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Implement the model in Rell

In Chromia, you define your blockchain model using a language called Rell. Let’s break down the Rell code that represents our model:

src/news_feed/model.rell
module;

entity user {
  mutable name;
  key id: byte_array;
}

entity follower {
  index user;
  index follower: user;
  key user, follower;
}

entity post {
  timestamp = op_context.last_block_time;
  index user;
  content: text;
}

User entity​

The user entity acts as a database table that contains two fields: name and id. You make the name mutable, allowing users to change it, and mark id as a key to signify that it serves as the primary key, which must be unique. Here are some additional details:

  • name corresponds to the text datatype.

Follower entity​

The follower entity links one user to another as a follower. Let's break it down:

  • index user;: This field links to the user entity and creates a one-to-many relationship since a user can have multiple followers. By indexing this field, you enhance the speed of SQL queries.
  • index follower: user;: The second field, named "follower," represents the user who follows the specified user in the first field. You also index this field for efficient querying.
  • key user, follower;: This combined key ensures that each user can follow another user only once, maintaining the uniqueness of the follower relationship.

For a deeper understanding of managing relationships between entities, check out our Understand relationships in Rell course.

Post entity​

The post entity represents an actual post on your social media platform. It includes:

  • timestamp = op_context.last_block_time;: This field captures the timestamp with an implicit integer data type, defaulting to the time of the last known block's creation. This setup removes the need for you to set the timestamp explicitly in your code.
  • index user;: This field references the user who creates the post and is indexed for efficient retrieval.
  • content: text;: The content field stores the text content of the post.

Great! With Rell, you've established a basic database model for a social media platform on the Chromia blockchain. This model effectively stores user information, posts, and follower relationships. Now, you are ready to build your decentralized app on Chromia!