= S3ResourceFilter =

S3ResourceFilter is a class representing the DAL queries and Python filters to select the records for a resource.

== Overview ==

S3ResourceFilters are a part of S3Resources:

[[Image(rfilter.png)]]

They contain the queries and filters to extract the data from the database.

At the time an S3Resource gets defined, a S3ResourceFilter is automatically added to it. This default filter (so called "master query") covers:

  - available records (i.e. not deleted)
  - accessible records (i.e. access permitted)
  - selected records by record ID and/or UID
  - joined records (e.g. components)

It is possible to extend this filter during the request:

  - by a URL query
  - by the {{{S3Resource.add_filter()}}} method

S3ResourceFilters can filter for both real fields in the database table as well as virtual (computed) fields.

== Design ==

S3ResourceFilters consist of a hierarchical set of web2py Query and S3ResourceQuery objects, where:

  - Query instances represent the DAL queries ("query")
  - S3ResourceQuery instances represent virtual field filters ("vfltr")

The process for the extraction of rows from the database is as follows: