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Version: v3.x (DDN)

Get Started with Hasura DDN and ClickHouse

Overview

This tutorial takes about fifteen minutes to complete. You'll learn how to:

  • Set up a new Hasura DDN project
  • Connect it to a ClickHouse instance
  • Generate Hasura metadata
  • Create a build
  • Run your first query

Additionally, we'll familiarize you with the steps and workflows necessary to iterate on your API.

This tutorial assumes you're starting from scratch. We'll use a locally running ClickHouse instance via Docker and connect it to Hasura, but you can easily follow the steps if you already have data seeded or are using ClickHouse's hosted service; Hasura will never modify your source schema.

Prerequisites

Install the DDN CLI

Simply run the installer script in your terminal:

curl -L https://graphql-engine-cdn.hasura.io/ddn/cli/v4/get.sh | bash

Install Docker

The Docker based workflow helps you iterate and develop locally without deploying any changes to Hasura DDN, making the development experience faster and your feedback loops shorter. You'll need Docker Compose v2.27.1 or later.

Validate the installation

You can verify that the DDN CLI is installed correctly by running:

ddn doctor

Tutorial

Step 1. Authenticate your CLI

Before you can create a new Hasura DDN project, you need to authenticate your CLI:
ddn auth login

This will launch a browser window prompting you to log in or sign up for Hasura DDN. After you log in, the CLI will acknowledge your login, giving you access to Hasura Cloud resources.

Step 2. Scaffold out a new local project

Next, create a new local project:
ddn supergraph init my-project && cd my-project

Once you move into this directory, you'll see your project scaffolded out for you. You can view the structure by either running ls in your terminal, or by opening the directory in your preferred editor.

Step 3. Initialize your ClickHouse connector

In your project directory, run:
ddn connector init my_ch -i

From the dropdown, start typing clickhouse and hit enter to accept the default port. Then, provide the following values:

Connection string

http://local.hasura.dev:8123

Username

default_user

Password

default_password

Step 4. Start the local ClickHouse container

Begin by creating a compose file for the ClickHouse service:
touch app/connector/my_ch/compose.clickhouse.yaml
Then, open the file and add the following:
services:
clickhouse:
image: clickhouse/clickhouse-server
container_name: clickhouse-server
ports:
- "8123:8123"
- "9000:9000"
volumes:
- ./clickhouse-data:/var/lib/clickhouse
environment:
CLICKHOUSE_USER: "default_user"
CLICKHOUSE_PASSWORD: "default_password"
CLICKHOUSE_DB: "default"
Run the container:
docker compose -f app/connector/my_ch/compose.clickhouse.yaml up -d
Send a curl request to create the table in the database:
curl -u default_user:default_password -X POST \
--data "CREATE TABLE users (user_id UInt32, name String, age UInt8) ENGINE = MergeTree() ORDER BY user_id;" \
http://localhost:8123
Then, seed the table:
curl -u default_user:default_password -X POST \
--data "INSERT INTO users (user_id, name, age) VALUES (1, 'Alice', 25), (2, 'Bob', 30), (3, 'Charlie', 35);" \
http://localhost:8123
You can verify this by running:
curl -u default_user:default_password -X POST \
--data "SELECT * FROM users;" \
http://localhost:8123

You should see a list of users returned.

Step 5. Introspect your ClickHouse database

Next, use the CLI to introspect your ClickHouse database:
ddn connector introspect my_ch

After running this, you should see a representation of your database's schema in the app/connector/my_ch/configuration.json file; you can view this using cat or open the file in your editor.

Additionally, you can check which resources are available — and their status — at any point using the CLI:
ddn connector show-resources my_ch

Step 6. Add your model

Now, track the table from your ClickHouse database as a model in your DDN metadata:
ddn models add my_ch users

Open the app/metadata directory and you'll find a newly-generated file: Users.hml. The DDN CLI will use this Hasura Metadata Language file to represent the users table from ClickHouse in your API as a model.

Step 7. Create a new build

To create a local build, run:
ddn supergraph build local

The build is stored as a set of JSON files in engine/build.

Step 8. Start your local services

Start your local Hasura DDN Engine and ClickHouse connector:
ddn run docker-start

Your terminal will be taken over by logs for the different services.

