Data Types

MDL has a type system that maps to the Mendix metamodel attribute types. Every attribute in an entity definition has a type that determines how values are stored and validated.

Type Categories

Quick Example

CREATE PERSISTENT ENTITY Demo.AllTypes (
  Id: AutoNumber NOT NULL UNIQUE DEFAULT 1,
  Code: String(10) NOT NULL UNIQUE,
  Name: String(200) NOT NULL,
  Description: String(unlimited),
  Counter: Integer DEFAULT 0,
  BigNumber: Long,
  Amount: Decimal DEFAULT 0.00,
  IsActive: Boolean DEFAULT TRUE,
  CreatedAt: DateTime,
  BirthDate: Date,
  Attachment: Binary,
  Status: Enumeration(Demo.Status) DEFAULT 'Active'
);

No Implicit Conversions

MDL does not perform implicit type conversions. Types must match exactly when assigning defaults or modifying attributes.

Compatible type changes (when using CREATE OR MODIFY):

• String(100) to String(200) – increasing length
• Integer to Long – widening numeric type

Incompatible type changes:

• String to Integer
• Boolean to String
• Any type to AutoNumber (if data exists)

Further Reading

• Primitive Types – detailed reference for each type
• Constraints – NOT NULL, UNIQUE, DEFAULT
• Type Mapping – MDL to Mendix to database mapping
• Enumerations – enumeration type definitions