dm_enum_fk_candidates: Foreign key candidates

In krlmlr/dm: Relational Data Models

Foreign key candidates

Description

Determine which columns would be good candidates to be used as foreign keys of a table, to reference the primary key column of another table of the dm object.

Usage

dm_enum_fk_candidates(dm, table, ref_table, ...)

enum_fk_candidates(dm_zoomed, ref_table, ...)

Arguments

dm	A dm object.
table	The table whose columns should be tested for suitability as foreign keys.
ref_table	A table with a primary key.
...	These dots are for future extensions and must be empty.
dm_zoomed	A dm with a zoomed table.

Details

dm_enum_fk_candidates() first checks if ref_table has a primary key set, if not, an error is thrown.

If ref_table does have a primary key, then a join operation will be tried using that key as the by argument of join() to match it to each column of table. Attempting to join incompatible columns triggers an error.

The outcome of the join operation determines the value of the why column in the result:

• an empty value for a column of table that is a suitable foreign key candidate

• the count and percentage of missing matches for a column that is not suitable

• the error message triggered for unsuitable candidates that may include the types of mismatched columns

enum_fk_candidates() works like dm_enum_fk_candidates() with the zoomed table as table.

Value

A tibble with the following columns:

columns

columns of table,

candidate

boolean: are these columns a candidate for a foreign key,

why

if not a candidate for a foreign key, explanation for for this.

Life cycle

These functions are marked "experimental" because we are not yet sure about the interface, in particular if we need both dm_enum...() and enum...() variants. Changing the interface later seems harmless because these functions are most likely used interactively.

See Also

Other foreign key functions: dm_add_fk(), dm_get_all_fks(), dm_rm_fk()

Examples

dm_nycflights13() %>%
  dm_enum_fk_candidates(flights, airports)

dm_nycflights13() %>%
  dm_zoom_to(flights) %>%
  enum_fk_candidates(airports)

krlmlr/dm documentation built on April 3, 2024, 10:52 a.m.