Add AuthorRepository.java

src/main/java/com/ankurm/sdjpa4demo/repo/AuthorRepository.java

@@ -0,0 +1,45 @@
+package com.ankurm.sdjpa4demo.repo;
+
+import com.ankurm.sdjpa4demo.domain.Author;
+import org.jspecify.annotations.Nullable;
+import org.springframework.data.domain.Sort;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.JpaSpecificationExecutor;
+import org.springframework.data.jpa.repository.Modifying;
+import org.springframework.data.jpa.repository.Query;
+import org.springframework.data.repository.query.Param;
+import org.springframework.transaction.annotation.Transactional;
+
+import java.util.List;
+import java.util.Optional;
+
+public interface AuthorRepository
+        extends JpaRepository<Author, Long>, JpaSpecificationExecutor<Author> {
+
+    // (1) Optional single result -> empty when not found (never throws for "not found").
+    Optional<Author> findByName(String name);
+
+    // (2) Non-null single result. In a @NullMarked package this is the DEFAULT.
+    //     Missing row -> EmptyResultDataAccessException. Null argument -> IllegalArgumentException.
+    Author getByName(String name);
+
+    // (3) Explicitly @Nullable single result -> returns null when not found,
+    //     and tolerates a null argument.
+    @Nullable
+    Author findByCountry(@Nullable String country);
+
+    // (4) Derived query used to demonstrate the Criteria -> JPQL shift (watch the SQL log).
+    List<Author> findByNameStartingWithOrderByNameAsc(String prefix);
+
+    // (5) Sort with explicit NULLS precedence. Consistent for derived queries in SD JPA 4.
+    List<Author> findByNameStartingWith(String prefix, Sort sort);
+
+    // (6) New JPA 3.2 / Hibernate 7 JPQL features: || concatenation + replace() function.
+    @Query("select replace(a.name, ' ', '_') || ':' || coalesce(a.country, 'N/A') from Author a where a.id = :id")
+    String badgeFor(@Param("id") Long id);
+
+    // (7) Derived DELETE returning the affected count.
+    @Modifying
+    @Transactional
+    long deleteByCountry(@Nullable String country);
+}