Entities

Entities are the primary data structures in a Mendix domain model. Each entity corresponds to a database table (for persistent entities) or an in-memory object (for non-persistent entities).

Entity Types

Type	MDL Keyword	Description
Persistent	`PERSISTENT`	Stored in the database with a corresponding table
Non-Persistent	`NON-PERSISTENT`	In-memory only, scoped to the user session
View	`VIEW`	Based on an OQL query, read-only
External	`EXTERNAL`	From an external data source (OData, etc.)

CREATE ENTITY

[/** <documentation> */]
[@Position(<x>, <y>)]
CREATE [OR MODIFY] <entity-type> ENTITY <Module>.<Name> (
  <attribute-definitions>
)
[INDEX (<column-list>)]
[;|/]

Persistent Entity

The most common type. Data is stored in the application database:

/** Customer entity */
@Position(100, 200)
CREATE PERSISTENT ENTITY Sales.Customer (
  CustomerId: AutoNumber NOT NULL UNIQUE DEFAULT 1,
  Name: String(200) NOT NULL ERROR 'Name is required',
  Email: String(200) UNIQUE ERROR 'Email must be unique',
  Balance: Decimal DEFAULT 0,
  IsActive: Boolean DEFAULT TRUE,
  CreatedDate: DateTime,
  Status: Enumeration(Sales.CustomerStatus) DEFAULT 'Active'
)
INDEX (Name)
INDEX (Email);

Non-Persistent Entity

Used for helper objects, filter parameters, and UI state that does not need database storage:

CREATE NON-PERSISTENT ENTITY Sales.CustomerFilter (
  SearchName: String(200),
  MinBalance: Decimal,
  MaxBalance: Decimal
);

View Entity

Defined by an OQL query. View entities are read-only:

CREATE VIEW ENTITY Reports.CustomerSummary (
  CustomerName: String,
  TotalOrders: Integer,
  TotalAmount: Decimal
) AS
  SELECT
    c.Name AS CustomerName,
    COUNT(o.OrderId) AS TotalOrders,
    SUM(o.Amount) AS TotalAmount
  FROM Sales.Customer c
  LEFT JOIN Sales.Order o ON o.Customer = c
  GROUP BY c.Name;

CREATE OR MODIFY

Creates the entity if it does not exist, or updates it if it does. New attributes are added; existing attributes are preserved:

CREATE OR MODIFY PERSISTENT ENTITY Sales.Customer (
  CustomerId: AutoNumber NOT NULL UNIQUE,
  Name: String(200) NOT NULL,
  Email: String(200),
  Phone: String(50)  -- new attribute added on modify
);

Annotations

@Position

Controls where the entity appears in the domain model diagram:

@Position(100, 200)
CREATE PERSISTENT ENTITY Sales.Customer ( ... );

Documentation

A /** ... */ comment before the entity becomes its documentation in Studio Pro:

/** Customer master data.
 *  Stores both active and inactive customers.
 */
CREATE PERSISTENT ENTITY Sales.Customer ( ... );

DROP ENTITY

Removes an entity from the domain model:

DROP ENTITY Sales.Customer;

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