[storm] multiple join's

[Alex Richardson]

On Wed, Jan 14, 2009 at 3:56 PM, Gordon Allott <gordallott at gmail.com> wrote:
> Hi,
>
> I have a small problem understanding the join system in storm, If we
> take the join example in the tutorial,
> ( https://storm.canonical.com/Tutorial#Joins ) it involves a scenario
> where there is an Employee table and Company table, employee's reference
> companies and it suggest the following code to select companies that the
> employee 'Ben' belongs to:
> """
>>>> origin = [Company, Join(Employee, Employee.company_id ==
> Company.id)]
>>>> result = store.using(*origin).find(Company, Employee.name.like(u"Ben
> %"))
>
>>>> [company.name for company in result]
> [u'Sweets Inc.']
> """
>
> Which works great, but in my situation I would have to find more than
> one employee, for example, I may need to find the companies that 'Ben',
> 'Steve' and 'John' all belong to but am not quite sure how to go about
> doing that, just adding more clauses to the find query regarding the
> other employee's does not work.
>
> Thanks, Gord
> --
> Gordon Allott (gordallott at gmail.com)

Gordon,

There are two different topics that I think your posting touches on.

First is the question of who to use a join in a query. The tutorial
code you refer to properly demonstrates this. And it sounds like you
don't have any trouble getting the table join to work.

The second question is how to build a 'where' clause to select the
appropriate rows. In the simple example above, you could use the
following code to find the companies for Ben, Steve, and Jon:

origin = [Company, Join(Employee, Employee.company_id == Company.id)]
result = store.using(*origin).find(Company,
(Employee.name.like(u"Ben%") | (Employee.name.like(u"Ben%") |
(Employee.name.like(u"Ben%") ) )

Note that the pipe operator '|' is shorthand for the more
verbose/explicit use of the 'Or' method.

result = store.using(*origin).find(Company,
Or(Employee.name.like(u"Ben%"), (Employee.name.like(u"Ben%"),
(Employee.name.like(u"Ben%") ) )

The use of 'and', 'or' and 'in', to build more complex where clauses
is touched upon in the storm manual.
(https://storm.canonical.com/Manual)

Alex Richardson