Step 9. Run your first query

In a new terminal tab, open your local console:
ddn console --local
In the GraphiQL explorer of the console, write this query:
query {
users {
userId
name
age
}
}
You'll get the following response:
{
"data": {
"users": [
{
"userId": 1,
"name": "Alice",
"age": 25
},
{
"userId": 2,
"name": "Bob",
"age": 30
},
{
"userId": 3,
"name": "Charlie",
"age": 35
}
]
}
}

Step 10. Iterate on your ClickHouse schema

Let's add a new table for posts:
curl -u default_user:default_password -X POST \
--data "CREATE TABLE posts (
user_id UInt32,
post_id UInt32,
title String,
content String
) ENGINE = MergeTree()
ORDER BY user_id;" \
http://localhost:8123
Then, seed it:
curl -u default_user:default_password -X POST \
--data "INSERT INTO posts (user_id, post_id, title, content) VALUES
(1, 1, 'My First Post', 'This is Alice''s first post.'),
(1, 2, 'Another Post', 'Alice writes again!'),
(2, 3, 'Bob''s Post', 'Bob shares his thoughts.'),
(3, 4, 'Hello World', 'Charlie joins the conversation.');" \
http://localhost:8123
Finally, we can check the posts were generated:
curl -u default_user:default_password -X POST \
--data "SELECT * FROM posts;" \
http://localhost:8123

Step 11. Refresh your metadata and rebuild your project

tip

The following steps are necessary each time you make changes to your source schema. This includes, adding, modifying, or dropping tables.

Step 11.1. Re-introspect your data source

Run the introspection command again:
ddn connector introspect my_ch

In app/connector/my_ch/configuration.json, you'll see schema updated to include operations for the posts table. In app/metadata/my_ch.hml, you'll see posts present in the metadata as well.

Step 11.2. Update your metadata

Add the posts model:
ddn model add my_ch posts

Step 11.3. Kill your services

Bring down the services by pressing CTRL+C in the terminal tab logging their activity.

Step 11.4. Create a new build

Next, create a new build:
ddn supergraph build local

Step 11.5 Restart your services

Bring everything back up:
ddn run docker-start

Step 12. Query your new build

Head back to your console and query the posts model:
query GetPosts {
posts {
userId
postId
title
content
}
}
You'll get a response like this:
{
"data": {
"posts": [
{
"userId": 1,
"postId": 1,
"title": "My First Post",
"content": "This is Alice's first post."
},
{
"userId": 1,
"postId": 2,
"title": "Another Post",
"content": "Alice writes again!"
},
{
"userId": 2,
"postId": 3,
"title": "Bob's Post",
"content": "Bob shares his thoughts."
},
{
"userId": 3,
"postId": 4,
"title": "Hello World",
"content": "Charlie joins the conversation."
}
]
}
}

Step 13. Create a relationship

Open the Posts.hml file and add the following to the end:
---
kind: Relationship
version: v1
definition:
name: user
sourceType: Posts
target:
model:
name: Users
relationshipType: Object
mapping:
- source:
fieldPath:
- fieldName: userId
target:
modelField:
- fieldName: userId
LSP-Assisted authoring is available

We've created an extension for VS Code that leverages LSP to make authoring these metadata objects easier. Check it out here.

Step 14. Rebuild your project

Bring down the services by pressing CTRL+C in the terminal tab logging their activity.

As your metadata has changed, create a new build:
ddn supergraph build local
Bring everything back up:
ddn run docker-start

Step 15. Query using your relationship

Now, execute a nested query using your relationship:
query GetPosts {
posts {
postId
title
content
user {
userId
name
age
}
}
}
Which should return a result like this:
{
"data": {
"posts": [
{
"postId": 1,
"title": "My First Post",
"content": "This is Alice's first post.",
"user": {
"userId": 1,
"name": "Alice",
"age": 25
}
},
{
"postId": 2,
"title": "Another Post",
"content": "Alice writes again!",
"user": {
"userId": 1,
"name": "Alice",
"age": 25
}
},
{
"postId": 3,
"title": "Bob's Post",
"content": "Bob shares his thoughts.",
"user": {
"userId": 2,
"name": "Bob",
"age": 30
}
},
{
"postId": 4,
"title": "Hello World",
"content": "Charlie joins the conversation.",
"user": {
"userId": 3,
"name": "Charlie",
"age": 35
}
}
]
}
}

Next steps

Congratulations on completing your first Hasura DDN project with ClickHouse! 🎉

Here's what you just accomplished:

  • You started with a fresh project and connected it to a local ClickHouse database.
  • You set up metadata to represent your tables and relationships, which acts as the blueprint for your API.
  • Then, you created a build — essentially compiling everything into a ready-to-use API — and successfully ran your first GraphQL queries to fetch data.
  • Along the way, you learned how to iterate on your schema and refresh your metadata to reflect changes.

Now, you're equipped to connect and expose your data, empowering you to iterate and scale with confidence. Great work!

Take a look at our ClickHouse docs to learn more about how to use Hasura DDN with ClickHouse. Or, if you're ready, get started with adding permissions to control access to your API.