Implement Mendix Best Practices for Development

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1 Introduction

This document can be used as a reference for adopting consistent naming and modeling conventions while developing your Mendix applications. This will help to improve your application’s maintainability and performance, and make it easier to read and understand.

Even with the powerful navigation and search support in Mendix Studio Pro, adhering to naming and modeling conventions is a wise thing because:

  • After finishing an application, it is usually handed over to different people for maintenance, so even years later, they will need to understand what you did and how to improve on it
  • Anybody should be able to quickly understand an existing app in terms of what is located where and how the different parts are related
  • A clear structure helps in identifying reusable code

2 Project Setup

2.1 The Application Development Language

The language that will be used to develop the application should be determined upfront. This way you have one language for modules, entities, microflows, pages, etc. The preferred language for development is English.

There are some reasons why certain parts of an application may use another language. The main reason to make an exception would be within the domain model of an integration module. For example, when the source data model is in another language already.

For more information, see How to Translate Your App Content.

2.2 Project Name

Every project is named when it is created. Make sure you use a logical name that allows you to easily identify the application. You will probably create more projects in the future, and will want to be able to recognize this project. We recommend leaving out dates or Mendix version numbers in the project name, since that information can be captured and extracted in a different way.

2.3 Configurations

Every project has at least one configuration, but it may have many. Every project starts with a single configuration called default. When you work with multiple people on an application it is beneficial to create multiple configurations. When doing so, we recommend using relevant names for those configurations, like the name of the developer or the app’s purpose, like Test or Acceptance. Beware that the database passwords defined in the configuration will be visible to other team members, so be careful with using personal passwords you’d like to keep secret.

2.4 User Roles

The user roles should have logical names that reflect the different types of users that will use the application. The user roles are singular and use a camel case notation, like FunctionalAdministrator. User roles are mostly defined in English, but there is an option to name these in a different language, since the user role is visible in the front-end.

Each user role should correspond to only one module role per module. In other words, a user role should not map to multiple module roles within the same module. This helps to keep the number of applicable module roles for a user to a minimum, which reduces complexity in understanding the security model and reduces the performance impact of complex security rules.

3 Naming Conventions

3.1 Modules

3.1.1 Module Names

Modules should be treated like stand-alone replaceable services; for example, the customer module should function as a stand-alone customer management system as much as possible, replaceable by a different customer management system. Module names should have camel case names that identify the responsibility of the module, for example, CustomerManagement or SharePointIntegration.

3.1.2 Module Roles

The module roles should have logical names that reflect the access they should have within a module. In contrast to the user role, the module role should always be in English, for instance Administrator or Employee.

3.2 Domain Model

3.2.1 Entity Names

Most of the time, an entity reflects a real-world object that people can relate to. Therefore, the entity name should also reflect that object and identify its purpose. There are sometimes project-specific exceptions that lead to creating other types of entity, but that is up to you. The name of an entity is singular since an object is a single instance of the entity. A good example is using Customer and not Customers. Furthermore, we advise avoiding abbreviations, underscores, mathematical characters or any other special characters in the names of entities. Entity names also use camel case, for example, HousekeepingRecord or LogEntry.

3.2.2 Entity Attributes

The entity attribute should reflect a property of a real-world object that people can relate to and fits the purpose of that property. We advise avoiding abbreviations, underscores (except in the case described in the next paragraph), mathematical characters or any other special characters in the names. Entity attributes should use camel case, for example, FirstName or TelephoneNumber.

Attributes that do not reflect business-related data, but are only necessary for technical reasons, should start with an underscore (_).

3.2.3 Associations

3.2.3.1 Naming Multiple Associations Between Entities

Association names in the domain model are automatically generated by Mendix. The auto-generated names follow the best practice and should be used by default.

If you have multiple associations between the same entities we recommend extending the association name. Extending this name with a recognizable purpose clarifies where you should use the association. For example, you can have a relationship between Person and Address. A person can have multiple addresses but you want to specify what their postal address is and what their delivery address is. An implementation choice could be that you create two associations for that purpose and adjust the names of the associations accordingly. For example, Person_Address_Delivery.

3.2.3.2 Renaming Entities

When an association already exists between entities and you change the name on one or both of the entities, Mendix will rename the association automatically.

With models built in lower versions of Mendix, however, you will need to manually rename the assocation to keep your model consistent and up-to-date.

3.3 Folders

The structure for your documents starts with a clear separation of folders. By using a good folder structure you will improve the maintainability of your application; you will be able to find required documents faster and therefore will be able to develop and fix faster.

The optimal grouping of your documents into folders depends on the circumstances and on the functionality of your application. We recommend combining the guidelines below in a way that fits your project.

Every project consists of processes. Structure your documents for these processes into folders that reflect individual processes and their steps.

Every project has documents that are needed for specific entities. Think of overview pages for maintenance, validation microflows that prevent commits, or other event triggers. These types of document should be structured into one folder that is named after the entity. Optionally, sub-folders could be used to organize, for example, events and pages.

