Mendix Domain Model: How to Structure Your Data

In any application, data forms the backbone of functionality. Whether it's a CRM, an e-commerce portal, or an internal dashboard, how you structure your data determines how efficiently your app performs and scales. In Mendix, the Domain Model is where all data modeling happens—serving as the blueprint for your application's data structure.

In this blog, we’ll walk through what the Mendix Domain Model is, how to structure it effectively, and best practices to ensure your applications are robust and maintainable.

📌 What is the Mendix Domain Model?

The Domain Model in Mendix represents the data layer of your application. It defines:

Entities (like database tables)

Attributes (fields within those entities)

Associations (relationships between entities)

Each Module in Mendix can contain one or more domain models, allowing for modular and reusable design.

🛠️ Creating Entities and Attributes

Each Entity represents a type of data—for example, Customer, Order, or Product.

Within each entity, you define Attributes to store information:

String (e.g., Name)

Integer (e.g., Quantity)

Decimal (e.g., Price)

DateTime (e.g., Created Date)

Enumeration (e.g., Order Status)

You can also configure properties such as default values, required fields, length limits, and validation rules for attributes.

Example:

Entity: Customer

Attributes: FirstName (String), LastName (String), Email (String), DateOfBirth (DateTime)

🔗 Understanding Associations

In Mendix, Associations define relationships between entities and help structure complex data.

Types of associations:

One-to-One

One-to-Many

Many-to-Many

For instance:

A Customer may place many Orders (One-to-Many)

An Order may contain many Products (Many-to-Many)

These associations allow you to retrieve, navigate, and display related data across your app.

📦 Using System and Inheritance

Mendix includes System entities like Account, FileDocument, and Image that can be reused across apps.

You can also apply Inheritance to extend base entities. For example:

A base entity User could be extended into Customer and Employee for different roles.

This promotes reusability and reduces redundancy in your model.

💡 Best Practices for Structuring Your Data

Modularize Your Domain Model

Use multiple modules to logically separate data models (e.g., one for Users, another for Orders).

Use Proper Naming Conventions

Keep entity and attribute names clear and meaningful, e.g., InvoiceDate instead of just Date.

Normalize Where Needed

Avoid storing the same data in multiple places. Use associations to link related data instead.

Limit Attribute Count per Entity

Don’t overload entities with too many attributes. Split them into related entities if needed.

Secure Your Data

Use Access Rules to control who can read or write each entity, based on user roles.

Leverage Enumerations

Use Enums instead of free-text fields for fixed lists like statuses or categories to reduce errors.

📈 Real-World Example

Let’s model a Library Management App:

Entities: Book, Member, Loan

Associations:

A Member can borrow many Books through Loan (Many-to-Many)

Loan includes StartDate, DueDate, and ReturnDate

This structure allows you to easily query borrowed books, overdue returns, and member histories.

🏁 Conclusion

The Mendix Domain Model is a critical part of app development. A well-structured domain model not only enhances performance but also simplifies logic, UI, and scalability. By understanding how to structure entities, attributes, and associations thoughtfully, you can build powerful, maintainable Mendix applications that meet your business needs.

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