Change Things in the Model

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1 Introduction

All units and elements can be freely altered after loading as long as you adhere to the type system. The properties id, container, structureTypeName, isLoaded and unit, as defined on the IStructure object, should not be used: these are (mostly) for internal purposes.

2 Creating New Units & Elements

To create new units, you need to pass the parent structural unit to the constructor.

To create new elements, use the create methods, as this will create an element detached from the model. Please note that after creating an element, you have to assign it to a property before it actually becomes part of your model. For example, a new Attribute element should be pushed onto the attributes array of an entity. If you want to create an element and attach it to the model directly, you can use createIn.

An element is always in a specific state: new, attached, detached, or deleted. The state determines what changes can be applied to the element. For a full description of these states and their characteristics, see the Element States section below.

All non-list-like properties can be altered simply using assignments. List-like properties are essentially JavaScript arrays, so to alter them you can just replace them or use JavaScript’s built-in array functions such as push.

References are automatically resolved by the SDK. This means you can just assign or read references directly using fully-typed objects. For each property that refers to a concept in another unit, there is also a read-only property available with <propertyName>QualifiedName (or <propertyName>QualifiedNames for list-like properties) that gives the string representation of the references.

The following example function creates a new entity with an attribute given a domain model:

import { domainmodels } from "mendixmodelsdk";

function createEntity(domainModel: domainmodels.DomainModel, entityName: string, attributeName: string) {
    const newEntity = domainmodels.Entity.createIn(domainModel); = entityName;

    // location on the canvas in the Mendix Studio Pro:
    newEntity.location = { x: 100, y: 100 };

    // new attribute (which is by default a string attribute):
    const newAttribute = domainmodels.Attribute.createIn(newEntity); = attributeName;

3 Element States

An element can be in four different states. The state determines what can be done with the element.

3.1 States

3.1.1 New

The new state signifies that an element has been created and has not yet been added to a model. A new element does not need to be added to a model, it can be “forgotten”.

New elements can be added as parts of other new elements. They will then retain their new state. This only applies to elements with the state new; detached elements cannot be added to new elements.

When an element in the new state is attached to a model, the element and all of its parts will get the attached state.

When a new element is added to a detached element, the new element and its parts get the state attached.

An element in the new state cannot become detached.

3.1.2 Attached

The attached state signifies that an element is part of a model or is part of a detached element.

When an element becomes part of a model, it gets the attached state. All access is allowed, as this is the “normal” situation. Rules (for example, about being required) are taken into account.

If an element gets the attached state, all of its parts also get the attached state.

3.1.3 Detached

The detached state signifies that an element has been part of a model and is temporarily not part of a model.

You cannot detach an element with the new state.

A detached element must be attached to a model again within the same (implicit) transaction.

Most access is allowed, just as in the attached state:

  • Property access, and change are allowed
  • Elements in a detached tree can be detached or deleted from the tree again

In contrary to the attached state, an element with the detached state cannot become deleted.

Rules (for example, about being required) are taken into account.

If an element is being detached, its parts stay in their original (attached) state.

A detached element can be attached to an attached element. A detached element cannot be attached to a new element; the new element should be attached first.

If a detached element is attached to a model, the element becomes attached. All of its parts that have the attached state stay in this state.

3.1.4 Deleted

The deleted state signifies that the element has been deleted from the model.

All write access to a deleted element is forbidden and will throw an error.

All the parts of a deleted element are also deleted and cannot be accessed. If an element gets the state deleted, all of its parts will also get the deleted state.

3.2 Overview of Allowed State Changes

Starting State To new To attached To detached To deleted
new - Allowed Not allowed Allowed
attached Not allowed - Allowed Allowed
detached Not allowed Allowed - Not allowed
deleted Not allowed Not allowed Not allowed -

4 Next Step

Continue with How to Close the Server Connection.