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Spring-Data-Jpa使用总结

由 冷暖自知 提交于 2019-12-01 15:12:36

参考资源列表

  1. 官方文档：https://docs.spring.io/spring-data/jpa/docs/2.1.5.RELEASE/reference/html/
  2. 《Spring Data JPA入门到精通》

前言

JPA是Java Persistence API的简称，是Spring在Hibernate的基础上进行的二次封装框架，为了更好更方便的融入Spring大家庭，同时也提供了一些Hibernate没有的特性，与其他ORM框架一起构成SpringData，统一封装了ORM层，使开发人员使用起来更加方便快捷。

备注：本文所有代码都是基于SpringBoot 2.1.5版本

JPA的使用

基本单表操作的使用

对于操作单表来说，jpa提供了非常方便使用的封装，我们只需要按规范编写Repository接口同时继承JpaRepository就可以享用jpa基本功能了。代码如下：

User实体:

package com.yizhu.entity;  import lombok.Builder; import lombok.Data; import lombok.ToString;  import javax.persistence.*; import java.io.Serializable; import java.util.List; import java.util.Set;  @Entity @Table(name = "t_user") @Data @Builder public class User implements Serializable {      private static final long serialVersionUID = 1L;      @Id     @GeneratedValue(strategy = GenerationType.IDENTITY)     private Long id;      private String name;      private String password;      private Integer age;      private Integer sex; }

repository接口：

package com.yizhu.repository;  import com.yizhu.entity.User;  public interface UserRepository extends JpaRepository<User, Long>{ }

下面看看jpa为我们提供了哪些默认操作单表数据的方法

package org.springframework.data.jpa.repository; @NoRepositoryBean public interface JpaRepository<T, ID> extends PagingAndSortingRepository<T, ID>, QueryByExampleExecutor<T> {     List<T> findAll(); // 查询全表数据      List<T> findAll(Sort var1); // 查询全表数据，支持排序      List<T> findAllById(Iterable<ID> var1); // 根据id字段查询所有匹配数据      <S extends T> List<S> saveAll(Iterable<S> var1); // 批量保存或更新数据      void flush(); // 刷新本地缓存到数据库      <S extends T> S saveAndFlush(S var1); // 保存或更新单挑数据及刷新本地缓存到数据库      void deleteInBatch(Iterable<T> var1); // 批量删除数据      void deleteAllInBatch(); // 批量删除全表数据      T getOne(ID var1); // 根据id查询一条匹配数据      <S extends T> List<S> findAll(Example<S> ar1); // Example方式的查询指定实体      <S extends T> List<S> findAll(Example<S> var1, Sort var2);  // Example方式的查询指定实体并排序 }
package org.springframework.data.repository; @NoRepositoryBean public interface PagingAndSortingRepository<T, ID> extends CrudRepository<T, ID> {     Iterable<T> findAll(Sort var1);  // 根据排序查询全表，返回类型是任意集合      Page<T> findAll(Pageable var1); // 根据分页参数分页查询 }
package org.springframework.data.repository; @NoRepositoryBean public interface CrudRepository<T, ID> extends Repository<T, ID> {     <S extends T> S save(S var1);   // 保存或更新单条数据      <S extends T> Iterable<S> saveAll(Iterable<S> var1);  // 批量保存或更新      Optional<T> findById(ID var1);  // 根据id查询数据，返回类型是Optional      boolean existsById(ID var1);    // 根据id判断数据是否存在      Iterable<T> findAll(); // 查询全表数据，返回类型为集合      Iterable<T> findAllById(Iterable<ID> var1); // 根据id集合查询数据      long count();   // 统计全表数据量      void deleteById(ID var1); // 根据id删除数据      void delete(T var1);    // 删除单条数据      void deleteAll(Iterable<? extends T> var1);     // 删除指定集合数据      void deleteAll();   // 删除全表数据 }
package org.springframework.data.repository.query; public interface QueryByExampleExecutor<T> {     <S extends T> Optional<S> findOne(Example<S> var1); // 根据Example查询一条      <S extends T> Iterable<S> findAll(Example<S> var1); // 根据Example查询所有数据      <S extends T> Iterable<S> findAll(Example<S> var1, Sort var2);  // 根据Example查询所有数据，并排序      <S extends T> Page<S> findAll(Example<S> var1, Pageable var2);  // 根据Example分页查询      <S extends T> long count(Example<S> var1);  // 根据Example统计      <S extends T> boolean exists(Example<S> var1);  // 根据Example判断数据是否存在 }

