Zero to a running dapp in 10 minutes

1Install the Chromia CLI2 min

curl -fsSL https://apt.chromia.com/chromia.gpg | sudo tee /usr/share/keyrings/chromia.gpg >/dev/null
echo "deb [arch=amd64 signed-by=/usr/share/keyrings/chromia.gpg] https://apt.chromia.com stable main" | sudo tee /etc/apt/sources.list.d/chromia.list
sudo apt-get update
sudo apt-get install chr

brew tap chromia/core https://gitlab.com/chromaway/core-tools/homebrew-chromia.git
brew install chromia/core/chr

Check it worked:

chr --version

chr version 0.34.3
rell version 0.16.7
postchain version 3.49.21
EIF version 0.32.7
Java version 21.0.13

2Set up PostgreSQL2 min

Rell stores your dapp’s data in PostgreSQL. Create the database and user the CLI expects by default (postchain / postchain).

sudo apt-get install postgresql
sudo service postgresql start
sudo -u postgres psql -c "CREATE DATABASE postchain WITH TEMPLATE = template0 LC_COLLATE = 'C.UTF-8' LC_CTYPE = 'C.UTF-8' ENCODING 'UTF-8';" -c "CREATE ROLE postchain LOGIN ENCRYPTED PASSWORD 'postchain'; GRANT ALL ON DATABASE postchain TO postchain;"

brew install postgresql@16
brew services start postgresql@16
export PATH="$(brew --prefix postgresql@16)/bin:$PATH"
createuser -s postgres
psql -U postgres -c "CREATE DATABASE postchain WITH TEMPLATE = template0 LC_COLLATE = 'C.UTF-8' LC_CTYPE = 'C.UTF-8' ENCODING 'UTF-8';" -c "CREATE ROLE postchain LOGIN ENCRYPTED PASSWORD 'postchain'; GRANT ALL ON DATABASE postchain TO postchain;"

3Create a dapp1 min

chr create-rell-dapp
cd my-rell-dapp

You get a working project: the dapp in src/main.rell, its tests in src/test/, and the project config in chromia.yml.

my-rell-dapp/
├── chromia.yml
├── src/
│   ├── main.rell
│   └── test/
│       ├── arithmetic_test.rell
│       └── data_test.rell
├── .rell_format
└── .rell_lint

The whole dapp is eleven lines:

module;

object my_name {
    mutable name = "World";
}

operation set_name(name) {
    my_name.name = name;
}

query hello_world() = "Hello %s!".format(my_name.name);

• object my_name is a single row stored on chain, starting as "World".
• operation set_name changes state. It runs inside a transaction.
• query hello_world reads state. Queries don’t change anything.

4Run the tests1 min

chr test

====================Running unit tests====================
TEST: test.arithmetic_test:test_foo
OK: test.arithmetic_test:test_foo (0.806s)
TEST: test.arithmetic_test:test_bar
OK: test.arithmetic_test:test_bar (0.458s)
TEST: test.data_test:test_add_name
OK: test.data_test:test_add_name (1.233s)
…
SUMMARY: 0 FAILED / 3 PASSED / 3 TOTAL (2.498s)

***** OK *****

Tests run against your local PostgreSQL. If this passes, Java, the CLI and the database are all set up correctly.

5Start a local node1 min

This starts a single-node Chromia blockchain on your machine and deploys your dapp to it. Leave it running and open a second terminal in my-rell-dapp for the next steps.

chr node start --wipe

Starting node with pubkey: 0324653EAC434488002CC06BBFB7F10FE18991E35F9FE4302DBEA6D2353DC0AB1C
Building Blockchain: my_rell_dapp
Started blockchain my_rell_dapp. Chain-id: 0, brid F6438317F85A756AE5E41485AF846D1D4F27EB1F8BE5FA2B6E27553AC558F091
Node is initialized

--wipe starts the chain from block 0. The node’s REST API listens on http://localhost:7740, which is where the next commands go.

6Query your dapp10 s

chr query hello_world

"Hello World!"

7Send a transaction1 min

chr tx set_name Alice --await

transaction with rid B28ECA83E1BFBDE7C63EE67D1957970D014882C0C49AE8A63644C126C94C222E was posted and confirmed

--await waits until the transaction is in a block. Now query again:

chr query hello_world

"Hello Alice!"

That’s a dapp running on a blockchain: state in a relational database, changed only by transactions, read with queries.

8Change the code and redeploy2 min

Add a query to the end of src/main.rell:

query greeting_length() = my_name.name.size();

Push the new code to the running node:

chr node update

Building Blockchain: my_rell_dapp
Configuration added at height 3

chr tx set_name Bob --await
chr query greeting_length

transaction with rid 717673BD82A69BEFDC7095247B6C2A18D8104E6944C1EF099FC58B73295D0F71 was posted and confirmed
3

Stop the node with Ctrl+C in its terminal when you’re done.

9Deploy to Testnet15 min

Commands and flags checked against chr 0.34.3 · not deployed in this test

Your dapp works locally. To put it on the public Testnet you need test tokens (tCHR) and a leased container. The full walkthrough is on Deploy to Testnet; the short version, from the same project folder:

chr keygen --key-id testnet_container_key
# lease a container at vault.testnet.chromia.com/containers with the printed pubkey,
# add the deployments block to chromia.yml, then:
chr deployment create --network testnet --key-id testnet_container_key