SONARJAVA-6537 Implement rule S8948: "@OneToMany" relationships should use "mappedBy" or "@JoinColumn"

its/autoscan/src/test/resources/autoscan/diffs/diff_S8948.json

@@ -0,0 +1,6 @@
+{
+  "ruleKey": "S8948",
+  "hasTruePositives": false,
+  "falseNegatives": 8,
+  "falsePositives": 0
+}

java-checks-test-sources/default/src/main/java/checks/OneToManyMappingCheckSample.java

@@ -0,0 +1,61 @@
+package checks;
+
+import jakarta.persistence.Entity;
+import jakarta.persistence.JoinColumn;
+import jakarta.persistence.ManyToOne;
+import jakarta.persistence.OneToMany;
+import java.util.List;
+
+public class OneToManyMappingCheckSample {
+
+  @Entity
+  class Author {
+    @OneToMany // Noncompliant {{Add "mappedBy" or "@JoinColumn" to this "@OneToMany" relationship.}}
+//  ^^^^^^^^^^
+    private List<Book> books;
+  }
+
+  @Entity
+  class Book {
+    @ManyToOne
+    private Author author;
+  }
+
+  // Compliant: uses mappedBy
+  @Entity
+  class AuthorWithMappedBy {
+    @OneToMany(mappedBy = "author")
+    private List<BookWithAuthor> books;
+  }
+
+  @Entity
+  class BookWithAuthor {
+    @ManyToOne
+    @JoinColumn(name = "author_id")
+    private AuthorWithMappedBy author;
+  }
+
+  // Compliant: uses @JoinColumn on the @OneToMany field
+  @Entity
+  class AuthorWithJoinColumn {
+    @OneToMany
+    @JoinColumn(name = "author_id")
+    private List<BookNoRef> books;
+  }
+
+  @Entity
+  class BookNoRef {
+    // No reference back to Author
+  }
+
+  @Entity
+  class AuthorUnidirectional {
+    @OneToMany // Noncompliant
+    private List<AnotherBook> books;
+  }
+
+  @Entity
+  class AnotherBook {
+    // No reference back
+  }
+}

java-checks-test-sources/default/src/main/java/checks/OneToManyMappingCheckSampleJavax.java

@@ -0,0 +1,61 @@
+package checks;
+
+import java.util.List;
+import javax.persistence.Entity;
+import javax.persistence.JoinColumn;
+import javax.persistence.ManyToOne;
+import javax.persistence.OneToMany;
+
+public class OneToManyMappingCheckSampleJavax {
+
+  @Entity
+  class Author {
+    @OneToMany // Noncompliant {{Add "mappedBy" or "@JoinColumn" to this "@OneToMany" relationship.}}
+//  ^^^^^^^^^^
+    private List<Book> books;
+  }
+
+  @Entity
+  class Book {
+    @ManyToOne
+    private Author author;
+  }
+
+  // Compliant: uses mappedBy
+  @Entity
+  class AuthorWithMappedBy {
+    @OneToMany(mappedBy = "author")
+    private List<BookWithAuthor> books;
+  }
+
+  @Entity
+  class BookWithAuthor {
+    @ManyToOne
+    @JoinColumn(name = "author_id")
+    private AuthorWithMappedBy author;
+  }
+
+  // Compliant: uses @JoinColumn on the @OneToMany field
+  @Entity
+  class AuthorWithJoinColumn {
+    @OneToMany
+    @JoinColumn(name = "author_id")
+    private List<BookNoRef> books;
+  }
+
+  @Entity
+  class BookNoRef {
+    // No reference back to Author
+  }
+
+  @Entity
+  class AuthorUnidirectional {
+    @OneToMany // Noncompliant
+    private List<AnotherBook> books;
+  }
+
+  @Entity
+  class AnotherBook {
+    // No reference back
+  }
+}

