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Virtual tables

virtual table

A data view that is not connected to any database model.

Which means that you are responsible for defining that data.

The rows of a virtual table are defined by a method get_data_rows. In data tables this method has a default implementation based on the model attribute.

The columns of a virtual table must be defined using virtual fields.

Here is an example of a virtual table (taken from the lino_book.projects.vtables demo project):

from lino.api import dd

DATA = [
    ["Belgium", "Eupen", 17000],
    ["Belgium", "Liege", 400000],
    ["Belgium", "Raeren", 5000],
    ["Estonia", "Tallinn", 400000],
    ["Estonia", "Vigala", 1500],

class MyBase(dd.VirtualTable):

    def get_data_rows(cls, ar):
        return DATA

    def country(cls, row, ar):
        return row[0]

class Cities(MyBase):

    column_names = "country city"

    def city(cls, row, ar):
        return row[1]

class CitiesAndInhabitants(Cities):

    column_names = "country city population"

    def population(cls, row, ar):
        return row[2]

We can show this table in a shell session:

>>> from lino import startup
>>> startup('lino_book.projects.vtables.settings')
>>> from lino.api.doctest import *
>>> rt.show(vtables.Cities)
========= =========
 Country   City
--------- ---------
 Belgium   Eupen
 Belgium   Liege
 Belgium   Raeren
 Estonia   Tallinn
 Estonia   Vigala
========= =========
>>> rt.show(vtables.CitiesAndInhabitants)
========= ========= ============
 Country   City      Population
--------- --------- ------------
 Belgium   Eupen     17000
 Belgium   Liege     400000
 Belgium   Raeren    5000
 Estonia   Tallinn   400000
 Estonia   Vigala    1500
========= ========= ============

Usage examples of virtual tables in real applications: