V23 Test a target roundtrip

Use your current course session. Preparation and course runner · R script ↓

Optional deep dive. Enable only the options named in each block, after preparing its packages or services.

V23a Define a custom source

Goal: Understand R's S3 extension protocol.

Prerequisites: H01; extras.

Create an in-memory source with a declared read capability. Register methods with their generics without editing package files. R's S3 method system here is unrelated to Amazon S3 storage.

training_step(
  "V23a",
  {
    training_source <- structure(
      list(data = policies),
      class = "training_source"
    )
    dr_check_component.training_source <- function(x, ...) invisible(x)
    dr_read_source.training_source <- function(source, ...) source$data
    dr_inspect.training_source <- function(x, ...) {
      list(type = "training_source")
    }
    dr_capabilities.training_source <- function(x, ...) {
      dr_component_capabilities(read = TRUE)
    }
    for (generic in c(
      "dr_check_component",
      "dr_read_source",
      "dr_inspect",
      "dr_capabilities"
    )) {
      registerS3method(
        generic,
        "training_source",
        get(paste0(generic, ".training_source")),
        envir = asNamespace("dataraft.core")
      )
    }
    print(dr_inspect(training_source))
  },
  needs = c("H01"),
  enabled = training_options$extras,
  optional = TRUE
)

Expected result: A safe description without data contents.

Task: Should dr_inspect read the actual data?

V23b Use the custom source

Goal: Plug an adapter into an ordinary product.

Prerequisites: V23a; adapters.

A custom adapter should work through the same product and contract interface.

training_step(
  "V23b",
  {
    custom_product <- dr_product(
      "policies.custom",
      training_source,
      contract = policy_contract
    )
    print(dr_collect(dr_run(custom_product, write = FALSE)))
    print(dataraft.adapters::dr_test_adapter(
      training_source,
      expected = policies
    ))
  },
  needs = c("V23a"),
  packages = c("dataraft.adapters"),
  enabled = training_options$extras,
  optional = TRUE
)

Expected result: Six unchanged policy rows.

Task: Which new function did the product need to learn?

V23 Test a target roundtrip

Goal: Read back what was written.

Prerequisites: H04; adapters; extras.

The target test needs read_back and a contract. A successful write alone does not prove a correct roundtrip.

training_step(
  "V23",
  {
    conformance_path <- file.path(training_root, "adapter-conformance")
    conformance <- dataraft.adapters::dr_test_adapter(
      dataraft.adapters::dr_target_rds(conformance_path),
      data = policies,
      context = list(contract = policy_contract),
      read_back = function(output) {
        dr_read_source(dataraft.adapters::dr_source_rds(
          conformance_path,
          output$version
        ))
      }
    )
    print(conformance)
  },
  needs = c("H04"),
  packages = c("dataraft.adapters"),
  enabled = training_options$extras,
  optional = TRUE
)

Expected result: A comparison of written and reread values.

Task: What additional failure test would be useful?