Java Architect

# JPA Optimization

## Optimized Entity Design

```java
package com.example.domain.model;

import jakarta.persistence.*;
import lombok.*;
import org.hibernate.annotations.BatchSize;
import org.hibernate.annotations.Cache;
import org.hibernate.annotations.CacheConcurrencyStrategy;
import org.springframework.data.annotation.CreatedDate;
import org.springframework.data.annotation.LastModifiedDate;
import org.springframework.data.jpa.domain.support.AuditingEntityListener;

import java.time.Instant;
import java.util.ArrayList;
import java.util.List;

@Entity
@Table(
    name = "users",
    indexes = {
        @Index(name = "idx_email", columnList = "email"),
        @Index(name = "idx_created_at", columnList = "created_at")
    }
)
@EntityListeners(AuditingEntityListener.class)
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@Builder
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false, unique = true, length = 100)
    private String email;

    @Column(nullable = false, length = 50)
    private String username;

    @Column(nullable = false)
    private Boolean active = true;

    @OneToMany(
        mappedBy = "user",
        cascade = CascadeType.ALL,
        orphanRemoval = true,
        fetch = FetchType.LAZY
    )
    @BatchSize(size = 25)
    @Builder.Default
    private List<Order> orders = new ArrayList<>();

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "department_id")
    private Department department;

    @CreatedDate
    @Column(nullable = false, updatable = false)
    private Instant createdAt;

    @LastModifiedDate
    private Instant updatedAt;

    @Version
    private Long version;

    // Helper methods
    public void addOrder(Order order) {
        orders.add(order);
        order.setUser(this);
    }

    public void removeOrder(Order order) {
        orders.remove(order);
        order.setUser(null);
    }
}
```

## Repository with Custom Queries

```java
package com.example.domain.repository;

import com.example.domain.model.User;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.jpa.repository.EntityGraph;
import org.springframework.data.jpa.repository.Modifying;
import org.springframework.data.repository.query.Param;

import java.time.Instant;
import java.util.List;
import java.util.Optional;

public interface UserRepository extends JpaRepository<User, Long> {

    // N+1 prevention with EntityGraph
    @EntityGraph(attributePaths = {"orders", "department"})
    @Query("SELECT u FROM User u WHERE u.id = :id")
    Optional<User> findByIdWithOrders(@Param("id") Long id);

    // Projection for read-only queries
    @Query("""
        SELECT new com.example.application.dto.UserSummary(
            u.id, u.email, u.username, COUNT(o)
        )
        FROM User u
        LEFT JOIN u.orders o
        WHERE u.active = true
        GROUP BY u.id, u.email, u.username
        """)
    List<UserSummary> findActiveUsersSummary();

    // Fetch join to avoid N+1
    @Query("""
        SELECT DISTINCT u FROM User u
        LEFT JOIN FETCH u.orders
        WHERE u.department.id = :deptId
        """)
    List<User> findByDepartmentWithOrders(@Param("deptId") Long deptId);

    // Pagination with count query optimization
    @Query(
        value = "SELECT u FROM User u WHERE u.active = true",
        countQuery = "SELECT COUNT(u) FROM User u WHERE u.active = true"
    )
    Page<User> findActiveUsers(Pageable pageable);

    // Batch update
    @Modifying
    @Query("UPDATE User u SET u.active = false WHERE u.createdAt < :date")
    int deactivateOldUsers(@Param("date") Instant date);

    // Native query for complex operations
    @Query(
        value = """
            SE