java-checks/src/main/java/org/sonar/java/checks/OneToManyMappingCheck.java

@@ -0,0 +1,74 @@
+/*
+ * SonarQube Java
+ * Copyright (C) SonarSource Sàrl
+ * mailto:info AT sonarsource DOT com
+ *
+ * You can redistribute and/or modify this program under the terms of
+ * the Sonar Source-Available License Version 1, as published by SonarSource Sàrl.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the Sonar Source-Available License for more details.
+ *
+ * You should have received a copy of the Sonar Source-Available License
+ * along with this program; if not, see https://sonarsource.com/license/ssal/
+ */
+package org.sonar.java.checks;
+
+import java.util.List;
+import java.util.Set;
+import org.sonar.check.Rule;
+import org.sonar.plugins.java.api.IssuableSubscriptionVisitor;
+import org.sonar.plugins.java.api.tree.AnnotationTree;
+import org.sonar.plugins.java.api.tree.AssignmentExpressionTree;
+import org.sonar.plugins.java.api.tree.IdentifierTree;
+import org.sonar.plugins.java.api.tree.Tree;
+import org.sonar.plugins.java.api.tree.VariableTree;
+
+@Rule(key = "S8948")
+public class OneToManyMappingCheck extends IssuableSubscriptionVisitor {
+
+  private static final Set<String> ONE_TO_MANY_ANNOTATIONS = Set.of(
+    "jakarta.persistence.OneToMany",
+    "javax.persistence.OneToMany");
+
+  private static final Set<String> JOIN_COLUMN_ANNOTATIONS = Set.of(
+    "jakarta.persistence.JoinColumn",
+    "javax.persistence.JoinColumn");
+
+  @Override
+  public List<Tree.Kind> nodesToVisit() {
+    return List.of(Tree.Kind.VARIABLE);
+  }
+
+  @Override
+  public void visitNode(Tree tree) {
+    var variable = (VariableTree) tree;
+    var annotations = variable.modifiers().annotations();
+
+    annotations.stream()
+      .filter(OneToManyMappingCheck::isOneToManyAnnotation)
+      .filter(annotation -> !hasMappedBy(annotation))
+      .filter(annotation -> annotations.stream().noneMatch(OneToManyMappingCheck::isJoinColumnAnnotation))
+      .forEach(annotation -> reportIssue(annotation, "Add \"mappedBy\" or \"@JoinColumn\" to this \"@OneToMany\" relationship."));
+  }
+
+  private static boolean isOneToManyAnnotation(AnnotationTree annotation) {
+    return ONE_TO_MANY_ANNOTATIONS.stream().anyMatch(annotation.annotationType().symbolType()::is);
+  }
+
+  private static boolean isJoinColumnAnnotation(AnnotationTree annotation) {
+    return JOIN_COLUMN_ANNOTATIONS.stream().anyMatch(annotation.annotationType().symbolType()::is);
+  }
+
+  private static boolean hasMappedBy(AnnotationTree annotation) {
+    return annotation.arguments().stream()
+      .filter(arg -> arg.is(Tree.Kind.ASSIGNMENT))
+      .map(AssignmentExpressionTree.class::cast)
+      .map(AssignmentExpressionTree::variable)
+      .filter(v -> v.is(Tree.Kind.IDENTIFIER))
+      .map(IdentifierTree.class::cast)
+      .anyMatch(id -> "mappedBy".equals(id.name()));
+  }
+}

java-checks/src/test/java/org/sonar/java/checks/OneToManyMappingCheckTest.java

@@ -0,0 +1,41 @@
+/*
+ * SonarQube Java
+ * Copyright (C) SonarSource Sàrl
+ * mailto:info AT sonarsource DOT com
+ *
+ * You can redistribute and/or modify this program under the terms of
+ * the Sonar Source-Available License Version 1, as published by SonarSource Sàrl.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the Sonar Source-Available License for more details.
+ *
+ * You should have received a copy of the Sonar Source-Available License
+ * along with this program; if not, see https://sonarsource.com/license/ssal/
+ */
+package org.sonar.java.checks;
+
+import org.junit.jupiter.api.Test;
+import org.sonar.java.checks.verifier.CheckVerifier;
+
+import static org.sonar.java.checks.verifier.TestUtils.mainCodeSourcesPath;
+
+class OneToManyMappingCheckTest {
+
+  @Test
+  void testJakarta() {
+    CheckVerifier.newVerifier()
+      .onFile(mainCodeSourcesPath("checks/OneToManyMappingCheckSample.java"))
+      .withCheck(new OneToManyMappingCheck())
+      .verifyIssues();
+  }
+
+  @Test
+  void testJavax() {
+    CheckVerifier.newVerifier()
+      .onFile(mainCodeSourcesPath("checks/OneToManyMappingCheckSampleJavax.java"))
+      .withCheck(new OneToManyMappingCheck())
+      .verifyIssues();
+  }
+}

