[[TOC]]
= S3REST =

  - see also: [wiki:RESTController] and [wiki:S3XRC]
== S3RESTController ==

The S3RESTController class implements a generic RESTful interface for database resources in S3.

This class is instantiated as the global callable '''s3rest''' object, which will be used by the ''shn_rest_controller()'' wrapper function.

'''s3rest''' can be configured dynamically, and can easily be used to build RESTful controllers throughout the application.

Important: an s3rest instance is created per request and must not be stored or referenced by static objects to avoid memory leaks!

The default method handlers of '''s3rest''' (provided by the ''shn_rest_controller()'' wrapper) implement CRUD (create, read, update, delete) in all major representations, including the capabilities of [wiki:S3XRC S3XRC] to use in-line XSLT for export and import of XML and JSON formats.

[[Image(s3rest.png)]]

Instead of the web2py ''request'' object, '''s3rest''' uses the ''[#S3RESTRequest S3RESTRequest]'' class (described below) to represent the current REST request. Unlike web2py's request, the S3RESTRequest of the current call is not a global object, but gets passed as argument when calling REST method handlers.

=== REST Methods ===

It is critical to understand how RESTful requests work.

A RESTful request has two components:

  - the '''URL''' addresses the resource
  - the '''HTTP method''' determines the action to be taken with that resource, which is either:
    - GET, PUT, POST or DELETE

A resource in this terminology is either:

  - a database table or one or more records in that table
  - a combination of tables or records (so called "compound" or "joined" resources)
  - a function in the application related to one of the above resource types

''Functions'' as resources in RESTful requests are to be understood and addressed as "sub"-resources of their respective '''primary resource'''.

The finally executed response action depends on the HTTP/method and on the type of resource addressed by the URL, e.g.

  - if the method is "GET" and the resource addressed is a database table, then the response will be a list of the records in that table
  - if the method is "PUT" and the resource addressed is a record in a table, then the response will be an update of that record with the data from the request body

=== CRUD Method Handlers ===

The default method handlers for each of CRUD+S are implemented in models/01_crud.py:

  - shn_read(jr, **attr)
  - shn_list(jr, **attr)
  - shn_create(jr, **attr)
  - shn_update(jr, **attr)
  - shn_delete(jr, **attr)
  - shn_search(jr, **attr)
  - shn_options(jr, **attr)
  - import_xml(jr, **attr)
  - import_json(jr, **attr)

where ''jr'' is the current ''S3RESTRequest'', and ''**attr'' contains all further arguments passed to the REST controller.

You can override these defaults at any time by 
{{{
s3rest.set_handler(action, handler)
}}}
where:

  - '''action''' is the name of the action, i.e. one of 'read', 'list', 'create', 'update', 'delete', 'search', 'options', 'import_xml' or 'import_json'
  - '''handler''' is the handler function/lambda

=== Custom Methods ===

You can also add resource-specific custom methods by:
{{{
  s3xrc.model.set_method(module, resource, method, action)
}}}
where:

  - '''module''' is the module prefix of a resource
  - '''resource''' is the name of the resource (without prefix)
  - '''method''' is a string representing the name of the method (e.g. "search_simple")
  - '''action''' is the method handler function/lambda

The ''action'' method has to take the same arguments as the default handlers: ''jr'' (S3RESTRequest) and ''**attr''.

=== Pre- and Post-Hooks ===

You can hook in a '''preprocessing''' function into the REST controller (as response.s3.prep) which will be called ''after'' the controller has parsed the request, but ''before'' it gets actually executed - with the current S3RESTRequest as argument (which includes the primary resource record, if any).

This allows you to easily make changes to resource settings (e.g. access control, list fields etc.), or even to the REST controller configuration (e.g. custom methods) depending on the request type, its parameters or the addressed resource, without having to parse the web2py request manually. You can even bypass the execution of the request and thus hook in your own REST controller - with the advantage that you don't need to parse the request anymore.

'''NB: Hooks should be added at the top of your controller function, especially pre-processing hooks.'''

A simple example:

Original code fragment:
{{{
    if len(request.args) == 0:
        # List View - reduce fields to declutter
        table.message.readable = False
        table.categories.readable = False
        table.verified_details.readable = False
        table.actioned_details.readable = False

    response.s3.pagination = True #enable SSPag here!

    return shn_rest_controller(module, resource, listadd=False)
}}}

Using the pre-processor hook instead:
{{{
    def log_prep(jr):
        if jr.representation == "html" and \
           jr.method is None and \
           jr.component is None:
            # List View - reduce fields to declutter
            table.message.readable = False
            table.categories.readable = False
            table.verified_details.readable = False
            table.actioned_details.readable = False
        return True

    response.s3.prep = log_prep
    response.s3.pagination = True #enable SSPag here!

    return shn_rest_controller(module, resource, listadd=False)
}}}

The return value of the preprocessor function can simply be True, in which case the REST request will be executed as usual. Returning False would lead to a HTTP400 "Invalid Request" exception being raised.

