Enumerations

Sometimes you want to restrict the values that can be assigned to a property. For example, you might want to restrict the categories of a product to a set of predefined values. A product might be of category book, movie, music, or other. This is where enumerations come in.

Defining an enumeration

To define an enumeration, we start the same as we do for any other type, by using a level 3 heading (###) and then the name of the type.

### ProductCategory

BOOK = "book"
MOVIE = "movie"
MUSIC = "music"
OTHER = "other"

We are defining a key and value here, where the value is the actual value of the enumeration and the key is an identifier. This is required, because when we want to re-use the enumeration in a programming language, we need to be able to refer to it by a key. For instance, in python we can pass an enumeration via the following code:

from model import ProductCategory, Product

product = Product(
    name="Inception",
    category=ProductCategory.MOVIE
)

print(product)

{
    "name": "Inception",
    "category": "movie"
}

Similar to how we can use an object as a type for a property, we can also use an enumeration as a type for a property:

### Product

- name
  - type: string
- category
  - type: ProductCategory