jpa-patterns

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JPA/Hibernate Patterns

JPA/Hibernate 设计模式

Use for data modeling, repositories, and performance tuning in Spring Boot.

适用于Spring Boot中的数据建模、仓库和性能调优。

Entity Design

实体设计

java

@Entity
@Table(name = "markets", indexes = {
  @Index(name = "idx_markets_slug", columnList = "slug", unique = true)
})
@EntityListeners(AuditingEntityListener.class)
public class MarketEntity {
  @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;

  @Column(nullable = false, length = 200)
  private String name;

  @Column(nullable = false, unique = true, length = 120)
  private String slug;

  @Enumerated(EnumType.STRING)
  private MarketStatus status = MarketStatus.ACTIVE;

  @CreatedDate private Instant createdAt;
  @LastModifiedDate private Instant updatedAt;
}

Enable auditing:

java

@Configuration
@EnableJpaAuditing
class JpaConfig {}

java

@Entity
@Table(name = "markets", indexes = {
  @Index(name = "idx_markets_slug", columnList = "slug", unique = true)
})
@EntityListeners(AuditingEntityListener.class)
public class MarketEntity {
  @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;

  @Column(nullable = false, length = 200)
  private String name;

  @Column(nullable = false, unique = true, length = 120)
  private String slug;

  @Enumerated(EnumType.STRING)
  private MarketStatus status = MarketStatus.ACTIVE;

  @CreatedDate private Instant createdAt;
  @LastModifiedDate private Instant updatedAt;
}

启用审计功能：

java

@Configuration
@EnableJpaAuditing
class JpaConfig {}

Relationships and N+1 Prevention

关系与N+1查询问题规避

java

@OneToMany(mappedBy = "market", cascade = CascadeType.ALL, orphanRemoval = true)
private List<PositionEntity> positions = new ArrayList<>();

Default to lazy loading; use
```
JOIN FETCH
```
in queries when needed
Avoid
```
EAGER
```
on collections; use DTO projections for read paths

java

@Query("select m from MarketEntity m left join fetch m.positions where m.id = :id")
Optional<MarketEntity> findWithPositions(@Param("id") Long id);

java

@OneToMany(mappedBy = "market", cascade = CascadeType.ALL, orphanRemoval = true)
private List<PositionEntity> positions = new ArrayList<>();

默认使用懒加载；必要时在查询中使用
```
JOIN FETCH
```
避免在集合上使用
```
EAGER
```
；读取路径使用DTO投影

java

@Query("select m from MarketEntity m left join fetch m.positions where m.id = :id")
Optional<MarketEntity> findWithPositions(@Param("id") Long id);

Repository Patterns

仓库设计模式

java

public interface MarketRepository extends JpaRepository<MarketEntity, Long> {
  Optional<MarketEntity> findBySlug(String slug);

  @Query("select m from MarketEntity m where m.status = :status")
  Page<MarketEntity> findByStatus(@Param("status") MarketStatus status, Pageable pageable);
}

Use projections for lightweight queries:

java

public interface MarketSummary {
  Long getId();
  String getName();
  MarketStatus getStatus();
}
Page<MarketSummary> findAllBy(Pageable pageable);

java

public interface MarketRepository extends JpaRepository<MarketEntity, Long> {
  Optional<MarketEntity> findBySlug(String slug);

  @Query("select m from MarketEntity m where m.status = :status")
  Page<MarketEntity> findByStatus(@Param("status") MarketStatus status, Pageable pageable);
}

使用投影实现轻量查询：

java

public interface MarketSummary {
  Long getId();
  String getName();
  MarketStatus getStatus();
}
Page<MarketSummary> findAllBy(Pageable pageable);

Transactions

事务处理

Annotate service methods with
```
@Transactional
```
Use
```
@Transactional(readOnly = true)
```
for read paths to optimize
Choose propagation carefully; avoid long-running transactions

java

@Transactional
public Market updateStatus(Long id, MarketStatus status) {
  MarketEntity entity = repo.findById(id)
      .orElseThrow(() -> new EntityNotFoundException("Market"));
  entity.setStatus(status);
  return Market.from(entity);
}