The return value of the preprocessor function can also be a dict for more granular control - containing the following elements (all optional):

 - '''success''': boolean (default: True)
 - '''output''': dict (default: None)
 - '''bypass''': boolean (default: False)

If ''bypass'' is True, then the REST controller does not execute the request (the post-hook is executed, though). ''output'' must not be None in this case - it will be returned from the REST controller.

If ''success'' is False, and ''output'' is not None, then the REST controller does not execute the request, but just returns "output" (post-hook will ''not'' be executed in this case).

If ''success'' is False and ''output'' is None, a HTTP400 "Invalid Request" will be raised instead.

Examples:

In most cases, you will just return "True" - in some cases you might want to raise an error, e.g.:
{{{
    response.error = "This request cannot be executed"
    return dict(
        success=False,
        output=dict(title="My Pagetitle", item="Sorry, no data..."))
}}}

There is also a '''post-processing hook''' (response.s3.postp) that allows you to execute something directly after the REST request has been executed, but before the shn_rest_controller returns. The post-hook function will be called with the current S3RESTRequest and the output dict of its execution as arguments.

== S3RESTRequest ==

Important: S3RESTRequest instances are generated per request and must not be stored or referenced by static or global objects to avoid memory leaks!
=== Attributes of the S3RESTRequest ===

The following attributes are set during initialisation of an S3RESTRequest object, no further call is required.

==== Controller Attributes ====

||'''rc'''||the resource controller object (''S3XRC'')||
||'''request'''||the original web2py request (''Storage'')||
||'''session'''||the current session (''Storage'')||

==== Request Attributes ====

||'''representation'''||the current representation of this request (''string'', lowercase)||
||'''http'''||the HTTP method of this request (''string'', always uppercase!)||
||'''extension'''||the extension found in the original request (''string'', lowercase)||
||'''method'''||the method of the request if not HTTP (''string'', always lowercase)||
||'''custom_action'''||the custom method handler for the request (''function'' or ''lambda'')||

==== Primary Resource Attributes ====

||'''prefix'''||the prefix (=module name) of the requested resource (''string'')||
||'''name'''||the name of the requested resource, without prefix (''string'')||
||'''tablename'''||the name of the primary table (''string'')||
||'''table'''||the primary table (''Table'')||
||'''id'''||the ID of the primary record (''int'')||
||'''record'''||the primary record (''Row'')||

==== Component Resource Attributes ====

||'''component'''||the requested component, if any (''!ObjectComponent'')||
||'''pkey'''||the primary key of the Resource/Component join (''string'')||
||'''fkey'''||the foreign key of the Resource/Component join (''string'')||
||'''component_name'''||the name of the component without prefix (''string'')||
||'''component_id'''||the ID of the component record as of the request, if any (''int'')||
||'''multiple'''||Flag indicating that multiple component records are allowed (''boolean'')||

==== Error Indicators ====

||'''error'''||the last error message (''string'')||
||'''invalid'''||Flag indicating this request as invalid (''boolean'')||
||'''badmethod'''||Flag indicating a bad method error (''boolean'')||
||'''badrecord'''||Flag indicating a invalid record ID error (''boolean'')||
||'''badrequest'''||Flag indicating an unqualified request error (''boolean'')||

'''!ObjectComponent''' contains:
  - '''prefix''', '''name''', '''tablename''', '''table''' and '''attr''' of the component
  - '''attr''' contains:
    - '''multiple''' Multiple-flag
    - '''editable''', '''deletable''' and '''listadd'''
    - '''list_fields''', '''rss''', '''main''' and '''extra'''
    - '''onaccept''', '''onvalidation''', '''delete_onaccept''' and '''delete_onvalidation'''
  - methods: '''set_attr()''' and '''get_attr()'''

=== Methods of the S3RESTRequest ===

==== Magic URLs ====

'''here(representation=None)'''
  - returns the URL of the current request

'''there(representation=None)'''
  - returns the URL of a HTTP GET request for the same resource

'''same(representation=None)'''
  - returns the URL of the current request with the primary record ID replaced by the string literal '[id]'

'''other(method=None, record_id=None, representation=None)'''
  - returns the URL of a request with another method and record ID, but for the same resource

==== Other functions ====

'''target()'''
  - returns the target table of the current request as tuple of (prefix, name, table, tablename)

'''export_xml(permit=None, audit=None, template=None, filterby=None, pretty_print=False)'''
  - exports the requested resources as XML

'''export_json(permit=None, audit=None, template=None, filterby=None, pretty_print=False)'''
  - exports the requested resources as JSON

'''import_xml(tree, permit=None, audit=None, onvalidation=None, onaccept=None)'''
  - import the requested resources from the given !ElementTree

'''options_xml(pretty_print=False)'''
  - exports the options of a field (or all fields) in the resource as XML

'''options_json(pretty_print=False)'''
  - exports the options of a field (or all fields) in the resource as JSON

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DeveloperGuidelines