A table is called a slave table when it "depends" on a master.
For example the BooksByAuthor table in Introduction to table views shows the books written by a given author. Or the ChoicesByQuestion table in The Lino Polls tutorial shows the choices for a given question (its master). Other examples of slave tables are used in A Local Exchange Trade System and Table summaries.
A slave table cannot render if we don't define the master. You cannot
ask Lino to render the
BooksByAuthor table if you don't
specify for which author you want it.
Slave tables are most often used as elements of a detail layout. In this case Lino renders them in a slave panel widget, and the current record is the master.
Slave tables with remote master¶
master_key of a slave table can be a remote
When you have three models A, B and C with A.b being a pointer to B and B.c being a pointer to C, then you can design a table CsByA which shows the C instances of a given A instance by saying:
class CsByA(Cs): master_key = "c__b"
lino_xl.lib.courses.ActivitiesByTopic shows all
courses about a given topic. But a course has no FK topic, so you
master_key = 'topic'. But a course does know its topic
indirectll because it knows it's course series, and the course series
knows its topic. So you can specify a remote field:
class ActivitiesByTopic(Courses): master_key = 'line__topic' allow_create = False
A slave table with a remote master should have
allow_create set to False because we cannot set a
line for a new course.