harlequin-h2

A Harlequin adapter for H2 databases via JDBC. It supports embedded file and memory databases as well as H2 TCP and TLS servers.

The adapter embeds the JVM with JPype and talks to H2 directly. File and memory connections do not require a database server, protocol bridge, or fixed port.

Requirements

• Python 3.10 or later
• Harlequin 2.9 or later, below 3.0
• H2 2.x
• A Java runtime compatible with your H2 version
• The H2 JDBC driver JAR

Installation

Install H2 and add this adapter to the same environment as Harlequin:

brew install h2
uv tool install harlequin --with harlequin-h2

If Harlequin is already installed with uv, add the adapter to that tool environment:

uv tool install harlequin --with harlequin-h2 --force

The adapter finds Homebrew's H2 JAR automatically. On other platforms, pass --jar or set H2_JAR:

export H2_JAR=/path/to/h2.jar

Usage

Embedded file database

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

AUTO_SERVER=TRUE allows Harlequin and another JVM process to share the file. Use IFEXISTS=TRUE when inspection must never create a new empty database due to a mistyped path.

Embedded memory database

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

A named embedded memory database normally exists until its last connection is closed. Add ;DB_CLOSE_DELAY=-1 only when it must survive connection closure; H2 then retains it until SHUTDOWN or process exit.

TCP or TLS server

harlequin -a h2 -U sa "jdbc:h2:tcp://localhost/~/demo"
harlequin -a h2 -U sa "jdbc:h2:ssl://db.example.com/~/demo"

Options

Prefer a protected Harlequin profile or an environment-variable reference for passwords. Command-line arguments may be visible to other local processes. Harlequin 2.10 and later also mask this option in configuration output and prompts.

Environment variables in the JDBC URL are expanded before connecting:

export H2_DATABASE_DIR=/absolute/path/to/databases
harlequin -a h2 'jdbc:h2:file:$H2_DATABASE_DIR/demo;IFEXISTS=TRUE'

Features

• Query execution and result display
• Lazy schema, table, view, and column catalog
• Data preview, column insertion, relation description, and DDL actions
• Safe query execution and result fetching across Harlequin worker threads

License

MIT