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Disable elements of the user interface

Lino provides several methods to customize whether data is editable or not.

Disable individual fields

Sometimes you want to disable (make non-editable) individual fields of a form based on certain conditions. The conditions for disabling individual fields can be application specific and based e.g. on user roles or the values of certain other fields of the object being displayed.

For example, in Lino Così an invoice disables most fields when it has been registered. Here are two screenshots of a same invoice, once when the invoice’s state is “draft” and once when it is “registered”:

In Lino you define this behaviour by overriding the disabled_fields instance method on your model.

class lino.core.model.Model

disabled_fields(self, ar)

Return a set of field names that should be disabled (i.e. not editable) for this database object.

Here is a fictive example:

class MyModel(dd.Model):
    ...
    def disabled_fields(self, ar):
        s = super(MyModel, self).disabled_fields(ar)
        ...
        return set()

The Invoice model used in above screenshots does something like this:

class Invoice(dd.Model):
  ...
  def disabled_fields(self, ar):
      df = super(Invoice, self).disabled_fields(ar)
      if self.state == InvoiceStates.registered:
          df.add('subject')
          df.add('payment_term')
          ...
      return df

The decision which fields to disable may depend an the current user. Here is a fictive example of a model Case where only the author may change first and last name:

class Case(dd.Model):
  ...
  def disabled_fields(self, ar):
      df = super(Case, self).disabled_fields(ar)
      if self.author == ar.get_user():
          return df
      df.add('first_name')
      df.add('last_name')
      return df

You may want to override this method on the actor instead of per model. In that case it must be a classmethod with two arguments obj and ar:

@classmethod
def disabled_fields(cls, obj, ar):
    s = super(MyActor, cls).disabled_fields(obj, ar)
    ...
    return set()

Note that Lino calls the disabled_fields method only once per database row and request. The returned set is cached in memory.

Disable actions

You may also disable actions simply by adding their name to the set returned by disabled_fields. (The method name disabled_fields() is actually misleading, one day we might rename it to disabled_elements()).

Disable editing of a whole table

In some data windows you may want to disable editing functionality altogether.

For example lino.modlib.changes.Changes or lino.modlib.checkdata.Messages. You don’t want to modify them, nor delete them, not create new rows in these data windows. Not even when you are a site manager.

You do this by setting Actor.editable to False. This will remove editing functionality for everybody.

Disable editing of a whole table

In other cases you want to remove editing functionality only for certain user types. You do this by overriding the Actor.hide_editing() method. For example lino_xl.lib.products.Products says that ProductsUser can see products, but only ProductsStaff can edit them:

class Products(dd.Table):

  required_roles = dd.login_required(ProductsUser)

  @classmethod
  def hide_editing(cls, user_type):
      if user_type is not None:
          if not user_type.has_required_roles([ProductsStaff]):
              return True
      return super(Products, cls).hide_editing(user_type)

class lino.core.actors.Actor

editable

Whether a data window on this actor is editable.

The front end uses this information to generate optimized JS code for these actors.

When this is False, Lino won’t even call get_view_permission() for actions that are not readonly.

Set this explicitly to True or False to make the whole actor editable or not. Otherwise Lino will guess what you want during startup and set it to False if the actor is a Table and has a get_data_rows method (which usually means that it is a virtual table), otherwise to True.

This attribute is not inherited to subclasses.

How to remove the navigation buttons

TODO: This section does not yet reflect the new dd.Actor.default_record_id attribute (which automatically disables navigation).

In some data windows you may want to disable navigation functionality altogether by setting hide_navigator to True.

For example the lino.modlib.users.Users actor shows all user accounts and defines a detail layout to edit their data fields. But this table must of course be visible only to a site manager. In order to give normal users a chance to see and edit at least their own user settings, we have the lino.modlib.users.MySettings actor. It inherits from lino.modlib.users.Users, but instead of showing a list of them, it jumps directly to the detail window of the current user. So we set the default action to “detail”. And of course we don’t want the user to be able to navigate to their fellow users. So we disable navigation:

class MySettings(Users):
    hide_navigator = True
    allow_create = False
    allow_delete = False

    @classmethod
    def get_default_action(cls):
        return cls.detail_action

Or the lino.modlib.system.SiteConfig object (a database model for which there is always exactly one instance in a given database). To edit it, we use the following data table:

class SiteConfigs(dd.Table):

    model = 'system.SiteConfig'
    hide_navigator = True

    detail_layout = """
    default_build_method
    """

    @classmethod
    def get_default_action(cls):
        return cls.detail_action

Or a shopping cart is done like this:

class MyCart(My, Carts):
    hide_navigator = True

Actors with a modified toolbar

The hide_top_toolbar attribute changes the toolbar (1) to be at the bottom of the window instead of the top and (2) to have only actor-specific actions, i.e. no navigation buttons, no refresh button, no displayText area.

This attribute is used only with ExtJS front end. In React it is ignored. For example lino.modlib.system.SiteConfigs does this:

class SiteConfigs(dd.Table):
    hide_top_toolbar = True

(TODO: rename it to something else.)