fix(ontology): cardinality of one can be added to classes as long as …

…not used in data (#1958)

* allow adding cardinalities of 1 if class not used in data

* Adjust e2e test

* Update ontology-information.md

* fix indentations ins ScalaDoc

Co-authored-by: Ivan Subotic <400790+subotic@users.noreply.github.com>

docs/03-apis/api-v2/ontology-information.md

@@ -1452,8 +1452,7 @@ the property definition, submit the request without those predicates.
 
 ### Adding Cardinalities to a Class
 
-If the class is used in data or if it
-has a subclass, it is not allowed to add cardinalities `owl:minCardinality` greater than 0 or `owl:cardinality 1` to the class.
+If the class (or any of its sub-classes) is used in data, it is not allowed to add cardinalities `owl:minCardinality` greater than 0 or `owl:cardinality 1` to the class.
 
 ```
 HTTP POST to http://host/v2/ontologies/cardinalities

webapi/src/main/scala/org/knora/webapi/responders/Responder.scala

@@ -131,6 +131,31 @@ abstract class Responder(responderData: ResponderData) extends LazyLogging {
 
     } yield isEntityUsedResponse.results.bindings.nonEmpty
 
+  /**
+   * Checks whether an instance of a class (or any ob its sub-classes) exists
+   *
+   * @param classIri  the IRI of the class.
+   *
+   * @return `true` if the class is used.
+   */
+  protected def isClassUsedInData(
+    classIri: SmartIri
+  ): Future[Boolean] =
+    for {
+      isClassUsedInDataSparql <- Future(
+        org.knora.webapi.messages.twirl.queries.sparql.v2.txt
+          .isClassUsedInData(
+            triplestore = settings.triplestoreType,
+            classIri = classIri
+          )
+          .toString()
+      )
+
+      isClassUsedInDataResponse: SparqlSelectResult <- (storeManager ? SparqlSelectRequest(isClassUsedInDataSparql))
+        .mapTo[SparqlSelectResult]
+
+    } yield isClassUsedInDataResponse.results.bindings.nonEmpty
+
   /**
    * Throws an exception if an entity is used in the triplestore.
    *
@@ -153,6 +178,24 @@ abstract class Responder(responderData: ResponderData) extends LazyLogging {
       }
     } yield ()
 
+  /**
+   * Throws an exception if a class is used in data.
+   *
+   * @param classIri  the IRI of the class.
+   * @param errorFun  a function that throws an exception. It will be called if the class is used.
+   */
+  protected def throwIfClassIsUsedInData(
+    classIri: SmartIri,
+    errorFun: => Nothing
+  ): Future[Unit] =
+    for {
+      classIsUsed: Boolean <- isClassUsedInData(classIri)
+
+      _ = if (classIsUsed) {
+        errorFun
+      }
+    } yield ()
+
   /**
    * Checks whether an entity with the provided custom IRI exists in the triplestore, if yes, throws an exception.
    * If no custom IRI was given, creates a random unused IRI.

webapi/src/main/scala/org/knora/webapi/responders/v2/OntologyResponderV2.scala

@@ -1348,15 +1348,13 @@ class OntologyResponderV2(responderData: ResponderData) extends Responder(respon
           }
 
         _ <- hasCardinality match {
-          // If there is, check that the class isn't used in data, and that it has no subclasses.
+          // If there is, check that the class isn't used in data.
           case Some((propIri: SmartIri, cardinality: KnoraCardinalityInfo)) =>
-            throwIfEntityIsUsed(
-              entityIri = internalClassIri,
+            throwIfClassIsUsedInData(
+              classIri = internalClassIri,
               errorFun = throw BadRequestException(
-                s"Cardinality ${cardinality.toString} for $propIri cannot be added to class ${addCardinalitiesRequest.classInfoContent.classIri}, because it is used in data or has a subclass"
