Collections

Collections group similar data structures together and provide a friendly way of accessing and working with those data structures. Collections are very useful when used in conjuction with entities.

Entities are domain objects that are uniquely defined by a unique identifier.

In Engine, it's best to aim for achieving a balance between normalizing and denormalizing data based on the needs of observing changes or accessing partial or processed data. As a rule of thumb, data received from the outside of the system should be kept in a raw form somewhere so that it can be transformed in the many ways needed from your system.

Also, it's very important for an Entity to have its id stored in its data structure. Entities should always be able to exist on their own if needed.

In the following example several data processing patterns are used:

• articles.raw stores denormalized data received from an API.
• articles.items is created by a producer that reduces articles.raw and extracts only the information needed by the application; and only the items needed for the application.
• articles.ids is created by a producer that reduces articles.items and extracts only the list of ids. This is useful when you want to iterate on all articles but you don't want to get the data associated with the ids.
• articles.count is made by a producer that reduces articles.ids and gives the number of articles.
• articles.filters is made by a producer that groups articles by their category. It's useful when you want to iterate on a single category. The existence of this producer is determined by the need of this information.

{
  articles: {
    raw: {
      abc: {
        [...]
      },
      dfg: {
        [...]
      },
      xyz: {
        [...]
      },
    },
    items: {
      abc: {
        id: "abc",
        title: 'Abc shorts',
        category: 'shorts'
      },
      xyz: {
        id: "xyz",
        title: 'Xyz news',
        category: 'news'
      },
    },
    ids: ['xyz'],
    count: 1,
    filters: {
      category: {
        shorts: ['abc'],
        news: ['xyz]
      }
    },
  }
}