Introduction to actions

This section tries to explain everything you need to know about actions.

Overview

An action is a Python class that describes "something that an end user might want to do". Actions are rendered as menu items, toolbar buttons or simply clickable text in arbitrary places.

A series of standard actions gets installed more or less automatically on every actor when Lino starts up. For example DeleteRow, ShowInsert, TableInsert. They are defined in lino.core.actions.

As an application developer you can define new Writing custom actions, or also override standard actions with your own custom actions.

Some action attributes include:

class lino.core.actions.Action
label

The text to place on the button or menu item. A short descriptive text in user language. Used e.g. on menu items. Also on toolbar buttons if they have neither icon_name nor button_text.

button_text = None

The text to appear on buttons for this action. If this is not defined, the label is used.

required_roles

Permission requirements to specify for whom and under which conditions this action is available.

See lino.core.permissions.Permittable.required_roles.

help_text

The text to appear as tooltip when the mouse is over that button.

A help text that shortly explains what this action does. In a graphical user interface this will be rendered as a tooltip text.

If this is not given by the code, Lino will potentially set it at startup when loading the help_texts.py files.

Every custom action has handler function : which will be called when the action is invoked.

Actions are always linked to a given actor. Each actor has a list of actions that it "offers".

bound action

An action that is bound to its actor.

Some standard actions

class lino.core.actions.ShowTable

Open a window with a tabular grid editor on this table. The grid editor is that main widget of that window (otherwise it would be a slave table).

Most items of the main menu are ShowTable actions.

class lino.core.actions.ShowDetail

Open the detail window on a table actor.

class lino.core.actions.ShowInsert

Open an insert window on this actor. A new row will be inserted only when this window gets submitted, which is a separate action named SubmitInsert.

class lino.core.actions.SubmitInsert

Create a new database row using the data specified in the insert window. Called when the Create button of an insert window was clicked.

Most database models share the same action instance of this, which is stored in the submit_insert class attribute.

Window actions

Some actions do nothing but opening a new window on the client. We call them window actions.

Examples of window actions are ShowTable, ShowDetail and ShowInsert.

This behaviour is specified by the opens_a_window attribute.

Action.opens_a_window

Specifies whether this action opens a window. It is up to the front end to actually render that window.

Another class of actions also open a window, but that window is not their main purpose. For example the Merge action always opens a dialog window with miscellaneous parameters, and the action itself will execute only when the user confirms that dialog window. These actions are called parameter actions.

Or the DeleteSelected action is visible in the toolbars of the grid and the detail windows and in the context menu on a grid row.

Read-only actions

Action.readonly

A read-only action is an action that doesn't cause any change in the current data object. A read-only action has its readonly attribute set to True.

For example the lino.modlib.printing.DirectPrintAction action is read-only. Also ShowInsert is read-only because it does not modify the current data object. Otherwise it would be disabled on a registered invoice.

Setting readonly to False will (1) disable the action for readonly user types or when lino.core.site.Site.readonly is True, and (2) will cause it to be logged when log_each_action_request is set to True.

Note that when a read-only action actually does modify the object, Lino won't "notice" it.

Discussion

Maybe we should change the name readonly to modifying or writing (and set the default value False). Because that would look more intuitive for the application developer. Or --maybe better but probably with even more consequences-- the default value should be False. Because being read-only, for actions, is a kind of "privilege": they don't get logged, they also exist for read-only users... It would be more "secure" when the developer must explicitly "say something" in order to grant that privilege.

Another subtlety is the fact that this attribute is used by lino.modlib.users.UserAuthored. For example the StartTicketSession action in Lino Noi is declared readonly because we want Workers who are not Triagers to see this action even if they are not the author (reporter) of a ticket. In this use case the attribute name should rather be requires_authorship.

Action instances

A same action instance can be shared by many actors. For example the DeleteSelected action exists only as one instance shared among all actors that use it.

Other actions can exist as different instances even on a same actor. For example the lino.modlib.printing.DirectPrintAction.

Instance actions

instance action

An action that has been bound to a given database object.

An instance action exists only as long as the Python representation of the database object exists.

The default action of an actor

Each actor has a default action. The default action for table views is ShowTable. That's why you can define a menu item by simply naming the table view.

For example in the setup_menu method in the Polls tutorial) we say:

def setup_menu(self, user_type, main):
    super(Site, self).setup_menu(user_type, main)
    m = main.add_menu("polls", "Polls")
    m.add_action('polls.Questions')
    m.add_action('polls.Choices')

(Above snippet is from lino_book/projects/polls/mysite/settings.py)

The add_action method of Lino's lino.core.menus.Menu is smart enough to understand that if you specify a Table, you mean in fact that table's default action.