S3XRC | S3 RESTful API | s3_rest_controller

s3_rest_controller

Introduction

The so-called REST Controller (function s3_rest_controller()) is a helper function to easily apply the RESTful API of the S3Resource class to your controller.

s3_rest_controller does:

• parse and execute the incoming HTTP request on the specified resource
• populate and hand-over view variables
• choose and set the response view template (response.view)

Using s3_rest_controller, a basic RESTful controller for the pr_image table can look like:

def image():

    """ RESTful CRUD controller """

    return s3_rest_controller("pr", "image")

This exposes all standard URLs and methods for this table, including:

• interactive create, read, update, delete and list views
• non-interactive data export/import (GET/POST/PUT/DELETE) in multiple formats

Basic Syntax

output = s3_rest_controller(prefix, resourcename)

• prefix is the application prefix of the resource
• resourcename is the name of the resource (without prefix)

• output contains the result of the request and can be returned from the controller as-is
  • in interactive view formats, this is a dict of view variables

Basic Options

All of the following options are set using:

s3xrc.model.configure(table, key=value)

where:

• table is the respective DB table
• key is the setting key
• value is the configuration value

You can specify multiple settings at once:

s3xrc.model.configure(table, key1=value1, key2=value2, ...)

configure overrides any settings that have been made for that table before (e.g. in the model), where only the specified keys are changed while all others are left untouched.

You can also delete a particular setting by:

s3xrc.model.clear_config(table, "key")

where "key" must be the respective key as string.

CRUD Options

You can define which of the CRUD functions are allowed for your resource. By default, they are all True.

  s3xrc.mode.configure(table, editable=True,             # Records can be updated
                              insertable=True,           # New records can be added
                              deletable=True,            # Records can be deleted
                              listadd=True)              # to have a add-record form in list view

Note:

• these settings are completely independent from the user's permission to perform the respective actions. If you have set insertable=False, then adding records to this table will be impossible even if the user has the permission to add records.
• in standard views, the add-form in list views is hidden and can be activated by clicking the respective "Add Record" button. If listadd=False, then the "Add Record" button will redirect to the create-form view instead.
• these settings do not effect non-interactive representations

Redirection

Default destination of the redirection after a create or update is the read view of the processed record, after a delete it is the list view of the respective table.

The redirection destination can be configured per DB table, using:

s3xrc.model.configure(table, create_next=url)

s3xrc.model.configure(table, update_next=url)

s3xrc.model.configure(table, delete_next=url)

where:

• table is the respective DB table
• url is the URL to redirect to

If, for create_next or update_next, url contains the string literal "[id]" (or its URL-encoded equivalent), then this literal is replaced by the ID of the updated/newly created record before redirection.

Note:

Redirection does not happen after non-interactive data imports!

Callbacks

For every DB table, you can define functions to be invoked upon certain CRUD events. Those "callbacks" can be:

• a single callable (function, lambda, callable object)
• a list of callables, which are invoked in list order
• a dict of callables, where the tablename is used as key to find the callable to be invoked
• a dict of lists of callables, where the tablename is used as key to find the list of callables to be executed in list order

The return value of the callables, if any, is ignored.

Important:

Callbacks are invoked in the same manner during non-interactive data imports, where usually multiple records will be processed in one and the same request. Therefore, any callbacks must not redirect!

Validation Callbacks

You can define extra form validation methods to be invoked after a create/update form has successfully passed the indivdual field validation, by using:

s3xrc.model.configure(table, create_onvalidation=callback)

s3xrc.model.configure(table, update_onvalidation=callback)

where:

• table is the respective DB table
• callable is the callback setting, see Callbacks

If either of create_onvalidation or update_onvalidation is not set, then the onvalidation setting is tried:

s3xrc.model.configure(table, onvalidation=callback)

This allows you to define a common onvalidation callback for both create and update.

Onvalidation callbacks are meant to allow additional form data validation (beyond individual field validators). The callback functions receive the form as first and only parameter, while their return values will be ignored.

Any validation errors are to be reported directly into the form as:

form.errors[fieldname] = error_msg

where:

• fieldname is the field containing the invalid value
• error_msg is the error message to be displayed in the form close to that field

If after the execution of the onvalidation callback any messages are found in form.errors, then no data are being imported and instead, the process will return to the input view with the messages displayed close to the respective form fields.

