Facts

A Jinaga data model is made of facts. A fact is an immutable JavaScript object which has a type field. Write a TypeScript or JavaScript class to help you create them. Here's an example in TypeScript.

export class Post {
  static Type = "Blog.Post" as const;
  public type = Post.Type;

  constructor(
    public createdAt: Date | string,
    public site: Site
  ) { }
}

See that Site type? That's another fact. That's how facts are related to each other.

Creating facts

Whenever the user does something, like create a blog post, your app creates a fact. Use the function j.fact to do that.

await j.fact(new Post(
  new Date(),
  site
));

Call the j.fact function within the browser or mobile app whenever you want to save something. It will be sent to the server, where it will be stored. You don't need a custom API.

Finding facts

To find a set of facts, first write a specification.

const postsInSite = model.given(Site).match((site, facts) =>
  facts.ofType(Post)
    .join(post => post.site, site)
    .select(post => ({
      hash: j.hash(post),
      titles: facts.ofType(PostTitle)
        .join(title => title.post, post)
        .select(title => title.value)
    }))
);

The specification finds all facts of a certain type related to the given starting point. It then selects the fields you want to use.

The query method returns all facts matching the specification.

const posts = await j.query(postsInSite, site);

Again, run this code in the browser or mobile client. There is no need to set up an API to perform this query on the server.

Displaying facts

A query is a one-time operation. If you want to update the UI every time a post is created, call the useSpecification hook.

const { loading, data, error } = useSpecification(j, postsInSite, site);

The data variable will contain the results of the query. Render the results in your component.

  return (
    <div>
      <h1>{site?.domain}</h1>
      { loading ? <p>Loading...</p> : null }
      { error ? <p>Error: {error.message}</p> : null }
      { data ? <ul>
        { data.map(post =>
          <li key={post.hash}>{post.titles.join(', ')}</li>
        ) }
      </ul> : null }
    </div>
  );

Subscribing to facts

To have new posts pushed to the browser or mobile app, call subscribe.

j.subscribe(postsInSite, site);

And with this, facts created by one user make their way to other users. You didn't write a custom API. You didn't set up a Web Socket listener. You didn't define a custom database schema.

Jinaga synchronizes immutable facts from client, to server, and back again. It persists them durably, transmits them reliably, and updates the view automatically.