# Adapter: H2

The H2 adapter was contributed by community member [clang-engineer](https://github.com/clang-engineer).

See the [harlequin-h2 repository](https://github.com/clang-engineer/harlequin-h2) for the most up-to-date documentation.

## Installation

Install the adapter into the same environment as Harlequin:

```bash
uv tool install harlequin --with harlequin-h2
```

The adapter requires a Java runtime compatible with your H2 version and an H2 2.x JDBC driver JAR. If the adapter does not discover the JAR automatically, provide its path with `--jar` or the `H2_JAR` environment variable.

## Usage

Select the adapter with `-a h2` and pass an H2 JDBC URL.

### Embedded file database

```bash
harlequin -a h2 -U sa \
  "jdbc:h2:file:/path/to/database;AUTO_SERVER=TRUE;IFEXISTS=TRUE"
```

`AUTO_SERVER=TRUE` allows Harlequin and another JVM process to share the file. `IFEXISTS=TRUE` prevents a mistyped path from creating a new empty database.

### Embedded memory database

```bash
harlequin -a h2 "jdbc:h2:mem:demo"
```

The named database normally exists until its last connection closes. Add `;DB_CLOSE_DELAY=-1` only when it must survive connection closure; H2 then retains it until `SHUTDOWN` or process exit.

### TCP server

```bash
harlequin -a h2 -U sa "jdbc:h2:tcp://localhost/~/demo"
```

## Options

- `--jar PATH`: Path to the H2 JDBC driver JAR.
- `-U, --user USER`: H2 username; defaults to `sa`.
- `--password PASSWORD`: H2 password; defaults to an empty string.

Prefer a protected Harlequin profile or an environment-variable reference for passwords because command-line arguments may be visible to other local processes.