为服务方法添加
```
@Transactional
```
注解
读取路径使用
```
@Transactional(readOnly = true)
```
以优化性能
谨慎选择传播机制；避免长时间运行的事务

java

@Transactional
public Market updateStatus(Long id, MarketStatus status) {
  MarketEntity entity = repo.findById(id)
      .orElseThrow(() -> new EntityNotFoundException("Market"));
  entity.setStatus(status);
  return Market.from(entity);
}

Pagination

分页处理

java

PageRequest page = PageRequest.of(pageNumber, pageSize, Sort.by("createdAt").descending());
Page<MarketEntity> markets = repo.findByStatus(MarketStatus.ACTIVE, page);

For cursor-like pagination, include

id > :lastId

in JPQL with ordering.

java

PageRequest page = PageRequest.of(pageNumber, pageSize, Sort.by("createdAt").descending());
Page<MarketEntity> markets = repo.findByStatus(MarketStatus.ACTIVE, page);

对于类似游标分页的需求，在JPQL中结合排序添加

id > :lastId

条件。

Indexing and Performance

索引与性能优化

Add indexes for common filters (
```
status
```
,
```
slug
```
, foreign keys)
Use composite indexes matching query patterns (
```
status, created_at
```
)
Avoid
```
select *
```
; project only needed columns
Batch writes with
```
saveAll
```
and
```
hibernate.jdbc.batch_size
```

为常用筛选字段（
```
status
```
、
```
slug
```
、外键）添加索引
创建与查询模式匹配的复合索引（如
```
status, created_at
```
）
避免
```
select *
```
；仅投影所需列
使用
```
saveAll
```
和
```
hibernate.jdbc.batch_size
```
实现批量写入

Connection Pooling (HikariCP)

连接池（HikariCP）

Recommended properties:

spring.datasource.hikari.maximum-pool-size=20
spring.datasource.hikari.minimum-idle=5
spring.datasource.hikari.connection-timeout=30000
spring.datasource.hikari.validation-timeout=5000

For PostgreSQL LOB handling, add:

spring.jpa.properties.hibernate.jdbc.lob.non_contextual_creation=true

推荐配置属性：

spring.datasource.hikari.maximum-pool-size=20
spring.datasource.hikari.minimum-idle=5
spring.datasource.hikari.connection-timeout=30000
spring.datasource.hikari.validation-timeout=5000

针对PostgreSQL的LOB处理，添加：

spring.jpa.properties.hibernate.jdbc.lob.non_contextual_creation=true

Caching

缓存处理

1st-level cache is per EntityManager; avoid keeping entities across transactions
For read-heavy entities, consider second-level cache cautiously; validate eviction strategy

一级缓存基于EntityManager；避免跨事务保留实体
对于读密集型实体，谨慎考虑二级缓存；验证驱逐策略

Migrations

数据库迁移

Use Flyway or Liquibase; never rely on Hibernate auto DDL in production
Keep migrations idempotent and additive; avoid dropping columns without plan

使用Flyway或Liquibase；生产环境绝不依赖Hibernate自动DDL
保持迁移的幂等性和增量性；无计划时避免删除列

Testing Data Access

数据访问测试

Prefer
```
@DataJpaTest
```
with Testcontainers to mirror production

Assert SQL efficiency using logs: set

logging.level.org.hibernate.SQL=DEBUG

and

logging.level.org.hibernate.orm.jdbc.bind=TRACE

for parameter values

Remember: Keep entities lean, queries intentional, and transactions short. Prevent N+1 with fetch strategies and projections, and index for your read/write paths.

优先使用
```
@DataJpaTest
```
结合Testcontainers以镜像生产环境

通过日志断言SQL效率：设置

logging.level.org.hibernate.SQL=DEBUG

和

logging.level.org.hibernate.orm.jdbc.bind=TRACE

查看参数值

注意：保持实体精简，查询目标明确，事务简短。通过抓取策略和投影规避N+1问题，为读写路径创建合适的索引。