region == x.region))  
 1
 )
 I would expect it to produce this SQL:
 
 SELECT DISTINCT(x.region)
 FROM bbc x
 WHERE 1  (
 SELECT SUM(w.population)
 from bbc w
 WHERE w.region = x.region
 )
 but instead it gives me this:
 
 SELECT distinct(bbc_1.region) AS distinct_1 
 FROM bbc AS bbc_1 
 WHERE 1
 Somehow the WHERE clause is collapsing, but for the life of me I can't see 
 why. Am I doing something wrong with the aliases?
 
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Re: [sqlalchemy] Newbie question

[Kent Tenney]

On Wed, Jul 27, 2011 at 2:48 PM, Michael Bayer mike...@zzzcomputing.com wrote:

 On Jul 27, 2011, at 3:21 PM, Kent Tenney wrote:

 Howdy,

 I'm aggregating data from several Sqlite files into a Postgres db.
 The sqlite files are storage for several apps I use: Shotwell,
 Firefox, Zotero, Banshee ... I just watch and pull from them.

 I've been using import sqlite3 so far, dumping sql from sqlite,
 using it to create the Postgres tables. I then add columns to meet
 my own needs. I now can diff 2 sqlite files, so I know what rows
 need updating and adding in the Postgres tables.

 I feel I should be using Sqlalchemy,

 ok well what problems do you have currently that you'd like to solve ?

With some proof-of-concept working, looking ahead to increasing
complexity, my sense is that SA can hide some complexity behind
a layer which moves data into Postgres. I think this is what you
suggest in your final paragraph.



 but have been intimidated by
 the wealth of choices SA offers.

 It offers choices in that you can A. use core only or B. the ORM, as well 
 as choices in that it works with whatever kind of schema you'd like,

I'll be studying doc for a better idea of the A/B distinction, as
well as what kinds of schemas there are.

I have the O'Reilly book, I understand SA has changed considerably
since then, am I better off sticking with current doc?

 which is the same choice you have anyway, and in this case it seems
you have already made.     Your app sounds like kind of a nuts and
bolts table-to-table thing, i.e. is SQL centric, so using constructs
like table.select() and table.insert() could perhaps reduce the
verbosity of generating those statements by hand, the Table construct
itself can turn the equation of what columns am i dealing with here?
into a data driven one (the Table is a datastructure, which stores a
list of Column objects - a data driven description of a schema).


 - comfortable in Python, SQL not so much

 dont sell yourself short, you're moving rows and adding columns and that's a 
 fair degree of knowledge right there.

  - pull into the Postgres db from other sources
    - file system content
    - email
    - other db's: Mysql, rdf, ...
  - feed Sphinxsearch from the Postgres db

 for all of these you'd probably want to figure out some intermediary format 
 that everything goes into, then goes to the database.  Depending on how much 
 this format is hardwired to the SQL schema or not, as well as if you're 
 generally dealing with one big table to store a format versus many tables 
 storing a more normalized structure, would determine how well the ORM may or 
 may not be useful. The ORM is good when you have multiple tables in some 
 hierarchical structure that is to be related to an object hierarchy.   For a 
 straight up I'd like the columns in this Excel spreadsheet to become columns 
 in a new database table, it might be overkill.

I appreciate the advice, I'll be back.

Thanks,
Kent




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Re: [sqlalchemy] Newbie question

[Michael Bayer]

On Jul 28, 2011, at 11:47 AM, Kent Tenney wrote:

 
 It offers choices in that you can A. use core only or B. the ORM, as well 
 as choices in that it works with whatever kind of schema you'd like,
 
 I'll be studying doc for a better idea of the A/B distinction, as
 well as what kinds of schemas there are.
 
 I have the O'Reilly book, I understand SA has changed considerably
 since then, am I better off sticking with current doc?

Yes unfortunately the OReilly book, written against version 0.3 which was an 
early developmental stage for SQLAlchemy, will steer you more in the wrong 
direction today than anything, and we lack the resources to complete a new book 
which has been under contract for some time now.



