eclipse-syson · AxelRICHARD · Jun 25, 2026 · Jun 24, 2026
diff --git a/CHANGELOG.adoc b/CHANGELOG.adoc
@@ -49,6 +49,7 @@ Now, the choice is restricted to the _timeslice/snapshot_ type that match the gr
 Users should use the dedicated tools to edit expressions instead, as they ensure only valid expressions (with all names resolving) are accepted.
 - https://github.com/eclipse-syson/syson/issues/2287[#2287] [details] Use a label instead of a text field to display Expressions in the Details view.
 - https://github.com/eclipse-syson/syson/issues/2290[#2290] [details] When the selected element can have an expression (but does not), display a widget to indicate it and to allow to create one.
+- https://github.com/eclipse-syson/syson/issues/2301[#2301] [diagram] Constraint nodes now display their corresponding expression directly in their label if it is set.
 
 === New features
 

diff --git a/...pse/syson/application/controllers/expressions/ExpressionsControllersIntegrationTests.java b/...pse/syson/application/controllers/expressions/ExpressionsControllersIntegrationTests.java
@@ -13,6 +13,7 @@
 package org.eclipse.syson.application.controllers.expressions;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.eclipse.sirius.components.diagrams.tests.DiagramEventPayloadConsumer.assertRefreshedDiagramThat;
 import static org.eclipse.sirius.components.trees.tests.TreeEventPayloadConsumer.assertRefreshedTreeThat;
 
 import com.jayway.jsonpath.JsonPath;
@@ -27,28 +28,34 @@
 import java.util.function.Consumer;
 import java.util.function.Supplier;
 
+import org.eclipse.sirius.components.collaborative.dto.CreateRepresentationInput;
 import org.eclipse.sirius.components.core.api.ErrorPayload;
 import org.eclipse.sirius.components.core.api.IEditingContext;
 import org.eclipse.sirius.components.core.api.IIdentityService;
 import org.eclipse.sirius.components.core.api.IInput;
 import org.eclipse.sirius.components.core.api.IObjectSearchService;
 import org.eclipse.sirius.components.core.api.IPayload;
 import org.eclipse.sirius.components.core.api.SuccessPayload;
+import org.eclipse.sirius.components.diagrams.Diagram;
 import org.eclipse.sirius.components.graphql.tests.ExecuteEditingContextFunctionInput;
 import org.eclipse.sirius.components.graphql.tests.ExecuteEditingContextFunctionSuccessPayload;
 import org.eclipse.sirius.components.graphql.tests.api.IExecuteEditingContextFunctionRunner;
 import org.eclipse.sirius.web.application.views.explorer.ExplorerEventInput;
+import org.eclipse.sirius.web.tests.services.api.IGivenCreatedDiagramSubscription;
 import org.eclipse.sirius.web.tests.services.api.IGivenInitialServerState;
 import org.eclipse.sirius.web.tests.services.explorer.ExplorerEventSubscriptionRunner;
 import org.eclipse.sirius.web.tests.services.representation.RepresentationIdBuilder;
 import org.eclipse.syson.AbstractIntegrationTests;
 import org.eclipse.syson.GivenSysONServer;
+import org.eclipse.syson.application.controllers.diagrams.checkers.CheckDiagramElementCount;
+import org.eclipse.syson.application.controllers.diagrams.testers.DropFromExplorerTester;
 import org.eclipse.syson.application.controllers.expressions.graphql.CreateExpressionMutationRunner;
 import org.eclipse.syson.application.controllers.expressions.graphql.DeleteExpressionMutationRunner;
 import org.eclipse.syson.application.controllers.expressions.graphql.EditExpressionMutationRunner;
 import org.eclipse.syson.application.controllers.expressions.graphql.ExpressionTextualRepresentationQueryRunner;
 import org.eclipse.syson.application.data.ExpressionSamplesProjectData;
 import org.eclipse.syson.application.expressions.dto.DeleteExpressionInput;
+import org.eclipse.syson.services.diagrams.DiagramComparator;
 import org.eclipse.syson.services.explorer.api.IExplorerDefaultFiltersSearchService;
 import org.eclipse.syson.sysml.AttributeUsage;
 import org.eclipse.syson.sysml.ConstraintUsage;
@@ -62,6 +69,7 @@
 import org.eclipse.syson.sysml.dto.EditExpressionSuccessPayload;
 import org.eclipse.syson.sysml.metamodel.services.MetamodelQueryElementService;
 import org.eclipse.syson.tree.explorer.view.SysONTreeViewDescriptionProvider;
+import org.eclipse.syson.util.SysONRepresentationDescriptionIdentifiers;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;
@@ -70,6 +78,7 @@
 import org.springframework.test.context.transaction.TestTransaction;
 import org.springframework.transaction.annotation.Transactional;
 
