On Wed, Feb 18, 2009 at 3:13 PM, May <adles...@gmail.com> wrote:
>
> Hello Karen,
>
> Yes, I seem confused here. I've been trying everything. The key is
> that this query works correctly in the postgres database to retrieve
> the institutionname (institution), using the contact id retrieved from
> Project:
>
> select DISTINCT Institution.institution
> from Contactintermed, Institution, Project
> where Contactintermed.contact_id=Project.contact_id
> and Contactintermed.institution_id=Institution.id
>
>
What do you mean by "works correctly"? You mean it retrieves exactly one
result? If so, that is an accident of the data you happen to have in your
DB, not anything guaranteed by the models you have defined. As you have
defined your models, any Contact might have multiple associated
Institutions, so asking how to come up with THE institution associated with
a Contact is futile. There isn't one, there is a list (accessible via the
Contact.contactintermed_set related manager) of 0, 1, or more. If you want
to print out all Institutions associated with a Contact, you can iterate
through that set for each contact in the template, something like (warning
-- untested syntax, I could be misremembering details):
{% for project in results %}
{{project.contact|safe}}
{% for ci in project.contact.contactintermed_set.all %}
{{ ci.institution }}
{% endfor %}
{% endfor %}
But there is nothing in your data models that guarantees the length of
contactintermed_set for a given Contact is going to be 1. If there is
something in the actual data model that guarantees that then your Django
model definitions aren't properly reflecting your real data model.
> In Python after I do a search by keyword in the view to get the
> "results", I cannot get the template to display the institution name
> (which I call institution). The query must first retrieve the Project
> records. From the project records I can then grab the contactid,
> which is then used in the Contactintermed table, which then goes to
> the Institution table to retrieve the institution name (institution).
> The "results" statement, doesn't seem to drill down through the
> Contactintermed table, even though I've tried adding the
> select_related to the statement.
select_related doesn't affect what's accessible via a model, it's purely a
performance optimization that affects how many SQL queries will be issued
under the covers when following ForeignKey relationships. It's also not
applicable here in terms of 'drilling down' to Contactintermed because
neither your Project nor your Contact model has a ForeignKey to
Contactintermed, rather Contactintermed is the one with the ForeignKeys back
to Contact and Institution.
Karen
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