In tidylab/ddd: Build Applications that Match their Business Domain

source(file.path(usethis::proj_get(), "vignettes",  "_common.R"))
name <- "Order"
domain <- "Pizza Ordering"
commands <- "add_item_to_order"
queries <- "review_order"

path_proj <- tempfile("article-")
path_script <- file.path("R", filename$entity(name, domain))
path_test <- file.path("tests", "testthat", "test-" %+% filename$entity(name, domain))
fs::dir_create(path_proj)

What does add_entity do?

Given the Entity name, and its domain name, and optionally commands and queries methods,

When add_entity is called

command <- "add_entity(name = '" %+% name %+% 
    "', domain = '" %+% domain %+% 
    "', commands = '" %+% commands %+% 
    "', queries = '" %+% queries %+%
    "')"
withr::with_dir(path_proj, eval(parse(text=command)))

Then the function:

• Generates boilerplate code for the Entity and saves it at r path_script;
• Generates a unit-test for the Entity and saves it at r path_test; and
• Opens the files (only in interactive mode).

message("You don't need to remember the naming style for the different DDD components.
Instead, <code>ddd</code> takes care of naming style for all domain objects.
This way DDD file names, classes and functions are congruent with each other."
)

What are the main components of an Entity?

The boilerplate code for the r name Entity class produced by add_entity looks like this:

r path_script

Notice the three public methods created by add_entity:

1. initialize is a constructor for new entities.

   • By DDD definition, every Entity must have a unique id (uid) which distinguishes it from other Entities.

2. add_item_to_order is a command boilerplate. You'll need to:

   • Replace ... with explicit (if any) input arguments; and
   • Implement the method behaviour. Remember, command doesn't return data.

3. review_order is a query boilerplate. You'll need to:

   • Replace its content to retrieve data from the object
   • Remember, query does not change the state of the system.

The boilerplate code for the r name Entity unit-test produced by add_entity looks like this:

r path_test

tidylab/ddd documentation built on Jan. 6, 2021, 8:16 a.m.