EMF Validation for Datatype constraints

August 26, 2014 | 2 min Read

After defining a model, it is a common next step to define validation rules. Often there is a requirement to have attributes with a restricted length or attributes with values in a specific range. Furthermore, it can be the case, that there are multiple attributes with the same restriction in different places of the model. To solve such a requirement EMF offers a simple solution: EDataTypes with Annotations.

This is a step-by-step guide how to define your own restricted DataType.

First, you need to define a DataType:


Then the properties of the DataType must be set, this includes the actual Type (the Instance Type Name) and the new Name of the custom DataType:

In the next step, you must define the constraints with an Annotation on the DataType:


In the properties of the Annotation, the source must be set to “https:///org/eclipse/emf/ecore/util/ExtendedMetaData”:

 To define the constraints, a Details Entry must be added to the annotation:

You can add multiple Details Entries, if multiple constraints must be set e.g. the lower and upper bounds of a range restriction.

The key of the Details Entry corresponds to the constraint type and the value corresponds to the constraint value:

  The complete DataType definition looks like this:

 You can now use this definition as an attribute type of any EAttribute in the model:

An attribute with such an AttributeType will automatically provide validation results, e.g. via the Diagnostician. Therefore, frameworks like EMF Forms will automatically evaluate and display them:

You can find the complete list of possible keys in the documentation. Just search for “Facet” and look at the “details key”.

For your convenience, the most important ones are:

  • pattern: allows to define a regular expression which must be met

  • totalDigits: allows to define the maximal number of digits of a number

  • minLength: allows to define the minimal length of a value

  • maxLength: allows to define the maximal length of a value

  • minExclusive: allows to define a minimal value which is still invalid

  • maxExclusive: allows to define a maximal value which is already invalid

  • minInclusive: allows to define a minimal value which is already valid

  • maxInclusive: allows to define a maximal value which is still valid

Have fun defining your DataTypes with custom restrictions!

Jonas, Maximilian and Philip

Jonas, Maximilian and Philip

Jonas Helming, Maximilian Koegel and Philip Langer co-lead EclipseSource. They work as consultants and software engineers for building …