+import reactor.core.publisher.Flux;
 import reactor.test.StepVerifier;
 
 /**
@@ -84,6 +93,9 @@ public class ExpressionsControllersIntegrationTests extends AbstractIntegrationT
     @Autowired
     private IGivenInitialServerState givenInitialServerState;
 
+    @Autowired
+    private DropFromExplorerTester dropFromExplorerTester;
+
     @Autowired
     private ExplorerEventSubscriptionRunner explorerEventSubscriptionRunner;
 
@@ -117,6 +129,12 @@ public class ExpressionsControllersIntegrationTests extends AbstractIntegrationT
     @Autowired
     private DeleteExpressionMutationRunner deleteExpressionMutationRunner;
 
+    @Autowired
+    private IGivenCreatedDiagramSubscription givenCreatedDiagramSubscription;
+
+    @Autowired
+    private DiagramComparator diagramComparator;
+
     private String sysONExplorerTreeDescriptionId;
 
     private MetamodelQueryElementService metamodelQueryElementService;
@@ -585,6 +603,52 @@ public void topLevelExpressionTextualRepresentation() {
                 .verify(Duration.ofSeconds(10));
     }
 
+    private Flux<Object> givenSubscriptionToNewDiagram() {
+        var input = new CreateRepresentationInput(
+                UUID.randomUUID(),
+                ExpressionSamplesProjectData.EDITING_CONTEXT_ID,
+                SysONRepresentationDescriptionIdentifiers.GENERAL_VIEW_DIAGRAM_DESCRIPTION_ID,
+                ExpressionSamplesProjectData.SemanticIds.EXPRESSIONS_PACKAGE_ID,
+                "Diagram");
+        return this.givenCreatedDiagramSubscription.createAndSubscribe(input).flux();
+    }
+
+
+    @DisplayName("GIVEN a SysML model with expressions, WHEN dropping a contraint with an associated expression on an empty diagram, THEN the node showing the constraint includes the text of the exression in its label")
+    @GivenSysONServer({ ExpressionSamplesProjectData.SCRIPT_PATH })
+    @Test
+    public void topLevelConstraintNodeLabelIncludesExpressionInLabel() {
+        var flux = this.givenSubscriptionToNewDiagram();
+
+        AtomicReference<Diagram> diagram = new AtomicReference<>();
+        Consumer<Object> initialDiagramContentConsumer = assertRefreshedDiagramThat(diagram::set);
+
+        Runnable dropFromExplorerRunnable = () -> {
+            assertThat(diagram.get().getNodes()).hasSize(0);
+            var background = diagram.get().getStyle().getBackground();
+            assertThat(background).isNotEqualTo("white");
+            this.dropFromExplorerTester.dropFromExplorerOnDiagram(ExpressionSamplesProjectData.EDITING_CONTEXT_ID, diagram, ExpressionSamplesProjectData.SemanticIds.TANK_PRESSURE_LIMIT_CONSTRAINT_ID);
+        };
+
+        Consumer<Object> updatedDiagramConsumer = assertRefreshedDiagramThat(newDiagram -> {
+            new CheckDiagramElementCount(this.diagramComparator)
+                    .hasNewEdgeCount(0)
+                    // 1 node for the ConstraintUsage, 4 for its compartments (doc, attributes, constraints, ports)
+                    .hasNewNodeCount(5)
+                    .check(diagram.get(), newDiagram);
+
+            String nodeLabel = newDiagram.getNodes().get(0).getInsideLabel().getText();
+            assertThat(nodeLabel).isEqualTo("«constraint»\npressureLimit\n{ pressure <= maxPressure }");
+        });
+
+        StepVerifier.create(flux)
+                .consumeNextWith(initialDiagramContentConsumer)
+                .then(dropFromExplorerRunnable)
+                .consumeNextWith(updatedDiagramConsumer)
+                .thenCancel()
+                .verify(Duration.ofSeconds(10));
+
+    }
 