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[sqlalchemy] Newbie question

[Kent Tenney]

Howdy,

I'm aggregating data from several Sqlite files into a Postgres db.
The sqlite files are storage for several apps I use: Shotwell,
Firefox, Zotero, Banshee ... I just watch and pull from them.

I've been using import sqlite3 so far, dumping sql from sqlite,
using it to create the Postgres tables. I then add columns to meet
my own needs. I now can diff 2 sqlite files, so I know what rows
need updating and adding in the Postgres tables.

I feel I should be using Sqlalchemy, but have been intimidated by
the wealth of choices SA offers. I don't want to start down the
wrong road.

However, as I look towards coding change merging, and
the new level of complexity it presents, I think it's time to
take the plunge.

Data specs:

- source data lives in other-owned files
- replicate source data tables in Postgres
- add columns to Postgres tables
- keep Postgres synced with sqlite sources

My proclivities:

- comfortable in Python, SQL not so much
- roadmap
  - pull into the Postgres db from other sources
- file system content
- email
- other db's: Mysql, rdf, ...
  - feed Sphinxsearch from the Postgres db

I would greatly appreciate any suggestions
on how to proceed.

Thanks,
Kent

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Re: [sqlalchemy] Newbie question

[Michael Bayer]

On Jul 27, 2011, at 3:21 PM, Kent Tenney wrote:

 Howdy,
 
 I'm aggregating data from several Sqlite files into a Postgres db.
 The sqlite files are storage for several apps I use: Shotwell,
 Firefox, Zotero, Banshee ... I just watch and pull from them.
 
 I've been using import sqlite3 so far, dumping sql from sqlite,
 using it to create the Postgres tables. I then add columns to meet
 my own needs. I now can diff 2 sqlite files, so I know what rows
 need updating and adding in the Postgres tables.
 
 I feel I should be using Sqlalchemy,

ok well what problems do you have currently that you'd like to solve ?


 but have been intimidated by
 the wealth of choices SA offers.

It offers choices in that you can A. use core only or B. the ORM, as well as 
choices in that it works with whatever kind of schema you'd like, which is 
the same choice you have anyway, and in this case it seems you have already 
made. Your app sounds like kind of a nuts and bolts table-to-table thing, 
i.e. is SQL centric, so using constructs like table.select() and table.insert() 
could perhaps reduce the verbosity of generating those statements by hand, the 
Table construct itself can turn the equation of what columns am i dealing with 
here? into a data driven one (the Table is a datastructure, which stores a 
list of Column objects - a data driven description of a schema).

 
 - comfortable in Python, SQL not so much

dont sell yourself short, you're moving rows and adding columns and that's a 
fair degree of knowledge right there.

  - pull into the Postgres db from other sources
- file system content
- email
- other db's: Mysql, rdf, ...
  - feed Sphinxsearch from the Postgres db

for all of these you'd probably want to figure out some intermediary format 
that everything goes into, then goes to the database.  Depending on how much 
this format is hardwired to the SQL schema or not, as well as if you're 
generally dealing with one big table to store a format versus many tables 
storing a more normalized structure, would determine how well the ORM may or 
may not be useful. The ORM is good when you have multiple tables in some 
hierarchical structure that is to be related to an object hierarchy.   For a 
straight up I'd like the columns in this Excel spreadsheet to become columns 
in a new database table, it might be overkill.



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[sqlalchemy] Newbie Question - Identity Mapper Issue

[koranthala]

Hi,
Does SqlAlchemy query call __init__ on the mapped object?

i.e. Say I have mapped the object to table as follows:
mapper(Obj, Table)
Now, table contains:
 index  integer
 x integer
 y integer

And Obj is defined as
Class Obj:
  def __init__(self, x, y):
 self.x = x
 self.y = y
 self.z = True

I have a query later:
 for query in session.query(Obj).order_by(Obj.index):
 --- print query.z
  This fails saying that z is not an element of query.

I was under the impression that query will return back initialized
objects with data updated with data from DB. But this doesnt seem to
be the case.
Could someone please help me out? Am I doing something wrong here?