除此之外，jpa提供了一套新的生成sql的机制，非常方便好用，jpa根据Repository接口的方法中的关键字、实体字段及出入参，自动生成sql，这种方式启动容器的时候就可以检查语法是否正确，简单使用例子如下：

package com.yizhu.repository;  import com.yizhu .entity.User; import org.springframework.data.jpa.repository.EntityGraph; import org.springframework.data.jpa.repository.JpaRepository; import org.springframework.data.jpa.repository.JpaSpecificationExecutor; import org.springframework.data.jpa.repository.Query; import org.springframework.data.repository.query.Param;  import java.util.List;  public interface UserRepository extends JpaRepository<User, Long>{      /**      * 根据年龄查询用户信息      * @param age      * @return      */     List<User> findAllByAge(Integer age);      /**      * 根据用户性别和所属组织名称查询用户信息      * @param userSex      * @param orgName      * @return      */     List<User> findBySexAndOrg(@Param("sex") Integer sex, @Param("name") String name);      /**      * 根据用户名模糊查询      * @return      */     List<User> findAllByNameLike(@Param("name") String name); }

除了find 、By、And之外，还有一些关键词，全部定义在PartTree、Part类，组装起来可以生成各种各样的sql，下面截取部分代码，感兴趣的同学可以打开源码去阅读