3.4 Microflows

Generally, microflow names should include the type of event which triggers them, the name of the main entity being processed, and the operation being performed: {Prefix}_{Entity}_{Operation}. For example, Act_Vendor_StartWorkflow.

There are exceptions, such as where there is no main entity, or there is another reason to use a different name to improve understandability. The important thing is to make sure the name of the microflow clearly indicates its purpose.

To easily find and recognize the purpose of a microflow, you can use standard prefixes. Common purposes or events and their standard prefixes are listed below. If a microflow is triggered by several events you can consider using more than one prefix.

3.4.1 Entity Event Microflows

For some entities you use entity events that are always triggered when a specific operation is executed on the entity.

For example, an attribute TotalOrderAmount is automatically filled based on the amount values of the order-related order lines. You can define an after-commit event that ensures that TotalOrderAmount is updated when a related order line is saved: ACo_Order_CalculateTotalOrderAmount.

The microflows related to such an event handler should have the following prefixes:

Event Type Prefix
Before commit BCo_{Entity name}
After commit ACo_{Entity name}
Before create BCr_{Entity name}
After create ACr_{Entity name}
Before delete BDe_{Entity name}
After delete ADe_{Entity name}
Before rollback BRo_{Entity name}
After rollback ARo_{Entity name}

3.4.2 Calculated Attribute Microflows

For attributes, you can choose to store the value in the database or to calculate the value based on a microflow. For the microflow which does the calculation you should use Cal_ as a prefix, and refer to the entity and attribute which is being calculated. The calculation is triggered when you show the entity on a page or use it in a microflow. On a page, the object’s calculation attribute refreshes if you navigate away from the object and back to it in any way (via pagination buttons or tabs or by re-entering the page).

Event Type Prefix
Calculation Cal_{Entity name}_{Attribute name}

3.4.3 Page-Based Microflows

Pages have a number of events that can trigger a microflow. See the following list for the examples and prefixes:

Event Type Prefix Used In
On enter event OEn_{Purpose} Input widgets
On change event OCh_{Purpose} Input widgets
On leave event OLe_{Purpose} Input widgets
Data source DS_{Purpose} Data view, list view, data grid, template grid
Microflow/action button ACT_{Purpose} or IVK_{Purpose} Menu item, Navigation item, Microflow and Action button, Drop down button
(“IVK_” is used historically)

3.4.4 Validation Microflows

Microflows that are used for data validation use the prefix Val_.

Event Type Prefix
Validation Val_

3.4.5 Scheduled Event Microflows

For the microflow that you use in your scheduled events, use the prefix ScE_. The event itself should have a descriptive name since it will be shown in the cloud configuration portal. The scheduled event and the microflow should have the same name.

Event Type Prefix
Scheduled Event ScE_

3.4.6 Project Microflows

Your project settings provide three events that can trigger a microflow. In these cases we advise writing out the purpose as a microflow name. These microflows are defined only once per project and should preferably call sub-microflows to do the actual processing. These sub-microflows should have a prefix indicated below:

Event Type Microflow Name Sub-microflow Prefix
After startup AfterStartUp ASu_
Before shutdown BeforeShutDown BSd_
Health check HealthCheck HCh_

3.4.7 Unit Test Microflows

Microflows containing unit tests should have the prefix Test_.

Event Type Prefix
Unit Test Test_

3.4.8 Integration Microflows

For integrations, you have the following types of microflow:

Event Type Prefix
Consumed web service operation microflow CWS_
Published web service operation microflow PWS_
Published app service operation microflow PAS_
Published REST service operation microflow PRS_

3.5 Other Document Types

3.5.1 Layouts & Snippets

Layouts and snippets should be identified with prefixes.

Document Type Prefix
Layout Lay_
Snippet Snip_

3.5.2 Enumerations

Enumerations should be identified with a prefix.

Document Type Prefix
Enumeration Enum_

3.5.3 Pages

Pages use a suffix to indicate their use.

Pages that show an overview of a single entity should have a suffix of _Overview.

Pages that are to create, edit, or view entity data, and that are not part of a process, should have the suffix _New_Edit_NewEdit, or _View.

Pages that are used to make a selection of one object have a suffix of _Select where the multi-object selection pages should have the suffix _MultiSelect.

Pages that are used as a tooltip page should have the suffix _Tooltip.

Page Purpose Suffix
List objects of a single entity type _Overview
Create an object _New
Update an object _Edit
Create or Update an object _NewEdit
View an object (read-only) _View
Select a single object _Select
Select multiple objects _MultiSelect
Tooltip _Tooltip

3.5.4 Integration Documents

Documents used to support integration should have the prefixes listed below.

Document Type Prefix
Import mapping ImM_
Export mapping ExM_
XML schema XSD_
JSON structure JSON_
Deeplink Dl_

3.6 Home Pages

You can define the home pages per device and role in your navigation. The recommended page names are listed below:

Event Type Device Page Name
Default home page Desktop Home_Desktop_Default
Default home page Tablet Home_Tablet_Default
Default home page Mobile Home_Phone_Default
Role based home page Desktop Home_Desktop_{Userrole}
Role based home page Tablet Home_Tablet_{Userrole}
Role based home page Mobile Home_Phone_{Userrole}

4 General Guidelines & Best Practices

4.1 Domain Models

4.1.1 Attributes

Using calculated (virtual) attributes is discouraged. These introduce a performance risk since they need to be calculated every time the object is used, regardless of whether the attribute itself is used.