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[sqlalchemy] Newbie question

[jrpfinch]

I have just started using Python and TurboGears with SQLAlchemy and I
think its great so far.  I am working with an already-created database
and am wondering what the best way is to represent the relationships
between the recurring_task and employee_status table:

employee_statuses = Table('employee_status', metadata,
#Column('emp_id', Integer, primary_key=True),
autoload=True)
recurring_tasks = Table('recurring_task', metadata,
#Column('rt_id', Integer, primary_key=True),
autoload=True)
class Employee_status(object):
pass
class Recurring_task(object):
pass
employee_status_mapper = mapper(Employee_status, employee_statuses)
recurring_task_mapper = mapper(Recurring_task, recurring_tasks)

So far, so good - this works in the tg-admin shell.  recurring_task
has three columns, rt_raiser, rt_owner and rt_status which are all
instances of employee_status.  I would be grateful if somebody could
indicate the best way to represent these relationships in the model as
I'm not sure which of the many examples in the documentation is
relevant - I am worried because I have one table referencing another
table multiple times.

Many thanks

Jon

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[sqlalchemy] Newbie question: sAsync maintained? In use?

[Dwig]

'm just getting started with SA, and I'll want to be using it in a
back-end server with an existing mssql database.  I'm considering
using Twisted as the basis for the server, and I've looked a bit into
using sAsync.  I've had trouble getting the Twisted XML-RPC Server
Example to run, and that led me to wonder about the status of the
package.

Is anyone here using sAsync, or knows enough to comment on its
viability for the kind of thing I've described.

Thanks for any good words,

--
Don Dwiggins
Advanced Publishing Technology

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[sqlalchemy] Newbie question: Too many connections

[mc]

Hi,
I keep getting The error: DBAPIError: (Connection failed)
(OperationalError) (1040, 'Too many connections').

At no time do I really need more than a few connections so I am doing
something basically wrong.
From reading the doc I concluded that pooling in the simple cases is
automatic. I must have misunderstood.

Questions:
1) What is the suggested method to debug such a problem? E.g. retrieve
the number of open connections.
2) When is a connection closed? For that matter , when is it open and
when taken from the pool?

TIA


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[sqlalchemy] Newbie question about transactions

[mc]

In the following code, I intended that nothing will be inserted into
the table because the transaction fails and is rolled back. What
actually happens is that the first insert is not rolled back because
it s committed by itself.
What is the correct way to achieve my goal?
TIA

from sqlalchemy import *
db=create_engine('mysql://user:pw@localhost/db')
cn= db.connect()
cn.execute(DROP TABLE IF EXISTS test)
cn.execute(CREATE TABLE test (`id` bigint(20) NOT NULL , PRIMARY KEY
(`id`))
 
ENGINE=InnoDB)
db.echo=True

md=BoundMetaData(db)
t=Table('test', md, autoload = True)

trans = cn.begin()
try:
insert(t).execute(id=332)
insert(t).execute(id=332)
trans.commit()
except:
trans.rollback()
raise


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[sqlalchemy] Newbie question about select statement

[Cristiano Paris]

I everyone. I'm pretty new to SQLAlchemy and never done much sql-related
work in the past as well so this could possibly be a silly question.

Suppose I've a table with a huge number of records. Now, I'd like to
access this table randomly through a list-like interface of a Python
class instance, i.e. saying foo[90] would return the 90th row of the table.

I know how to accomplish this in play MySQL's SQL, maybe using a LIMIT
clause in the select. This way it'd be trivial to write a container
class implementing the __getitem__() method with a a SELECT/LIMIT statement.

In addition, suppose that the SELECT statement contains a WHERE clause
defined at foo instance's creation time (possibly through its
constructor). Again, I'd simply plug the WHERE clause in the SELECT
statement on every __getitem()__ invocation.

I think it's be possible to implement such a beast through SQLAlchemy's
API and I thought that Query's select() method of a mapper worked that
way, but it seems that it fetches every and each row from the DB just
before returning a list of the mapped object instances.

Am I wrong? Is there a way/class in the SA's API to have sort of a lazy
list of results of a query from which to pick randomly?

Thank you,

Cristiano

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