In non-interactive data imports, the error message will be added to the import tree as extra attribute of the invalid element. The XML importer will however process all records in the import tree in order to find all validation errors before reporting the invalid tree to the sender, and in case ignore_errors is used, all valid records will be imported in the first attempt.

On-accept Callbacks

You can define methods to be invoked after a record has been created/updated, by using:

s3xrc.model.configure(table, create_onaccept=callback)

s3xrc.model.configure(table, update_onaccept=callback)

where:

• table is the respective DB table
• callable is the callback setting, see Callbacks

If either of create_onaccept or update_onaccept is not set, then the onaccept setting is tried:

s3xrc.model.configure(table, onaccept=callback)

This allows you to define a common onaccept callback for both create and update.

The onaccept callbacks are meant to perform extra post-processing of the newly created/updated record (e.g. to update dependent records). The callback functions receive the respective record as first and only parameter, while their return value will be ignored.

On-Delete Callback

You can define methods to be invoked after a record has been deleted, by using:

s3xrc.model.configure(table, ondelete=callback)

where:

• table is the respective DB table
• callable is the callback setting, see Callbacks

The ondelete callbacks are meant to perform extra post-processing of the deleted record (e.g. to update dependent records). The callback functions receive the respective record as first and only parameter, while their return value will be ignored.

Note:

At the time when the callback is invoked, the record is already deleted from the database.

Pagination

The default pagination method is server-side (SSPag), meaning, in list views the client will receive only the first of the available rows, and then retrieve more rows as needed by subsequent Ajax calls.

In contrast to that, in client-side pagination (CSPag) mode all available rows of the list are retrieved and send to the client at once. For most tables, though, this will probably be a huge data set and take a long time to extract and transmit, while mostly being unnecessary when the user only needs to see the first 20 rows to find what he's looking for.

However, some tables may by their nature only contain one or few rows, and then server-side pagination is not needed (in fact, inefficient). In these cases, the respective controller can turn it off by:

response.s3.no_sspag=True

View Control

In web2py, the default view is chosen after the name of the controller, i.e. if the controller is person(), then the default view is person.html.

s3_rest_controller() modifies this schema in order to allow you to create method-specific views for the same controller.

Default View

The default view is chosen in a fallback cascade, which is:

1. <prefix>/<resource-name>_<component-name>_<method>.html
2. <prefix>/<resource-name>_<method>.html
3. <method>.html

where:

• prefix is the application prefix of the resource name (e.g. "pr")
• resource-name is the name of the resource (e.g. "person")
• component-name is the name of the component resource (e.g. "address", only if the request targets a component resource)
• method is one of:
  • display
  • list
  • list_create (to be deprecated)
  • create
  • update
  • delete
  • search

Example:

http://localhost:8000/eden/pr/person/create.html

is looking for one of pr/person_create.html, pr/create.html or finally create.html as default view.

If none of these is found, "default.html" serves as catch-all fallback.

Custom View

To choose a custom view, you can easily override the default setting after s3_rest_controller returns:

  output = s3_rest_controller(prefix, resourcename)

  response.view = "myview.html"

  return output

Additional View Variables

In interactive view formats, any additional named arguments in the s3_rest_controller argument list will be added to the view variables:

output = s3_rest_controller(prefix, resourcename, **attr)

• attr: additional view variables

• any callable argument will be invoked with the S3Request as first and only argument, and its return value will be added to the view variables
• any non-callable argument will be added to the view variables as-is
• any argument that gives None will remove this key from the view variables

A typical use-case is rheader:

def my_rheader(r):
  if r.interactive and r.component:
    # Code producing the rheader...
    return rheader
  else:
    return None

output = s3_rest_controller(prefix, name, rheader=my_rheader)

If my_rheader(r) gives something else than None, then this value is added as rheader to the view variables.

Advanced Options

Pre-Process

• coming soon...

Passing information between main controller & pre-processor

Scope normally means that these 2 sections can only talk to each other via globals or the Request object.

If you need to pass data between them, you can use this trick:

vars = {} # the surrounding dict
def prep(r, vars):
    vars.update(x=y) # the actual variable to pass is x
    return True

response.s3.prep = lambda r, vars=vars: prep(r, vars)

output = shn_rest_controller(module, resource)

x = vars.get(x, None)

An example usage is in controllers/gis.py for location()

Post-Process

Method Handlers

Custom Methods

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