dm_nest_tbl() converts a child table to a nested column in its parent
table.
The child table should not have children itself (i.e. it needs to be a
terminal child table).
Usage
dm_nest_tbl(dm, child_table, into = NULL)
Arguments
dm
A dm.
child_table
A terminal table with one parent table.
into
The table to nest child_tables into, optional as it can be guessed
from the foreign keys unambiguously but useful to be explicit.