demo-data

Skill: Connect to Application Database and Generate Demo Data

Purpose

Connect directly to the Mendix application's PostgreSQL database from a devcontainer and insert demo data — bypassing the runtime. Covers reading DB settings, understanding Mendix's internal ID system, and safely inserting rows with correct IDs and association links.

When to Use This Skill

• User asks to seed or populate the database with test/demo data
• User needs data in the app before the UI is built
• User wants to inspect the database directly (schema, row counts, etc.)
• Bulk data import that is impractical through the Mendix UI

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Step 1: Get Database Settings

Use mxcli to read the project's configured database connection:

./mxcli -p <project>.mpr -c "show settings;"

Example output:

| configuration 'Default' | PostgreSql, localhost:5434, db=mxcli2-dev, http=8080 |

For full credentials (username, password):

./mxcli -p <project>.mpr -c "describe settings;"

Example output:

alter settings configuration 'Default'
  DatabaseType = 'PostgreSql',
  DatabaseUrl = 'localhost:5434',
  DatabaseName = 'mxcli2-dev',
  DatabaseUserName = 'mendix',
  DatabasePassword = 'mendix',
  HttpPortNumber = 8080;

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Step 2: Connect to the Database

From a devcontainer on macOS

The Mendix app's localhost in the project settings refers to the Mac host, not the devcontainer. Use host.docker.internal to reach it:

PGPASSWORD=mendix psql -h host.docker.internal -p 5434 -U mendix -d mxcli2-dev

Useful psql commands

# list all tables
\dt

# describe a table
\d tasklist$task

# run a query and exit
PGPASSWORD=mendix psql -h host.docker.internal -p 5434 -U mendix -d mxcli2-dev \
  -c "select * from \"tasklist\$task\" limit 5;"

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Step 3: Understand the Mendix ID System

Every Mendix object has a bigint ID composed of three parts:

| bits 63–48  | bits 47–7            | bits 6–0       |
|  entity ID  |  sequence number     |  random         |
| (16 bits)   |  (41 bits)           |  (7 bits)       |