= Context =

A context is a way of defining a filter for a resource by it's links to another resource.

We access the filters via a common [wiki:S3/FieldSelectors FieldSelector] despite the back-end ther actual linkages varying from being as simple as a foreign key or going through a link table:
 * [wiki:S3/FieldSelectors#ContextPaths]

The context filters are usually defined in the core models ({{{modules/s3db/*.py}}}), like:
{{{
s3db.configure("project_project",
               context = {"location": "location.location_id",
                          "organisation": "organisation_id",
                          },
               )
}}}

This shows that:
* if we want "All Projects related to Organisation X" then the back-end will do this by using the simple Foreign Key 'organisation_id', although we can access that via {{{(organisation)}}}.
* if we want "All projects related to location Y" then the back-end will do this through the 'location' [wiki:S3/S3Model/ComponentResources Component], although we can access that via {{{(location)}}}.

Contexts get used a lot by [wiki:S3Profile Profile pages].