-              ),
-              ignoreKnoraConstraints =
-                true // It's OK if a property refers to the class via knora-base:subjectClassConstraint or knora-base:objectClassConstraint.
+                s"Cardinality ${cardinality.toString} for $propIri cannot be added to class ${addCardinalitiesRequest.classInfoContent.classIri}, because it is used in data"
+              )
             )
           case None => Future.successful(())
         }

webapi/src/main/twirl/org/knora/webapi/messages/twirl/queries/sparql/v2/isClassUsedInData.scala.txt

@@ -0,0 +1,33 @@
+@*
+ * Copyright © 2021 Data and Service Center for the Humanities and/or DaSCH Service Platform contributors.
+ * SPDX-License-Identifier: Apache-2.0
+ *@
+
+@import org.knora.webapi.messages.SmartIri
+
+@*
+ * Checks if an instance of a class exists (if yes, that means the class is used in data)
+ *
+ * @param triplestore the name of the triplestore being used.
+ * @param classIri the IRI of the class.
+ *@
+@(triplestore: String,
+  classIri: SmartIri)
+
+PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
+PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
+
+SELECT DISTINCT ?isUsed
+
+WHERE {
+    BIND(IRI("@classIri") AS ?class)
+    BIND(true AS ?isUsed)
+
+    {
+      ?resourceInstance rdf:type ?class
+    }
+    UNION{
+      ?subClass rdfs:subClassOf* ?class .
+      ?resourceInstance rdf:type ?subClass
+    }
+}

webapi/src/test/scala/org/knora/webapi/responders/v2/OntologyResponderV2Spec.scala

@@ -3480,7 +3480,7 @@ class OntologyResponderV2Spec extends CoreSpec() with ImplicitSender {
       }
     }
 
-    "not add a cardinality=1 to the class anything:Nothing, because it has a subclass" in {
+    "add a cardinality=1 to the class anything:Nothing which has a subclass" in {
       val classIri = AnythingOntologyIri.makeEntityIri("Nothing")
 
       val classInfoContent = ClassInfoContentV2(
@@ -3505,9 +3505,34 @@ class OntologyResponderV2Spec extends CoreSpec() with ImplicitSender {
         requestingUser = anythingAdminUser
       )
 
-      expectMsgPF(timeout) { case msg: akka.actor.Status.Failure =>
-        if (printErrorMessages) println(msg.cause.getMessage)
-        msg.cause.isInstanceOf[BadRequestException] should ===(true)
+      expectMsgPF(timeout) { case msg: ReadOntologyV2 =>
+        val externalOntology = msg.toOntologySchema(ApiV2Complex)
+        assert(externalOntology.classes.size == 1)
+
+        val metadata = externalOntology.ontologyMetadata
+        val newAnythingLastModDate = metadata.lastModificationDate.getOrElse(
+          throw AssertionException(s"${metadata.ontologyIri} has no last modification date")
+        )
+        assert(newAnythingLastModDate.isAfter(anythingLastModDate))
+        anythingLastModDate = newAnythingLastModDate
+      }
+
+      responderManager ! DeleteCardinalitiesFromClassRequestV2(
+        classInfoContent = classInfoContent,
+        lastModificationDate = anythingLastModDate,
+        apiRequestID = UUID.randomUUID,
+        featureFactoryConfig = defaultFeatureFactoryConfig,
+        requestingUser = anythingAdminUser
+      )
+
+      expectMsgPF(timeout) { case msg: ReadOntologyV2 =>
+        val externalOntology = msg.toOntologySchema(ApiV2Complex)
+        val metadata = externalOntology.ontologyMetadata
+        val newAnythingLastModDate = metadata.lastModificationDate.getOrElse(
+          throw AssertionException(s"${metadata.ontologyIri} has no last modification date")
+        )
+        assert(newAnythingLastModDate.isAfter(anythingLastModDate))
+        anythingLastModDate = newAnythingLastModDate
       }
     }