Custom Data Provider

Kotlin-faker allows you to easily create your own custom fake data generators (providers), and even new fakers.

Let's assume you want to create a FooBar data generator with support for the default en locale.

First, we need to create a json file that will serve as your "data dictionary", e.g. resources/locales/en/foobar.json, with the following contents:

{
  "en": {
    "faker": {
      "custom": {
        "foobar": {
          "foo": ["foo", "bar", "baz"],
          "bar": "foobar",
          "baz": "### ???"
        }
      }
    }
  }
}

• The first key in the json file should match the locale name.
• The second key should always be faker and the third custom
• The next key, foobar in this case, can be anything you want.
  • For en locale, the json filename should either match this key, or should be custom.json.
  • If the filename is foobar.json, we need to override the secondaryCategory property in the data generator implementation (see ❷ below), and pass this property as second argument to fakerService.load (see ❸ below).
• After that you have your data parameters with values as key-value pairs

Then, we need to implement the YamlFakeDataProvider class:

class FooBar(fakerService: FakerService) : YamlFakeDataProvider<FooBar>(fakerService) {
    override val yamlCategory: YamlCategory = YamlCategory.CUSTOM // ❶
    override val secondaryCategory: Category = Category.ofName("FOOBAR") // ❷
    override val localUniqueDataProvider = LocalUniqueDataProvider<FooBar>()
    override val unique: FooBar by UniqueProviderDelegate(localUniqueDataProvider, fakerService)

    init {
        fakerService.load(yamlCategory, secondaryCategory) // ❸
    }

    fun foo(): String = resolve(secondaryCategory, "foo")
    fun bar(): String = resolve(secondaryCategory, "bar")
    fun baz(): String = with(fakerService) { resolve(secondaryCategory, "baz").numerify().letterify() } // ❹
}

❶ The yamlCategory should generally use YamlCategory.CUSTOM enum class. Although you could also use one of the existing categories if you like, one should be careful not to override existing functionality in a given data provider. ❷ If our json file is named foobar.json, the secondaryKey needs to override the category name ❸ In this case we also need to pass the secondaryCategory argument to fakerService.load function ❹ You have access to all default faker functionality, i.e. FakerService#numerify to replace all # placeholders with a random digit, and FakerService#letterify to replace all ? with a random letter

Last, we need to add a very simple implementation of the AbstractFaker:

class CustomFaker(config: FakerConfig = fakerConfig { }) : AbstractFaker(config) {

    val fooBar by lazy { FooBar(fakerService) }
}

From there we can use our CustomFaker just like any other:

val testFaker = CustomFaker()
println(testFaker.fooBar.foo()) // baz
println(testFaker.fooBar.bar()) // foobar
println(testFaker.fooBar.baz()) // ABC 123