#' @description

## Usage

dm_unpack_tbl(dm, child_table, col, ptype)

## Arguments

dm

A dm.

child_table

A table in the dm with packed columns.

col

The column to unpack (unquoted).

ptype

A dm, only used to query names of primary and foreign keys.

## Details

dm_unpack_tbl() targets a specific column to unpack from the given table in a given dm. A ptype or a set of keys should be given, not both.

dm_pack_tbl() is an inverse operation to dm_unpack_tbl() if differences in row and column order are ignored. The opposite is true if referential constraints between both tables are satisfied and if all rows in the parent table have at least one child row, i.e. if the relationship is of cardinality 1:n or 1:1.

dm_unwrap_tbl(), dm_unnest_tbl(), dm_nest_tbl(), dm_pack_tbl(), dm_wrap_tbl(), dm_examine_constraints(), dm_examine_cardinalities(), dm_ptype().

## Examples

flights_wrapped <-
dm_nycflights13() %>%
dm_wrap_tbl(flights)

# The ptype is required for reconstruction.
# It can be an empty dm, only primary and foreign keys are considered.
ptype <- dm_ptype(dm_nycflights13())

flights_wrapped %>%
dm_unpack_tbl(flights, airlines, ptype)
#> Tables: flights, airlines