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Build and run

In this topic, you'll build and deploy the Hello World dapp with the Chromia Command-line Interface (Chromia CLI). Read more about the features of the Chromia CLI in the Chromia CLI command reference section.

Prerequisites​

Run dapp in Chromia CLI​

Once you install the Chromia CLI, it's time to create a project.

  1. Create the project folder in a path of your choice and use the chr create-rell-dapp command.

    chr create-rell-dapp

    The chr create-rell-dapp command creates a new Rell structured project my-rell-dapp with the necessary files. A main.rell file, which includes the Hello World query and test files in the src/test/ folder. You also have a standard configuration for your project in the chromia. yml file. For more information, see the project config file.

    my-rell-dapp
       |--chromia.yml
       |--src
          |--main.rell
          |--test
             |--arithmetic_test.rell
             |--data_test.rell

    The next step is to start a node and run your app locally. You can do it in a couple of different ways, but the most straightforward method we recommend is the Chromia CLI.

  2. Start the node using the chr node start command inside the newly created project directory:

    cd my-rell-dapp
    chr node start

    The chr node start command starts a node with your applications running on it. All the blockchains listed in the blockchains key in the chromia.yml file get started.

    blockchains:
      my_rell_dapp: <----- This is the blockchain that starts
        module: main <----- This is the entry point of the chain

    The node should now be running with a local blockchain. The terminal where you ran chr node start will display info messages about committed blocks and transactions. Any print statements in your Rell code will also appear there.

    The last step is to query your dapp and test that the backend works correctly.

  3. Write the following in a new terminal with your project folder as the working directory. Remember to replace the <BlockchainRID> with your Blockchain RID from the node output.

    chr query hello_world
    note

    If your node is running on a URL other than the default http://localhost:7740, use the --api-url option with chr query.

  4. Your terminal should show you the following message.

    "Hello World!"

    Great! You've successfully queried your dapp. Queries are read-only operations that retrieve data from the blockchain.

  5. Now let's modify the data by running a transaction. Transactions (also called operations) can change the state of your dapp.

    First, generate a key pair to sign your transactions:

    chr keygen --key-id=chromia_key

    This creates a key pair in the .chromia folder (chromia_key and chromia_key.pubkey) that will be used to sign transactions.

  6. Run a transaction to change the name from "World" to "Developer":

    chr tx set_name "Developer"
    note

    If your node is running on a URL other than the default http://localhost:7740, use the --api-url option with chr tx.

  7. Query again to see the change:

    chr query hello_world

    Your terminal should now show:

    "Hello Developer!"

Great job! The Rell backend is up and running and works as it should. You've learned how to:

  • Query data from your dapp (read)
  • Run transactions to modify data (write)
  • Verify changes by querying again

You have now run a complete Hello World dapp in the Chromia CLI.

Optional Next steps​

Now that your Rell backend is running, you can: