Connect Chat2DB Community to Google BigQuery

This guide shows how to add a BigQuery connection in Chat2DB Community and run your first query.

BigQuery is a fully managed cloud data warehouse from Google. Chat2DB connects to it through the Simba JDBC driver and authenticates using a Google Cloud service account.

Prerequisites

Before you start, you need:

• A Google Cloud project. A billing account is recommended for full functionality; BigQuery's sandbox lets you try the service without a billing account, with stricter limits. The BigQuery free tier covers the first 1 TiB of query data processed and 10 GiB of storage per month, so the steps in this guide stay inside the free tier.
• A service account with roles/bigquery.user (BigQuery User) on the project used to run query jobs. To query existing tables, it also needs a data-access role such as roles/bigquery.dataViewer (BigQuery Data Viewer) on the datasets it may read.
• A service account key in JSON form. The guide explains how to create one below.
• Chat2DB Community running locally, through Docker, or as the desktop app. See the main README for setup.

You do not need a Java or Maven setup to follow this guide. Chat2DB downloads the JDBC driver on first connection.

Create a service account key

The service account is what Chat2DB uses to authenticate to BigQuery. Treat its JSON key like a password.

Prerequisites

Before you start, your user account needs the Service Account Key Admin role (roles/iam.serviceAccountKeyAdmin) on the project, per the Google Cloud IAM documentation. Your organization may also enforce a policy that disables key creation; if so, follow the policy override steps in the same page.

Steps in the Google Cloud console

The official Google Cloud documentation sends you through a guided console walkthrough rather than enumerating each step inline, because the console UI changes over time. The current path is roughly:

1. In the Google Cloud console, open IAM and Admin → Service Accounts for the project you want to connect to.
2. Click Create service account, give it a name such as chat2db-reader, and click Create and continue.
3. Grant the BigQuery User role (roles/bigquery.user) on the project used to run query jobs, then click Continue and Done.
4. Open the new service account, switch to the Keys tab, click Add key → Create new key, and choose JSON. The browser downloads a file that ends in .json.
5. Store the file somewhere only your user account can read, for example ~/.config/chat2db-community/keys/.

To query tables, grant the service account BigQuery Data Viewer (roles/bigquery.dataViewer) on each dataset it should read. BigQuery User can create query jobs, but it does not by itself grant permission to read table data. See Google's BigQuery access-control documentation for narrower custom-role options.

If your console layout looks different, follow the official walkthrough instead — it always reflects the current UI.

Do not commit this file to any repository, and do not paste its contents into chat, screenshots, or issue trackers. If the file leaks, delete the key in Google Cloud and create a new one.

Connection configuration

In Chat2DB, open the connection dialog and choose BigQuery as the database type. The form shows the fields below. Every field is taken from the current Community plugin defaults at chat2db-community-server/chat2db-community-plugins/chat2db-community-bigquery/src/main/resources/ai/chat2db/plugin/bigquery/bigquery.json and the field wiring in BigQueryDBManager.java.

The plugin translates your input to the following JDBC properties before opening the connection:

• ProjectId from the Project field.
• OAuthServiceAcctEmail from the Email field.
• OAuthType=0 and OAuthPvtKeyPath from the Keyfile field. The OAuthType=0 value selects service-account authentication in the Simba driver.

Chat2DB Community ships support for the service account flow only. OAuth user flows (browser sign-in, OAuth refresh tokens) are not currently wired up in the Community plugin, so this guide does not document them.

Keyfile paths in Web and Docker deployments

The Simba driver opens the keyfile from the filesystem of the process running the Chat2DB backend:

• For the desktop app or a backend running directly on your computer, enter an absolute path on that computer.
• For a remote Web deployment, place the keyfile on the backend server. A path on the computer running your browser will not work.
• For Docker, bind-mount the file read-only and enter the container path in Chat2DB. For example, add -v /absolute/host/path/bigquery.json:/run/secrets/bigquery.json:ro to docker run, then use /run/secrets/bigquery.json as Keyfile.