package org.springframework.data.repository.query.parser; public class PartTree implements Streamable<PartTree.OrPart> {     private static final String KEYWORD_TEMPLATE = "(%s)(?=(\\p{Lu}|\\P{InBASIC_LATIN}))";     private static final String QUERY_PATTERN = "find|read|get|query|stream";     private static final String COUNT_PATTERN = "count";     private static final String EXISTS_PATTERN = "exists";     private static final String DELETE_PATTERN = "delete|remove";     private static final Pattern PREFIX_TEMPLATE = Pattern.compile("^(find|read|get|query|stream|count|exists|delete|remove)((\\p{Lu}.*?))??By");     private final PartTree.Subject subject;     private final PartTree.Predicate predicate;     ...     private static String[] split(String text, String keyword) {         Pattern pattern = Pattern.compile(String.format("(%s)(?=(\\p{Lu}|\\P{InBASIC_LATIN}))", keyword));         return pattern.split(text);     }      private static class Predicate implements Streamable<PartTree.OrPart> {         private static final Pattern ALL_IGNORE_CASE = Pattern.compile("AllIgnor(ing|e)Case");         private static final String ORDER_BY = "OrderBy";         private final List<PartTree.OrPart> nodes;         private final OrderBySource orderBySource;         private boolean alwaysIgnoreCase;          public Predicate(String predicate, Class<?> domainClass) {             String[] parts = PartTree.split(this.detectAndSetAllIgnoreCase(predicate), "OrderBy");             if (parts.length > 2) {                 throw new IllegalArgumentException("OrderBy must not be used more than once in a method name!");             } else {                 this.nodes = (List)Arrays.stream(PartTree.split(parts[0], "Or")).filter(StringUtils::hasText).map((part) -> {                     return new PartTree.OrPart(part, domainClass, this.alwaysIgnoreCase);                 }).collect(Collectors.toList());                 this.orderBySource = parts.length == 2 ? new OrderBySource(parts[1], Optional.of(domainClass)) : OrderBySource.EMPTY;             }         }         ...     }      private static class Subject {         private static final String DISTINCT = "Distinct";         private static final Pattern COUNT_BY_TEMPLATE = Pattern.compile("^count(\\p{Lu}.*?)??By");         private static final Pattern EXISTS_BY_TEMPLATE = Pattern.compile("^(exists)(\\p{Lu}.*?)??By");         private static final Pattern DELETE_BY_TEMPLATE = Pattern.compile("^(delete|remove)(\\p{Lu}.*?)??By");         private static final String LIMITING_QUERY_PATTERN = "(First|Top)(\\d*)?";         private static final Pattern LIMITED_QUERY_TEMPLATE = Pattern.compile("^(find|read|get|query|stream)(Distinct)?(First|Top)(\\d*)?(\\p{Lu}.*?)??By");         private final boolean distinct;         private final boolean count;         private final boolean exists;         private final boolean delete;         private final Optional<Integer> maxResults;          public Subject(Optional<String> subject) {             this.distinct = (Boolean)subject.map((it) -> {                 return it.contains("Distinct");             }).orElse(false);             this.count = this.matches(subject, COUNT_BY_TEMPLATE);             this.exists = this.matches(subject, EXISTS_BY_TEMPLATE);             this.delete = this.matches(subject, DELETE_BY_TEMPLATE);             this.maxResults = this.returnMaxResultsIfFirstKSubjectOrNull(subject);         }          private Optional<Integer> returnMaxResultsIfFirstKSubjectOrNull(Optional<String> subject) {             return subject.map((it) -> {                 Matcher grp = LIMITED_QUERY_TEMPLATE.matcher(it);                 return !grp.find() ? null : StringUtils.hasText(grp.group(4)) ? Integer.valueOf(grp.group(4)) : 1;             });         }         ...          private boolean matches(Optional<String> subject, Pattern pattern) {             return (Boolean)subject.map((it) -> {                 return pattern.matcher(it).find();             }).orElse(false);         }     } }
package org.springframework.data.repository.query.parser; public class Part {     private static final Pattern IGNORE_CASE = Pattern.compile("Ignor(ing|e)Case");     private final PropertyPath propertyPath;     private final Part.Type type;     private Part.IgnoreCaseType ignoreCase;     ...     public static enum Type {         BETWEEN(2, new String[]{"IsBetween", "Between"}),         IS_NOT_NULL(0, new String[]{"IsNotNull", "NotNull"}),         IS_NULL(0, new String[]{"IsNull", "Null"}),         LESS_THAN(new String[]{"IsLessThan", "LessThan"}),         LESS_THAN_EQUAL(new String[]{"IsLessThanEqual", "LessThanEqual"}),         GREATER_THAN(new String[]{"IsGreaterThan", "GreaterThan"}),         GREATER_THAN_EQUAL(new String[]{"IsGreaterThanEqual", "GreaterThanEqual"}),         BEFORE(new String[]{"IsBefore", "Before"}),         AFTER(new String[]{"IsAfter", "After"}),         NOT_LIKE(new String[]{"IsNotLike", "NotLike"}),         LIKE(new String[]{"IsLike", "Like"}),         STARTING_WITH(new String[]{"IsStartingWith", "StartingWith", "StartsWith"}),         ENDING_WITH(new String[]{"IsEndingWith", "EndingWith", "EndsWith"}),         IS_NOT_EMPTY(0, new String[]{"IsNotEmpty", "NotEmpty"}),         IS_EMPTY(0, new String[]{"IsEmpty", "Empty"}),         NOT_CONTAINING(new String[]{"IsNotContaining", "NotContaining", "NotContains"}),         CONTAINING(new String[]{"IsContaining", "Containing", "Contains"}),         NOT_IN(new String[]{"IsNotIn", "NotIn"}),         IN(new String[]{"IsIn", "In"}),         NEAR(new String[]{"IsNear", "Near"}),         WITHIN(new String[]{"IsWithin", "Within"}),         REGEX(new String[]{"MatchesRegex", "Matches", "Regex"}),         EXISTS(0, new String[]{"Exists"}),         TRUE(0, new String[]{"IsTrue", "True"}),         FALSE(0, new String[]{"IsFalse", "False"}),         NEGATING_SIMPLE_PROPERTY(new String[]{"IsNot", "Not"}),         SIMPLE_PROPERTY(new String[]{"Is", "Equals"});          private static final List<Part.Type> ALL = Arrays.asList(IS_NOT_NULL, IS_NULL, BETWEEN, LESS_THAN, LESS_THAN_EQUAL, GREATER_THAN, GREATER_THAN_EQUAL, BEFORE, AFTER, NOT_LIKE, LIKE, STARTING_WITH, ENDING_WITH, IS_NOT_EMPTY, IS_EMPTY, NOT_CONTAINING, CONTAINING, NOT_IN, IN, NEAR, WITHIN, REGEX, EXISTS, TRUE, FALSE, NEGATING_SIMPLE_PROPERTY, SIMPLE_PROPERTY);         public static final Collection<String> ALL_KEYWORDS;         private final List<String> keywords;         private final int numberOfArguments;         ...         static {             List<String> allKeywords = new ArrayList();             Iterator var1 = ALL.iterator();              while(var1.hasNext()) {                 Part.Type type = (Part.Type)var1.next();                 allKeywords.addAll(type.keywords);             }              ALL_KEYWORDS = Collections.unmodifiableList(allKeywords);         }     } }

