.equals methods for collection-like elements

[mjacoby]

For some collection-like AAS type classes the equals method does not work as expected, e.g.

Property property1 = new DefaultProperty.Builder()
		.idShort("property1")
		.build();
Property property2 = new DefaultProperty.Builder()
		.idShort("property2")
		.build();
SubmodelElementCollection smc1 = new DefaultSubmodelElementCollection.Builder()
		.value(List.of(property1, property2))
		.build();
SubmodelElementCollection smc2 = new DefaultSubmodelElementCollection.Builder()
		.value(List.of(property2, property1))
		.build();
// expected: true, actual: false
boolean equals = Objects.equals(smc1, smc2);

returns false although SubmodelElementCollection is defined to not be ordered. Same goes for Submodel class.

For SubmodelElementList this issue is more complex as it has the ordered property.

Property property1 = new DefaultProperty.Builder()
		.idShort("property1")
		.build();
Property property2 = new DefaultProperty.Builder()
		.idShort("property2")
		.build();
SubmodelElementList smc1 = new DefaultSubmodelElementList.Builder()
		.value(List.of(property1, property2))
		.build();
SubmodelElementList smc2 = new DefaultSubmodelElementList.Builder()                
		.value(List.of(property2, property1))
		.build();
smc1.setOrderRelevant(false);
smc2.setOrderRelevant(false);
// expected: true, actual: false
boolean equalsWithoutOrder = Objects.equals(smc1, smc2);
smc1.setOrderRelevant(true);
// expected: false, actual: false
boolean equalsWithOrderOneElement = Objects.equals(smc1, smc2);
smc2.setOrderRelevant(true);
// expected: false, actual: false
boolean equalsWithOrder = Objects.equals(smc1, smc2);

All .equals calls return false in this example, whereas equalsWithoutOrder should be true as order should be ignored.

This behavior is not compliant with the current specification.
However, there is a discussion if the specification should be updated to ensure order in such collections (admin-shell-io/aas-specs-metamodel#248).

Before any release we should make sure that we are compliant to the specification.

[twebermartins]

Check the final release spec if this issue has been addressed otherwise discuss internally

[mjacoby]

@mjacoby to check if this issue is now resolved

[mjacoby]

Current status

Issue is not resolved.
Corresponding issue in spec discussion (admin-shell-io/aas-specs-metamodel#248) has been closed but is no concrete answer has been given or given answer contradicts specification. I added a new post asking for clarification.

I also create a corresponding unit test testing the expected behavior according to the spec. It is available on the branch bug/equals https://github.com/eclipse-aas4j/aas4j/blob/bug/equals/model/src/test/java/org/eclipse/digitaltwin/aas4j/v3/model/impl/EqualsTest.java and 7/16 tests are currently failing.

Before updating our implementation we need to clarify the expected behavior with the spec team.

[mhrimaz]

@mjacoby
Other than ordering issue in equals, there is also problem with custom classes.
Equality of class should be replaced by a more generic logic

aas4j/model/src/main/java/org/eclipse/digitaltwin/aas4j/v3/model/impl/DefaultProperty.java

Line 103 in 4c56bbe

} else if (this.getClass() != obj.getClass()) {

can be changed to:
Property.class.isInstance(this)==false|| Property.class.isInstance(obj)==false

aas4j/model/src/main/java/org/eclipse/digitaltwin/aas4j/v3/model/impl/DefaultProperty.java

Line 106 in 4c56bbe

DefaultProperty other = (DefaultProperty) obj;

Furthermore, the casting to DefaultProperty is too restrictive and unnecessary and can be changed to:

Property other = (Property) obj;
return Objects.equals(this.valueType, other.getValueType()) &&
    Objects.equals(this.value, other.getValue()) &&
    Objects.equals(this.valueId, other.getValueId()) &&
    Objects.equals(this.embeddedDataSpecifications, other.getEmbeddedDataSpecifications()) &&
    Objects.equals(this.category, other.getCategory()) &&
    Objects.equals(this.idShort, other.getIdShort()) &&
    Objects.equals(this.displayName, other.getDisplayName()) &&
    Objects.equals(this.description, other.getDescription()) &&
    Objects.equals(this.extensions, other.getExtensions()) &&
    Objects.equals(this.semanticId, other.getSemanticId()) &&
    Objects.equals(this.supplementalSemanticIds, other.getSupplementalSemanticIds()) &&
    Objects.equals(this.qualifiers, other.getQualifiers());

two questions can be raised here:

• is null and empty list equal?
• is null and empty string equal?
  I can help to fix this.