# Set up your project · Relationships in Rell explained · Learn Chromia

> Make sure the following prerequisites are in place before you begin:

Source: https://chromia.com/learn/relationships-course/setup/

Relationships in Rell explainedLesson 6 of 6

1. [01Relationships in Rell explained](https://chromia.com/learn/relationships-course/introduction/)
2. [02Creating Records](https://chromia.com/learn/relationships-course/joins/)
3. [03Many-to-many relationships](https://chromia.com/learn/relationships-course/many-to-many/)
4. [04One-to-many relationships](https://chromia.com/learn/relationships-course/one-to-many/)
5. [05One-to-one relationship](https://chromia.com/learn/relationships-course/one-to-one/)
6. [06Set up your project](https://chromia.com/learn/relationships-course/setup/)

[Learn](https://chromia.com/learn/)[Relationships in Rell explained](https://chromia.com/learn/relationships-course/)

06 / 06

# Set up your project

Make sure the following prerequisites are in place before you begin:

Set up PostgreSQL database

## Set up PostgreSQL database

Rell needs PostgreSQL 16.3. You can use the IDE without a database, but you won't be able to run a node. A console or a remote postchain app doesn't need a database.

Rell expects these database settings by default:

* database: `postchain`
* user: `postchain`
* password: `postchain`

## Install

1. Install Homebrew by following the [Homebrew setup instructions](https://brew.sh/).
2. Install PostgreSQL:

   shell

   ```
   brew install postgresql@16
   brew services start postgresql@16
   createuser -s postgres
   ```
3. Create and configure the database:

   plsql

   ```nolines
   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;"
   ```

   note

   A "peer authentication failed" error means you need to switch the authentication method from `peer` to `md5`. Make this change in the `pg_hba.conf` file of your `psql` database.

1. Install PostgreSQL:

   bash

   ```nolines
   sudo apt install postgresql-16
   ```
2. Create and configure the database:

   bash

   ```nolines
   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;"
   ```

1. Install Docker by following the [Docker setup instructions](https://docs.docker.com/engine/install/).
2. Create and configure the database:

   dockerfile

   ```nolines
   docker run --name postgres -e POSTGRES_USER=postchain -e POSTGRES_PASSWORD=postchain -p 5432:5432 -d postgres:16.3-alpine3.20
   ```

   note

   The Alpine image of PostgreSQL is used here because its default collation settings are already correct. You can also set the collation explicitly with this environment variable:

   bash

   ```nolines
   POSTGRES_INITDB_ARGS="--lc-collate=C.UTF-8 --lc-ctype=C.UTF-8 --encoding=UTF-8"
   ```

1. Get the PostgreSQL installer from the [PostgreSQL download page](https://www.postgresql.org/download/windows/).
2. Run the installer, then add the PostgreSQL folder that holds the binaries to your environment variables. In the Command Prompt (CMD), run the command below. Check that the path points to your binaries and substitute the real version number for the `<version>` placeholder:

   shell

   ```nolines
   setx POSTGRESQL "C:\Program Files\PostgreSQL\<version>\bin"
   ```
3. Close and reopen the Command Prompt (CMD) so the new environment variables take effect. Then run these two commands, one after the other, to create and configure the database:

   plsql

   ```nolines
   psql -U postgres -c "CREATE DATABASE postchain WITH TEMPLATE = template0 LC_COLLATE = 'en_US.UTF-8' LC_CTYPE = 'en_US.UTF-8' ENCODING 'UTF-8';"
   psql -U postgres -c "CREATE ROLE postchain LOGIN ENCRYPTED PASSWORD 'postchain'; GRANT ALL ON DATABASE postchain TO postchain;"
   ```

   note

   On some Windows versions, you may hit permission errors or problems caused by a faulty PostgreSQL installation. In that case, install Docker and run PostgreSQL as a container instead.

Install Chromia CLI

## Install Chromia CLI

The steps below show how to install and update the [Chromia CLI](https://gitlab.com/chromaway/core-tools/chromia-cli).