可以看到单表操作的大部分需求jpa都为我们提供了现成的实现，但也支持我们使用@Query注解自定义查询sql，方便有sql基础的同学使用，sql可控性强。

package com.yizhu.repository;  import com.yizhu .entity.User; import org.springframework.data.jpa.repository.EntityGraph; import org.springframework.data.jpa.repository.JpaRepository; import org.springframework.data.jpa.repository.JpaSpecificationExecutor; import org.springframework.data.jpa.repository.Query; import org.springframework.data.repository.query.Param;  import java.util.List;  public interface UserRepository extends JpaRepository<User, Long>{      /**      * 查询所有用户信息      * @return      */     @Query(value = "from User u")     List<User> findAll();      /**      * 根据年龄查询用户信息      * @param age      * @return      */     @Query(value = "select * from t_user u where u.user_age = ?1", nativeQuery = true)     List<User> findAllByAge(Integer age);      /**      * 根据用户性别和所属组织名称查询用户信息      * @param userSex      * @param orgName      * @return      */     @Query(value = "select u from User u left join u.org o where u.userSex = :userSex and o.orgName = :orgName")     List<User> findUsersBySexAndOrg(@Param("userSex") Integer userSex, @Param("orgName") String orgName);  }

多表关联

@OneToOne、@OneToMany、@ManyToOne、@ManyToMany

@Entity @Table(name = "t_user") @NamedEntityGraph(name = "User.findUsers", attributeNodes = {@NamedAttributeNode("jobs"), @NamedAttributeNode("roles")}) @Data @Builder @NoArgsConstructor @AllArgsConstructor public class User implements Serializable {      private static final long serialVersionUID = 1L;      @ApiModelProperty(hidden = true)     @Id     @GeneratedValue(strategy = GenerationType.IDENTITY)     private Long id;      @ApiModelProperty(value = "用户名")     @Column(name = "user_name")     private String name;      @ApiModelProperty(value = "用户密码")     @Column(name = "user_password")     private String password;      @ApiModelProperty(value = "用户年龄")     @Column(name = "user_age")     private Integer age;      @ApiModelProperty(value = "用户性别")     @Column(name = "user_sex")     private Integer sex;      @ApiModelProperty(value = "所属组织id")     @Column(name = "org_id")     private Long orgId;      @ApiModelProperty(value = "用户信息")     @OneToOne     @JoinColumn(name = "id", updatable = false, insertable = false)     private UserInfo userInfo;      @ApiModelProperty(value = "用户所属组织")     @ManyToOne     @JoinColumn(name = "org_id", updatable = false, insertable = false)     private Organization org;      @ApiModelProperty(value = "用户角色")     @OneToMany     @JoinColumn(name = "user_id", referencedColumnName = "id", insertable = false, updatable = false)     @NotFound(action = NotFoundAction.IGNORE)     private Set<Role> roles;      @ApiModelProperty(value = "用户工作")     @ManyToMany     @JoinTable(             name = "t_user_job",             joinColumns = @JoinColumn(name = "user_id", referencedColumnName = "id"),             inverseJoinColumns = @JoinColumn(name = "job_id", referencedColumnName = "id")     )     @NotFound(action = NotFoundAction.IGNORE)     private Set<Job> jobs;

private Set<Role> roles;和private Set<Job> jobs;不能用同时使用List集合代替，会报错org.hibernate.loader.MultipleBagFetchException: cannot simultaneously fetch multiple bags: [com.yizhu.entity.User.jobs, com.yizhu.entity.User.roles]

动态查询

package com.yizhu.repository;  import com.yizhu.dto.UserQueryDto; import com.yizhu.entity.Organization; import com.yizhu.entity.User; import org.springframework.data.jpa.domain.Specification;  import javax.persistence.criteria.Join; import javax.persistence.criteria.JoinType; import javax.persistence.criteria.Predicate; import java.util.ArrayList; import java.util.List; import java.util.Optional;  public class UserSpecs {      public static Specification<User> listQuerySpec(UserQueryDto userQueryDto){         return (root, query, builder) -> {             List<Predicate> predicates = new ArrayList<>();              Optional.ofNullable(userQueryDto.getId()).ifPresent(i -> predicates.add(builder.equal(root.get("id"), i)));             Optional.ofNullable(userQueryDto.getName()).ifPresent(n -> predicates.add(builder.equal(root.get("name"), n)));             Optional.ofNullable(userQueryDto.getAge()).ifPresent(a -> predicates.add(builder.equal(root.get("age"), a)));             Optional.ofNullable(userQueryDto.getOrgId()).ifPresent(oi -> predicates.add(builder.equal(root.get("orgId"), oi)));             Optional.ofNullable(userQueryDto.getOrgName()).ifPresent(on -> {                 Join<User, Organization> userJoin = root.join(root.getModel().getSingularAttribute("org", Organization.class), JoinType.LEFT);                 predicates.add(builder.equal(userJoin.get("orgName"), on));             });              return builder.and(predicates.toArray(new Predicate[predicates.size()]));         };     } }
package com.yizhu.service;  import com.yizhu.dto.UserQueryDto; import com.yizhu.entity.User; import com.yizhu.repository.UserRepository; import com.yizhu.repository.UserSpecs; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service;  import java.util.List;  @Service public class UserService {      @Autowired     private UserRepository userRepository;      public List<User> findUsersDynamic(UserQueryDto userQueryDto){         return userRepository.findAll(UserSpecs.listQuerySpec(userQueryDto));     } }

审计功能使用

在启动类添加@EnableJpaAuditing注解表示开启jpa审计功能

package com.yizhu;  import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.data.jpa.repository.config.EnableJpaAuditing;  @EnableJpaAuditing @SpringBootApplication public class DemoApplication {      public static void main(String[] args) {         SpringApplication.run(DemoApplication.class, args);     } }

在需要使用审计功能的实体类添加@EntityListeners(AuditingEntityListener.class)注解

package com.yizhu.entity;  import lombok.Builder; import lombok.Data; import org.springframework.data.jpa.domain.support.AuditingEntityListener;  import javax.persistence.*; import java.io.Serializable; import java.util.Date;  @Entity @Table(name = "t_role") @Data @Builder @EntityListeners(AuditingEntityListener.class) public class Role implements Serializable {     private static final long serialVersionUID=1L;      @ApiModelProperty(hidden = true)     @Id     @GeneratedValue(strategy = GenerationType.AUTO)     private Long id;      private String roleName;      @CreatedDate     private Date createTime;          @CreatedBy     private Long createId;          @LastModifiedDate     private Date updateTime;          @LastModifiedBy     private Long updateId; }

实现AuditorAware接口，告诉容器当前登录人id

package com.yizhu.configuration;  import org.springframework.data.domain.AuditorAware; import org.springframework.web.context.request.RequestContextHolder; import org.springframework.web.context.request.ServletRequestAttributes;  import java.util.Optional;  public class UserAuditorAwareImpl implements AuditorAware<Long> {     @Override     public Optional<Long> getCurrentAuditor() {         // 从session中获取登录人id         ServletRequestAttributes servletRequestAttributes = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();         Long userId = (Long)servletRequestAttributes.getRequest().getSession().getAttribute("userId");         return Optional.of(userId);     } }

ok，然后jpa就会根据ID和Version判断当前操作是更新还是新增数据，新增时会注入当前登录人id到标有@CreateBy注解的字段上，当前时间注入到标有@CreateTime注解字段上；更新时则注入到@LastModifiedBy和@LastModifiedDate对应的字段上。想详细了解的可查看org.springframework.data.jpa.domain.support.AuditingEntityListener源码。

常见的坑

  • N+1问题，当使用@ManyToMany、@ManyToOne、@OneToMany、@OneToOne关联
    关系的时候，FetchType怎么配置LAZY或者EAGER。SQL真正执行的时
    候是由一条主表查询和N条子表查询组成的。这种查询效率一般比较
    低下，比如子对象有N个就会执行N+1条SQL。使用JPA 2.1推出来的@EntityGraph、@NamedEntityGraph可以解决该问题。如下。
@ApiModel @Entity @Table(name = "t_user") @NamedEntityGraph(name = "User.findUsers", attributeNodes = {@NamedAttributeNode("jobs"), @NamedAttributeNode("roles")}) @Data @Builder @NoArgsConstructor @AllArgsConstructor public class User implements Serializable {      private static final long serialVersionUID = 1L;      @ApiModelProperty(hidden = true)     @Id     @GeneratedValue(strategy = GenerationType.IDENTITY)     private Long id;          // 省略其他属性 }
package com.yizhu.repository;  import com.yizhu.entity.User; import org.springframework.data.jpa.repository.EntityGraph; import org.springframework.data.jpa.repository.JpaRepository; import org.springframework.data.jpa.repository.JpaSpecificationExecutor; import org.springframework.data.jpa.repository.Query; import org.springframework.data.repository.query.Param; import java.util.List;  public interface UserRepository extends JpaRepository<User, Long>, JpaSpecificationExecutor<User> {      /**      * 根据id查询用户信息      * @param id      * @return      */     @EntityGraph(value = "User.findUsers", type = EntityGraph.EntityGraphType.FETCH)     User findAllById(Long id);      /**      * 根据name查询用户信息      * @param name      * @return      */     @EntityGraph(value = "User.findUsers", type = EntityGraph.EntityGraphType.FETCH)     @Query(value = "select * from t_user where user_name = :name", nativeQuery = true)     List<User> findAllByUserName(@Param("name") String name); }
  • 所有的注解要么全配置在字段上，要么全配置在get方法上，不能混用，混用就会启动不起来，但是语法配置没有问题。
  • 所有的关联都是支持单向关联和双向关联的，视具体业务场景而定。JSON序列化的时候使用双向注解会产生死循环，需要人为手动转化一次，或者使用@JsonIgnore。
  • 在所有的关联查询中，表一般是不需要建立外键索引的。@mappedBy的使用需要注意。
  • 级联删除比较危险，建议考虑清楚，或者完全掌握。
  • 不同的关联关系的配置，@JoinClumn里面的name、referencedColumnName代表的意思是不一样的，很容易弄混，可以根据打印出来的SQL做调整。
  • 当配置这些关联关系的时候建议大家直接在表上面，把外键建好，然后通过后面我们介绍的开发工具直接生成，这样可以减少自己调试的时间。

JPA常用注解

摘自《Spring Data JPA从入门到精通》

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