database-connections

Skill: Create External Database Connections

Purpose

Create and manage external database connections in Mendix using the External Database Connector. This skill helps you set up JDBC connections to external databases (Oracle, PostgreSQL, MySQL, SQL Server, etc.) and define SQL queries that map results to non-persistent entities.

When to Use This Skill

• User asks to connect to an external database from a Mendix app (via JDBC)
• User needs to query data from Oracle, PostgreSQL, MySQL, SQL Server, or other JDBC databases
• User wants to create database connection configurations
• User needs to define SQL queries with parameter binding
• User wants to map query results to Mendix entities

Tip: Use generate connector to auto-create all constants, entities, and queries from a database schema:

SQL CONNECT postgres 'postgres://user:pass@host/db' AS source;
SQL source GENERATE CONNECTOR INTO MyModule;
-- Or generate for specific tables and execute immediately:
SQL source GENERATE CONNECTOR INTO MyModule TABLES (employees, departments) EXEC;

For manual exploration, use sql source show tables; and sql source describe tablename;.

Prerequisites

1. Required Mendix Version

• Mendix 9.22+ (Database Connector introduced)
• Mendix 10.10+ (stable version recommended)

2. Required Non-Persistent Entities

Database query results must be mapped to NON-PERSISTENT entities. Create these first:

-- Entity to hold query results
create non-persistent entity MyModule.EmployeeRecord (
  EmployeeId: integer,
  EmployeeName: string(100),
  Department: string(50),
  Salary: decimal
);

3. Required Constants

Connection credentials should be stored in constants:

-- Connection string (JDBC URL)
create constant MyModule.DbConnectionString type string
  default 'jdbc:oracle:thin:@//hostname:1521/SERVICENAME'
  comment 'JDBC connection string for external database';

-- Username
create constant MyModule.DbUsername type string
  default 'app_user'
  comment 'Database username';

-- Password (use PRIVATE for local development)
create constant MyModule.DbPassword type string
  default ''
  comment 'Database password - inject via environment variable in production'
  PRIVATE;