Repository: Repository Pattern

In R6P: Design Patterns in R

Repository Pattern

Description

Mediates between the domain and data mapping layers using a collection-like interface for accessing domain objects.

Super class

R6P::Singleton -> Repository

Methods

Public methods

• AbstractRepository$new()

• AbstractRepository$add()

• AbstractRepository$del()

• AbstractRepository$get()

---

Method new()

Instantiate an object

Usage

AbstractRepository$new()

---

Method add()

Add an element to the Repository.

Usage

AbstractRepository$add(key, value)

Arguments

key

(character) Name of the element.

value

(⁠?⁠) Value of the element. Note: The values in the Repository are not necessarily of the same type. That depends on the implementation of AbstractRepository.

---

Method del()

Delete an element from the Repository.

Usage

AbstractRepository$del(key)

Arguments

key

(character) Name of the element.

---

Method get()

Retrieve an element from the Repository.

Usage

AbstractRepository$get(key)

Arguments

key

(character) Name of the element.

Examples

# See more examples at <https://tidylab.github.io/R6P/articles>

# The following implementation is a Repository of car models with their
# specifications.

# First, we define the class constructor, initialize, to establish a
# transient data storage.

# In this case we use a dictionary from the collections package
# <https://randy3k.github.io/collections/reference/dict.html>

# Second, we define the add, del and get functions that operate on the dictionary.

# As an optional step, we define the NULL object. In this case, rather then
# the reserved word NULL, the NULL object is a data.frame with 0 rows and
# predefined column.

TransientRepository <- R6::R6Class(
  classname = "Repository", inherit = R6P::AbstractRepository, public = list(
    initialize = function() {
      private$cars <- collections::dict()
    },
    add = function(key, value) {
      private$cars$set(key, value)
      invisible(self)
    },
    del = function(key) {
      private$cars$remove(key)
      invisible(self)
    },
    get = function(key) {
      return(private$cars$get(key, default = private$NULL_car))
    }
  ), private = list(
    NULL_car = cbind(uid = NA_character_, datasets::mtcars)[0, ],
    cars = NULL
  )
)

# Adding customised operations is also possible via the R6 set function.
# The following example, adds a query that returns all the objects in the database

TransientRepository$set("public", "get_all_cars", overwrite = TRUE, function() {
  result <- private$cars$values() |> dplyr::bind_rows()
  if (nrow(result) == 0) {
    return(private$NULL_car)
  } else {
    return(result)
  }
})

# In this example, we use the mtcars dataset with a uid column that uniquely
# identifies the different cars in the Repository:
mtcars <- datasets::mtcars |> tibble::rownames_to_column("uid")
head(mtcars, 2)

# Here is how the caller uses the Repository:

## Instantiate a repository object
repository <- TransientRepository$new()

## Add two different cars specification to the repository
repository$add(key = "Mazda RX4", value = dplyr::filter(mtcars, uid == "Mazda RX4"))
repository$add(key = "Mazda RX4 Wag", value = dplyr::filter(mtcars, uid == "Mazda RX4 Wag"))

## Get "Mazda RX4" specification
repository$get(key = "Mazda RX4")

## Get all the specifications in the repository
repository$get_all_cars()

## Delete "Mazda RX4" specification
repository$del(key = "Mazda RX4")

## Get "Mazda RX4" specification
repository$get(key = "Mazda RX4")

R6P documentation built on April 12, 2025, 1:33 a.m.