## Prerequisite

You need the following before you start:

* **PostgreSQL database**: Follow [Set up PostgreSQL database](https://docs.chromia.com/get-started/installation/#set-up-postgresql-database).
* **RELL\_JAVA environment**: Chromia CLI runs on a Java runtime, version 21 or later. The package managers handle this for you, so no manual setup is needed. To choose a specific Java runtime for Chromia CLI, set the RELL\_JAVA environment variable to the location of a valid Java installation.

## Installation

Install Chromia CLI through a package manager, or download it from [Chromia CLI Packages](https://gitlab.com/chromaway/core-tools/chromia-cli/-/packages).

On macOS, install Chromia CLI (`chr`) as follows:

1. If you don't have Homebrew yet, install it:

   bash

   ```nolines
   /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
   ```
2. Register the Chromia repository with Homebrew:

   bash

   ```nolines
   brew tap chromia/core https://gitlab.com/chromaway/core-tools/homebrew-chromia.git
   ```
3. Install Chromia CLI:

   bash

   ```nolines
   brew install chromia/core/chr
   ```

   info

   To pin a particular Chromia CLI version, run:

   shell

   ```
   brew install chromia/core/chr@<version>
   brew unlink chr
   brew link chr@<version>
   ```

   To see which versions are available, run `brew search chr`.
4. Confirm the installation by printing the version:

   bash

   ```nolines
   chr --version
   ```

On Linux or WSL (Windows Subsystem for Linux), install Chromia CLI (`chr`) as follows:

1. Fetch the public key for Chromia's `apt-repo` and add it to your trusted keyrings:

   bash

   ```nolines
   curl -fsSL https://apt.chromia.com/chromia.gpg | sudo tee /usr/share/keyrings/chromia.gpg
   ```
2. Add the Chromia repository to your package sources:

   bash

   ```nolines
   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
   ```
3. Refresh your package sources:

   bash

   ```nolines
   sudo apt-get update
   ```

   info

   If `apt.chromia.com` was added on your system before Chromia CLI version `0.16.0`, run this command so the repository can be updated:

   bash

   ```nolines
   sudo apt-get --allow-releaseinfo-change update
   ```
4. After the update finishes, install Chromia CLI:

   bash

   ```nolines
   sudo apt-get install chr
   ```
5. Confirm the installation by printing the version:

   bash

   ```nolines
   chr --version
   ```

On Windows, install Chromia CLI (`chr`) with [Scoop](https://scoop.sh/) as follows:

1. If you don't have Scoop yet, open PowerShell as Administrator and run:

   powershell

   ```nolines
   iwr -useb get.scoop.sh | iex
   ```
2. Add the Chromia bucket to Scoop:

   powershell

   ```nolines
   scoop bucket add chromia https://gitlab.com/chromaway/core-tools/scoop-chromia/
   ```
3. Add the Java bucket to Scoop:

   powershell

   ```nolines
   scoop bucket add java
   ```

   Scoop needs this bucket to fetch openjdk21, which chromia-cli depends on during installation.
4. Install Chromia CLI:

   powershell

   ```nolines
   scoop install chr
   ```
5. Confirm the installation by printing the version:

   powershell

   ```nolines
   chr --version
   ```

## Updating Chromia CLI

Get the newest Chromia CLI from the [package registry](https://gitlab.com/chromaway/core-tools/chromia-cli/-/packages). If you installed it through a package manager, update it with the command for your platform:

shell

```nolines
brew update
brew upgrade chr
```

shell

```nolines
sudo apt-get update
sudo apt-get install chr
```

shell

```nolines
scoop update
scoop update chr
```

## Docker

With Docker, you can run a self-contained Linux container that already has Chromia CLI installed. You still need the [PostgreSQL database](https://docs.chromia.com/get-started/installation/#set-up-postgresql-database) set up.

The published images require Docker to be installed and configured on your host. For Windows, Mac, and Linux instructions, see [install Docker](https://docs.docker.com/get-docker/) in the Docker documentation.

