Add Hibernate 7 batches 2-6, batch 7, and batch 8: mapping styles, JPA annotations, natural IDs, @Immutable, stored procedures, in-memory test databases, JNDI mocking, proxies, associations, temporal mapping, named queries, HQL, Criteria API, EntityManager bootstrapping, Ehcache 3 L2 cache configuration, HikariCP connection pooling, Hibernate Validator CDI integration, aggregate functions, sorting, pagination, interceptors, and Hibernate Search 8 (Hibernate 7.4.5.Final + Spring Boot 4.1.1 + JDK 25)

src/main/java/com/ankurm/hibernatedemo/naturalid/Department.java

@@ -0,0 +1,58 @@
+package com.ankurm.hibernatedemo.naturalid;
+
+import jakarta.persistence.Entity;
+import jakarta.persistence.GeneratedValue;
+import jakarta.persistence.Id;
+import jakarta.persistence.JoinColumn;
+import jakarta.persistence.ManyToOne;
+import org.hibernate.annotations.NaturalId;
+
+/**
+ * A COMPOSITE natural id: (company, deptCode) together must be unique, not either field alone.
+ * Matches the article's example -- verified to actually load via
+ * {@code session.byNaturalId(Department.class).using(...).using(...).load()}.
+ *
+ * <p>Docs: docs/06-natural-ids.md, Topic 3.
+ */
+@Entity
+public class Department {
+
+    @Id
+    @GeneratedValue
+    private Long id;
+
+    @NaturalId
+    @ManyToOne
+    @JoinColumn(name = "company_id")
+    private Company company;
+
+    @NaturalId
+    private String deptCode;
+
+    private String name;
+
+    public Department() {
+    }
+
+    public Department(Company company, String deptCode, String name) {
+        this.company = company;
+        this.deptCode = deptCode;
+        this.name = name;
+    }
+
+    public Long getId() {
+        return id;
+    }
+
+    public Company getCompany() {
+        return company;
+    }
+
+    public String getDeptCode() {
+        return deptCode;
+    }
+
+    public String getName() {
+        return name;
+    }
+}