4.1.2 Inheritance

When using inheritance (specialization/generalization), it is recommended to use no more than two levels for performance reasons.

4.1.3 Delete Behavior

Delete behavior must be specified where possible. Delete behavior must, however, never be relied upon when deleting large amounts of data. For performance reasons it is better to explicitly delete dependent objects when doing batch deletes.

4.1.4 Event Handlers

Event handlers on domain entities must be used with a lot of caution. They can quickly result in complex and possibly unexpected behavior when several of them are applied to a single entity. It is often best to make the execution of microflows more explicit by using sub-microflows that are called manually, for example, just before committing an object.

4.2 Microflows

4.2.1 Size

The size of a microflow should not exceed 25 elements. An element is any block that Studio Pro allows in a microflow (loops, action activities, decisions, etc.). In some cases exceeding this limit is acceptable; this can occur, for instance, for validation or data copying flows.

Split microflows up into logical, functional elements. If a microflow has more than twenty-five elements, split the microflow up by creating a sub-microflow for a part of it. For example, by separating presentation logic from business logic.

Certain cases (such as validation checks) may require this rule to be ignored to produce an understandable result.

4.2.2 Documentation & Annotations

All complex microflows (more than ten activities or more than two decisions) should have an annotation describing the purpose of the microflow, expected parameters, and return values. This annotation should be placed at the start, so it is visible when the microflow is opened. This will assist other developers in quickly understanding the general purpose of a microflow, without having to read through it entirely.

Complex, non-standard or integration-related sections in microflows should also have an accompanying annotation. Examples of these are web service calls, custom loops, and Java calls.

4.2.3 Readability

The normal flow in a microflow should be aligned from left to right to ensure readability. Exceptions to the normal flow may branch out vertically: downwards is preferred, upwards if the downwards direction is already used.

Avoid crossing of lines of the links between the microflow elements.

If you decide to color code the different activities in your project, be sure to align within your team on their meaning.

4.2.4 Complexity

Nested IF statements in a single microflow expression are not recommended. If multiple checks depend on one another, this should be represented by multiple decisions in the microflow, so that the complexity is not hidden away in the expressions. You can use AND and OR operators to produce complex expressions if necessary.

Event triggers on input fields must be kept as simple as possible, since they are potentially executed very often, depending on user behavior. Complex operations here will reduce performance.

The number of parameters for a microflow should be kept to a minimum to facilitate reusability. The more parameters a microflow has, the more difficult it is to determine what should be put into the parameters to make the microflow run correctly.

4.2.5 Error Handling & Logging

Use microflow error handling for all integration and Java calls. Make sure to determine the correct rollback behavior. Always log the error that occurred, even if the process can continue, this is essential for later analysis of the error.

Complex processes and important business logic (like workflow processing or validations) must include debug and trace logging. Logging actions must write the current state and progress of the process and must include a request ID or other identifying information. The log node should be the name of the module. This will greatly assist error analysis.

4.3 Warnings & Studio Pro Feedback

No warnings should be visible in Studio Pro, unless explicitly documented with a reason. Warnings can indicate many issues, including maintainability and security risks, which must be resolved.

Unused and excluded items should be removed from the model when they are no longer needed. When a version of the application is prepared for a release, all these items should be cleaned up. Make sure to check whether items that appear unused are not actually called from a Java action before removing them. Studio Pro provides the possibility to mark such items as used to override warnings about this.

4.4 XPath

XPath constraints in any part of the model should be kept as simple as possible. As a general rule, XPaths must not appear when the Find advanced > XPath option in Studio Pro is used with all options enabled.

When an XPath needs multiple constraints, each constraint must be put in brackets ([ ]) separately, instead of using the and keyword. This also applies to sub-constraints.

4.5 Security

The security overview in Studio Pro must not show any incomplete (yellow) parts. All entity, microflow, and page access must be configured completely.

Assigning default rights to new members when defining entity access is NOT recommended. This will ensure that access is only granted after a conscious decision.

4.6 Mendix Version

Apps should keep up with new Mendix releases as much as possible.

4.7 App Store Content

When introducing a new Mendix App Store component to a project, carefully consider the support level of the component. Using components that are community supported introduces a maintainability and upgrade risk.

App Store modules should NOT be modified. If an App Store module is modified, updating to a new version becomes much harder, because the changes will be overwritten when a new version is downloaded from the App Store. If changing an App Store module is unavoidable, you have two options:

  • Mark any changes you make explicitly and clearly, and perform them again when the module is updated
  • Copy the contents of the App Store module to another module in your app and use that module instead (remember that your app will no longer reflect updates to the original App Store module)

To minimize the number of changes in the actual App Store module, it is advisable to combine them in a separate extension module wherever possible.