### Start the Docker container with Chromia CLI pre-installed

To run the latest Chromia CLI, pass the CLI image name and `chr` to the `docker run` command:

shell

```nolines
docker run --rm -v $(pwd):/usr/app registry.gitlab.com/chromaway/core-tools/chromia-cli/chr:<latest version> chr
```

Windows Command Prompt Users

Windows Command Prompt (cmd) doesn't understand the `$(pwd)` syntax. Use one of these instead:

* **PowerShell**: `$(Get-Location)` or `$(pwd)`
* **Command Prompt**: `%CD%`

**Command Prompt example:**

cmd

```nolines
docker run --rm -v %CD%:/usr/app registry.gitlab.com/chromaway/core-tools/chromia-cli/chr:<latest version> chr
```

note

Set up your `chromia.yml` file for your platform:

* **Mac**: Set `database:host` to `host.docker.internal`.
* **Windows**: Set `database:host` to `host.docker.internal` (Docker Desktop). If the node still cannot reach your database, try `172.17.0.1`, the default Docker bridge address on Linux.
* **Linux**: Add the `--network=host` argument to your Docker commands.

Without these settings, Chromia CLI can't connect to the PostgreSQL instance.

For details on updating or removing the Docker image, see the [Docker CLI reference](https://docs.docker.com/engine/reference/commandline/docker/).

bash

```
#!/bin/bash

# Allocate a pseudo-TTY one when run in interactive mode
if [ -t 0 ] && [ -t 1 ] ; then TTY="--tty"; else TTY=""; fi

docker run \
  # Sets the network to host to not need to change the database hostname (linux only)
  --network=host \
  # Set timezone based on system settings (linux only)
  -e TZ=$(cat /etc/timezone) \
  # Sets process ownership to current user
  --user $(id -u):$(id -g) \
  --mount type=bind,source="/etc/passwd",target=/etc/passwd,readonly \
  --mount type=bind,source="/etc/group",target=/etc/group,readonly \
  # Configures ssh-agent (only needed if chr install is called on non-public repositores)
  -e SSH_AUTH_SOCK=$SSH_AUTH_SOCK \
  --volume "$SSH_AUTH_SOCK:$SSH_AUTH_SOCK" \
  --mount type=bind,source="${HOME}/.ssh",target=${HOME}/.ssh,readonly \
  --mount type=bind,source="${HOME}/.config/jgit",target=${HOME}/.config/jgit \
  # Mounts current folder into the container (Use `Get-Location` on PowerShell)
  --mount type=bind,source="$(pwd)",target=/usr/app \
  --interactive ${TTY} \
  --rm \
  registry.gitlab.com/chromaway/core-tools/chromia-cli/chr:${CHR_VERSION:-latest} chr "$@"
```

Windows Command Prompt Users

The bash script uses `$(pwd)`, which Windows Command Prompt doesn't support. On Windows:

* **PowerShell**: run the command unchanged; PowerShell also understands `$(pwd)`
* **Command Prompt**: Change `$(pwd)` to `%CD%` in the mount command

**Mount line for Command Prompt:**

cmd

```nolines
--mount type=bind,source="%CD%",target=/usr/app \
```

Start by creating your blockchain app project with the Chromia CLI.

shell

```nolines
chr create-rell-dapp my_library --template=plain
```

shell

```nolines
cd my_library
```

Running this command creates the core project files and configuration you need.

Then set up the `chromia.yml` file:

chromia.yml

```
blockchains:
  my_library:
    module: library_management
compile:
  rellVersion: 0.14.9
database:
  schema: schema_my_library
test:
  modules:
    - test
```

Written for this site from Chromia’s public course. Code samples are the course’s own.

[← Previous**One-to-one relationship**](https://chromia.com/learn/relationships-course/one-to-one/)[Course done →**Start building**](https://chromia.com/developers/#start)

On this page

* [Install](#install)
* [Prerequisite](#prerequisite)
* [Installation](#installation)
* [Updating Chromia CLI](#updating-chromia-cli)
* [Docker](#docker)