sonar-java-plugin/src/main/resources/org/sonar/l10n/java/rules/java/S8948.html

@@ -0,0 +1,104 @@
+<p>This is an issue when a one-to-many relationship in object-relational mapping is declared without either specifying which side owns the
+bidirectional relationship or providing explicit foreign key column configuration, causing the ORM framework to create an unnecessary join table.</p>
+<p>In JPA, this specifically refers to the <code>@OneToMany</code> annotation without a <code>mappedBy</code> attribute or <code>@JoinColumn</code>
+annotation.</p>
+<h2>Why is this an issue?</h2>
+<p>When you define a one-to-many relationship in an object-relational mapping framework without specifying how the relationship should be mapped, the
+persistence provider follows its specification default: it creates a separate join table to represent the association.</p>
+<p>For example, if you have an <code>Author</code> entity with a collection of <code>Book</code> entities:</p>
+<pre>
+Entity: Author
+  one-to-many relationship -&gt; books: collection of Book
+</pre>
+<p>The ORM will create three tables: <code>Author</code>, <code>Book</code>, and <code>Author_Book</code> (the join table). The join table contains
+two foreign key columns: one referencing <code>Author</code> and one referencing <code>Book</code>.</p>
+<p>This default behavior is rarely what you want for true one-to-many relationships</p>
+<p>In JPA, this occurs when you use the <code>@OneToMany</code> annotation without additional mapping configuration. For example:</p>
+<pre>
+@Entity
+public class Author {
+    @OneToMany
+    private List&lt;Book&gt; books;
+}
+</pre>
+<h3>What is the potential impact?</h3>
+<p>Using the default join table mapping for one-to-many relationships in object-relational mapping frameworks degrades application performance through
+additional database tables, extra SQL statements, and more complex query plans. It also makes the database schema less intuitive and harder to
+maintain, as the foreign key is not stored where developers would naturally expect it.</p>
+<p>In Java, this specifically refers to the <code>@OneToMany</code> annotation in JPA (Java Persistence API) and Hibernate.</p>
+<h2>How to fix it</h2>
+<p>For bidirectional relationships (where the child entity has a reference back to the parent), use the <code>mappedBy</code> attribute on the
+<code>@OneToMany</code> side to indicate that the relationship is owned by the child entity. This tells JPA to use the foreign key column on the child
+table. The <code>mappedBy</code> value must match the field name in the child entity that references the parent.</p>
+<p>For unidirectional relationships (where only the parent knows about the children), use <code>@JoinColumn</code> to specify that the foreign key
+should be stored in the child table. The <code>@JoinColumn</code> annotation tells JPA to create or use a foreign key column in the child table
+instead of creating a join table.</p>
+<h3>Code examples</h3>
+<h4>Noncompliant code example</h4>
+<pre data-diff-id="1" data-diff-type="noncompliant">
+@Entity
+public class Author {
+    @OneToMany // Noncompliant
+    private List&lt;Book&gt; books;
+}
+
+@Entity
+public class Book {
+    @ManyToOne
+    private Author author;
+}
+</pre>
+<h4>Compliant solution</h4>
+<pre data-diff-id="1" data-diff-type="compliant">
+@Entity
+public class Author {
+    @OneToMany(mappedBy = "author")
+    private List&lt;Book&gt; books;
+}
+
+@Entity
+public class Book {
+    @ManyToOne
+    @JoinColumn(name = "author_id")
+    private Author author;
+}
+</pre>
+<h4>Noncompliant code example</h4>
+<pre data-diff-id="2" data-diff-type="noncompliant">
+@Entity
+public class Author {
+    @OneToMany // Noncompliant
+    private List&lt;Book&gt; books;
+}
+
+@Entity
+public class Book {
+    // No reference back to Author
+}
+</pre>
+<h4>Compliant solution</h4>
+<pre data-diff-id="2" data-diff-type="compliant">
+@Entity
+public class Author {
+    @OneToMany
+    @JoinColumn(name = "author_id")
+    private List&lt;Book&gt; books;
+}
+
+@Entity
+public class Book {
+    // No reference back to Author
+    // JPA will add author_id column to Book table
+}
+</pre>
+<h2>Resources</h2>
+<h3>Documentation</h3>
+<ul>
+  <li>Jakarta Persistence Specification - <a
+  href="https://jakarta.ee/specifications/persistence/3.1/jakarta-persistence-spec-3.1.html#a538">Relationship Mapping Defaults</a></li>
+  <li>Hibernate documentation - <a
+  href="https://docs.jboss.org/hibernate/orm/6.2/userguide/html_single/Hibernate_User_Guide.html#associations">Hibernate ORM User Guide -
+  Associations</a></li>
+  <li>Baeldung - <a href="https://www.baeldung.com/jpa-hibernate-associations">Understanding JPA/Hibernate Associations</a></li>
+</ul>
+

sonar-java-plugin/src/main/resources/org/sonar/l10n/java/rules/java/S8948.json

@@ -0,0 +1,26 @@
+{
+  "title": "\"@OneToMany\" relationships should use \"mappedBy\" or \"@JoinColumn\"",
+  "type": "CODE_SMELL",
+  "status": "ready",
+  "remediation": {
+    "func": "Constant\/Issue",
+    "constantCost": "5 min"
+  },
+  "tags": [
+    "jpa",
+    "hibernate",
+    "performance",
+    "jakarta"
+  ],
+  "defaultSeverity": "Major",
+  "ruleSpecification": "RSPEC-8948",
+  "sqKey": "S8948",
+  "scope": "All",
+  "quickfix": "unknown",
+  "code": {
+    "impacts": {
+      "MAINTAINABILITY": "MEDIUM"
+    },
+    "attribute": "EFFICIENT"
+  }
+}

sonar-java-plugin/src/main/resources/org/sonar/l10n/java/rules/java/Sonar_way_profile.json

@@ -535,6 +535,7 @@
     "S8745",
     "S8786",
     "S8911",
-    "S8924"
+    "S8924",
+    "S8948"
   ]
 }