A Basic Example

We’re going to create a simple social network where users can follow each other and create posts.

You should create a python file called social_network.py, and a folder called helixdb-cfg with a query helix file called queries.hx, and a schema helix file called schema.hx.

The helix queries go in helixdb-cfg/queries.hx and the python code goes in social_network.py.

Step 0: Import HelixDB

import helix
from helix.client import Query
from helix.types import Payload
from typing import List
 
db = helix.Client(local=True)

Step 1: Define the schema in schema.hx

We’re going to define the schema for our social network in schema.hx. We’re going to have User nodes where users can Follow other users. We’re also going to have Post nodes where users can Create posts.

N::User {
    name: String,
    age: U32,
    email: String,
    created_at: I32,
    updated_at: I32,
}

N::Post {
    content: String,
    created_at: I32,
    updated_at: I32,
}

E::Follows {
    From: User,
    To: User,
    Properties: {
        since: I32,
    }
}

E::Created {
    From: User,
    To: Post,
    Properties: {
        created_at: I32,
    }
}

Step 2: Inserting data

Creating a user is done by inserting a new node into the graph.

QUERY create_user(name: String, age: U32, email: String, now: I32) =>
    user <- AddN<User>({name: name, age: age, email: email, created_at: now, updated_at: now})
    RETURN user

To let users follow another user, we need to create an edge between them.

QUERY create_follow(follower_id: ID, followed_id: ID, now: I32) =>
    follower <- N<User>(follower_id)
    followed <- N<User>(followed_id)
    AddE<Follows>({since: now})::From(follower)::To(followed)
    RETURN "success"

To create a post, we need to create a post node and an edge between the user and the post.

QUERY create_post(user_id: ID, content: String, now: I32) =>
    user <- N<User>(user_id)
    post <- AddN<Post>({content: content, created_at: now, updated_at: now})
    AddE<Created>({created_at: now})::From(user)::To(post)
    RETURN post

Step 3: Query the data

To get all users, we can use the following query:

QUERY get_users() =>
    users <- N<User>
    RETURN users

To get all posts, we can use the following query:

QUERY get_posts() =>
    posts <- N<Post>
    RETURN posts

To get all posts by a user, we can use the following query:

QUERY get_posts_by_user(user_id: ID) =>
    posts <- N<User>(user_id)::Out<Created>
    RETURN posts

To get all users that a user follows, we can use the following query:

QUERY get_followed_users(user_id: ID) =>
    followed <- N<User>(user_id)::Out<Follows>
    RETURN followed

As a more complex example, we could have a query that loads a page containing the posts of users that a user follows. To do this we are going to remap the posts to have a field containing information about the user that created the post.

QUERY get_followed_users_posts(user_id: ID) =>
    followers <- N<User>(user_id)::Out<Follows>
    posts <- followers::Out<Created>::RANGE(0, 40)
    RETURN posts::{
        post: content,
        creatorID: _::In<Created>::ID,
    }

A Basic Example

Step 0: Import HelixDB

Step 1: Define the schema in schema.hx

Step 2: Inserting data

Step 3: Query the data

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