     /**
      * Executes a function in the editing context with the specified id (which is assumed to be loaded). The function

diff --git a/...m-services/src/main/java/org/eclipse/syson/diagram/services/DiagramQueryLabelService.java b/...m-services/src/main/java/org/eclipse/syson/diagram/services/DiagramQueryLabelService.java
@@ -48,6 +48,7 @@
 import org.eclipse.syson.sysml.Redefinition;
 import org.eclipse.syson.sysml.ReferenceSubsetting;
 import org.eclipse.syson.sysml.RequirementConstraintMembership;
+import org.eclipse.syson.sysml.ResultExpressionMembership;
 import org.eclipse.syson.sysml.SatisfyRequirementUsage;
 import org.eclipse.syson.sysml.StateSubactionMembership;
 import org.eclipse.syson.sysml.Subclassification;
@@ -355,12 +356,15 @@ public String getDefaultInitialDirectEditLabel(Element element) {
      * @return the label of the value part of the given {@link Usage} if there is one, an empty string otherwise.
      */
     private String getValueStringRepresentation(Usage usage, boolean directEditInput) {
+        if (directEditInput) {
+            return "";
+        }
         StringBuilder label = new StringBuilder();
         var featureValue = usage.getOwnedRelationship().stream()
                 .filter(FeatureValue.class::isInstance)
                 .map(FeatureValue.class::cast)
                 .findFirst();
-        if (featureValue.isPresent() && !directEditInput) {
+        if (featureValue.isPresent()) {
             var expression = featureValue.get().getValue();
             String valueAsString = null;
             if (expression != null) {
@@ -377,6 +381,12 @@ private String getValueStringRepresentation(Usage usage, boolean directEditInput
                     .append(this.getFeatureValueRelationshipSymbol(featureValue.get()))
                     .append(LabelConstants.SPACE)
                     .append(valueAsString);
+        } else if (usage instanceof ConstraintUsage constraintUsage) {
+            String expressionPart = this.getConstraintExpression(constraintUsage);
+            if (!expressionPart.isEmpty()) {
+                label.append(LabelConstants.CR);
+                label.append(expressionPart);
+            }
         }
         return label.toString();
     }
@@ -574,7 +584,7 @@ public String getDependencyLabel(Dependency dependency) {
      * Returns the label for the given {@link SatisfyRequirementUsage}.
      *
      * @param satisfyRequirementUsage
-     *          The given {@link SatisfyRequirementUsage}
+     *            The given {@link SatisfyRequirementUsage}
      * @return the label for the given {@link SatisfyRequirementUsage}
      */
     public String getSatisfyLabel(SatisfyRequirementUsage satisfyRequirementUsage) {
@@ -607,19 +617,35 @@ private String getCompartmentItemLabel(ConstraintUsage constraintUsage, boolean
                 label.append(this.getIdentificationLabel(constraintUsage));
                 label.append(this.getReferenceSubsettingLabel(constraintUsage));
             }
-
-            if (!directEditInput && !constraintUsage.getOwnedMember().isEmpty() && constraintUsage.getOwnedMember().get(0) instanceof Expression expression) {
-                if (!label.isEmpty()) {
-                    label.append(LabelConstants.SPACE);
-                }
-                label.append(LabelConstants.OPEN_BRACE).append(LabelConstants.SPACE);
-                label.append(this.getSysmlTextualRepresentation(expression, directEditInput));
-                label.append(LabelConstants.SPACE).append(LabelConstants.CLOSE_BRACE);
+            String expressionPart = this.getConstraintExpression(constraintUsage);
+            if (!expressionPart.isEmpty()) {
+                label.append(LabelConstants.SPACE);
+                label.append(expressionPart);
             }
         }
         return label.toString();
     }
 
+    /**
+     * Returns the string representation of the {@link Expression} associated with a {@link ConstraintUsage} using the
+     * proper syntax (between braces=.
+     *
+     * @param constraintUsage
+     *            a {@link ConstraintUsage}
+     * @param label
+     *            the string representation of the corresponding expression if it is set, or an empty string if there is
+     *            no associated expression.
+     */
+    private String getConstraintExpression(ConstraintUsage constraintUsage) {
+        StringBuilder label = new StringBuilder();
+        if (this.metamodelQueryElementService.getResultExpressionMembership(constraintUsage) instanceof ResultExpressionMembership rem && rem.getOwnedResultExpression() != null) {
+            label.append(LabelConstants.OPEN_BRACE).append(LabelConstants.SPACE);
+            label.append(this.metamodelQueryElementService.getExpressionTextualRepresentation(rem.getOwnedResultExpression()));
+            label.append(LabelConstants.SPACE).append(LabelConstants.CLOSE_BRACE);
+        }
+        return label.toString();
+    }
+
     /**
      * Return the label for the given {@link Documentation} when displayed as a compartment item.
      *