The saved datasource contains the path, not a copy of the JSON credential. Chat2DB does not encrypt or manage the keyfile itself, so keep the file outside the repository and restrict its filesystem permissions.

Test the connection

Click Test connection in the dialog. A success message confirms that the driver downloaded, the service account authenticated, and the project is reachable.

To run the cheapest safe query once the connection is saved, open a new SQL tab and run:

SELECT 1 AS ok;

This query does not read any tables, does not scan data, and does not require any dataset to exist. It processes essentially zero bytes, which puts it inside BigQuery's free tier, so it does not bill the project.

Query example

BigQuery uses backtick-quoted fully qualified table names of the form `project.dataset.table`. A useful first query is to list tables in a dataset:

SELECT table_name
FROM `your-project.your_dataset.INFORMATION_SCHEMA.TABLES`
ORDER BY table_name
LIMIT 50;

Replace your-project with your GCP project ID and your_dataset with a dataset the service account can read. To run the query, press Run or use the keyboard shortcut configured in Chat2DB.

Troubleshooting

These are the failures users hit most often when connecting Chat2DB Community to BigQuery. Each fix is based on either the plugin's own configuration (bigquery.json) or the way the plugin maps form fields to JDBC properties (BigQueryDBManager.java). The exact error text returned by the Simba driver and Google APIs can vary between versions, so match by category rather than verbatim wording.

Driver class not found on first connect

The Simba JDBC driver archive is downloaded the first time Chat2DB talks to a BigQuery connection. If the runtime cannot reach cdn.chat2db-ai.com, the download fails and the connection cannot open. Allow that host, then click Test connection again. The driver archive filename is SimbaJDBCDriverforGoogleBigQuery42_1.6.1.1002.zip and the driver class is com.simba.googlebigquery.jdbc42.Driver, both defined in bigquery.json.

Access denied or permission errors

The service account may be missing roles/bigquery.user on the query project, or it may lack roles/bigquery.dataViewer (or equivalent permissions) on the dataset being queried. Re-check both the Project field and the dataset-level access grant.

Invalid JWT, invalid grant, or private key parsing errors

The Keyfile value is wrong or is not visible to the backend process. The plugin passes it straight to the JDBC property OAuthPvtKeyPath, which the Simba driver treats as a path to a JSON file. Confirm the path is absolute, the file exists on the backend or inside the container, the process can read it, and you have not edited the JSON by hand.

Project not found or BigQuery not enabled

The Project field does not match the project ID used for query jobs, or the BigQuery API is not enabled for that project. If the project is brand new, confirm whether billing is linked or whether you want to use the BigQuery sandbox without one.

Billing or sandbox errors

BigQuery normally requires a billing account to be linked to the project. If you prefer to skip billing, the BigQuery sandbox lets you run queries against up to 10 GiB of free storage and 1 TiB of free query processing per month, without attaching a billing account. Either way, queries that scan data still cost the project once the free tier is exhausted. Open Billing for the project in Google Cloud and link an active billing account if you need to go beyond the sandbox limits.

Cannot reach googleapis.com

The Chat2DB backend cannot reach Google APIs. Check DNS, proxy, firewall, and outbound HTTPS access from the backend host or container; testing access in the browser alone does not verify the backend network path.

Security notes

• The service account JSON key is a credential. Store it where only the Chat2DB backend process owner can read it, and never commit it to a Git repository. On Unix-like systems, restrict it with permissions such as chmod 600.
• Chat2DB stores the keyfile path in the datasource configuration. The JSON file remains separate on disk and must be protected with filesystem permissions and, for containers, a read-only mount.
• Grant the service account the smallest roles that work. Use roles/bigquery.user for query-job creation and grant roles/bigquery.dataViewer only on datasets that it needs to read. Use roles/bigquery.dataEditor only when writes are required.
• If you ever paste the JSON contents in a chat, screenshot, or issue tracker, treat the key as compromised. Open Google Cloud, delete the key under the service account's Keys tab, and create a new one.