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使用 Spring Data JPA 和 Querydsl 构建 REST 查询语言

1、概览 {#1概览}

在前两篇文章中,我们使用 JPA Criteria 和 Spring Data JPA Specification 构建了相同的搜索/过滤功能。

本文将带你了解如何使用 Spring Data JPA 和 Querydsl 构建 REST API 查询语言。

2、Querydsl 配置 {#2querydsl-配置}

首先,在 pom.xml 中添加以下依赖:

<dependency> 
    <groupId>com.querydsl</groupId> 
    <artifactId>querydsl-apt</artifactId> 
    <version>4.2.2</version>
    </dependency>
<dependency> 
    <groupId>com.querydsl</groupId> 
    <artifactId>querydsl-jpa</artifactId> 
    <version>4.2.2</version> 
</dependency>

还需要配置 APT(注解处理工具)插件:

<plugin>
    <groupId>com.mysema.maven</groupId>
    <artifactId>apt-maven-plugin</artifactId>
    <version>1.1.3</version>
    <executions>
        <execution>
            <goals>
                <goal>process</goal>
            </goals>
            <configuration>
                <outputDirectory>target/generated-sources/java</outputDirectory>
                <processor>com.mysema.query.apt.jpa.JPAAnnotationProcessor</processor>
            </configuration>
        </execution>
    </executions>
</plugin>

该插件会根据实体类生成 Q 开头的查询类。

关于如何在 Spring Boot 中使用 QueryDSL,你可以参阅 这篇文章

3、MyUser 实体 {#3myuser-实体}

定义 MyUser 实体,用于在 API 中进行搜索:

@Entity
public class MyUser {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    private String firstName;
    private String lastName;
    private String email;

    private int age;
}

4、使用 PathBuilder 自定义 Predicate {#4使用-pathbuilder-自定义-predicate}

根据一些任意约束条件创建一个自定义 Predicate

这里使用 PathBuilder 而不是自动生成的查询类,因为我们需要为更抽象的用法动态创建 Path

public class MyUserPredicate {

    private SearchCriteria criteria;

    public BooleanExpression getPredicate() {
        PathBuilder<MyUser> entityPath = new PathBuilder<>(MyUser.class, "user");

        if (isNumeric(criteria.getValue().toString())) {
            NumberPath<Integer> path = entityPath.getNumber(criteria.getKey(), Integer.class);
            int value = Integer.parseInt(criteria.getValue().toString());
            switch (criteria.getOperation()) {
                case ":":
                    return path.eq(value);
                case ">":
                    return path.goe(value);
                case "<":
                    return path.loe(value);
            }
        } 
        else {
            StringPath path = entityPath.getString(criteria.getKey());
            if (criteria.getOperation().equalsIgnoreCase(":")) {
                return path.containsIgnoreCase(criteria.getValue().toString());
            }
        }
        return null;
    }
}

注意 Predicate 的实现是如何通用地处理多种类型的操作的。这是因为查询语言顾名思义是一种开放式语言,你可以使用任何支持的操作,对任何字段进行过滤。

为了表示这种开放式过滤标准,我们使用了一种简单但相当灵活的实现方式 - SearchCriteria

public class SearchCriteria {
    private String key;
    private String operation;
    private Object value;
}

SearchCriteria 包含表示约束条件的详细信息:

  • key:字段名 - 例如:firstNameage
  • operation:操作,例如:等于、小于 ... 等
  • value:字段值,例如:john25

5、MyUserRepository {#5myuserrepository}

定义 MyUserRepository,继承 QuerydslPredicateExecutor,以使用 Predicate 过滤搜索结果:

public interface MyUserRepository extends JpaRepository<MyUser, Long>, 
  QuerydslPredicateExecutor<MyUser>, QuerydslBinderCustomizer<QMyUser> {
    @Override
    default public void customize(
      QuerydslBindings bindings, QMyUser root) {
        bindings.bind(String.class)
          .first((SingleValueBinding<StringPath, String>) StringExpression::containsIgnoreCase);
        bindings.excluding(root.email);
      }
}

注意,在这里使用的是 MyUser 实体对应查询类: QMyUser

6、组合 Predicate {#6组合-predicate}

接下来,看看如何组合 Predicate,以使用多个约束条件来过滤结果。

使用 MyUserPredicatesBuilder 来组合 Predicate

public class MyUserPredicatesBuilder {
    private List<SearchCriteria> params;

    public MyUserPredicatesBuilder() {
        params = new ArrayList<>();
    }

    public MyUserPredicatesBuilder with(
      String key, String operation, Object value) {
  
        params.add(new SearchCriteria(key, operation, value));
        return this;
    }

    public BooleanExpression build() {
        if (params.size() == 0) {
            return null;
        }

        List predicates = params.stream().map(param -> {
            MyUserPredicate predicate = new MyUserPredicate(param);
            return predicate.getPredicate();
        }).filter(Objects::nonNull).collect(Collectors.toList());
        
        BooleanExpression result = Expressions.asBoolean(true).isTrue();
        for (BooleanExpression predicate : predicates) {
            result = result.and(predicate);
        }        
        return result;
    }
}

7、测试搜索过滤 {#7测试搜索过滤}

先初始化几个测试数据,用于测试:

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = { PersistenceConfig.class })
@Transactional
@Rollback
public class JPAQuerydslIntegrationTest {

    @Autowired
    private MyUserRepository repo;

    private MyUser userJohn;
    private MyUser userTom;

    @Before
    public void init() {
        userJohn = new MyUser();
        userJohn.setFirstName("John");
        userJohn.setLastName("Doe");
        userJohn.setEmail("john@doe.com");
        userJohn.setAge(22);
        repo.save(userJohn);

        userTom = new MyUser();
        userTom.setFirstName("Tom");
        userTom.setLastName("Doe");
        userTom.setEmail("tom@doe.com");
        userTom.setAge(26);
        repo.save(userTom);
    }
}

根据 lastName 检索用户:

@Test
public void givenLast_whenGettingListOfUsers_thenCorrect() {
    MyUserPredicatesBuilder builder = new MyUserPredicatesBuilder().with("lastName", ":", "Doe");

    Iterable<MyUser> results = repo.findAll(builder.build());
    assertThat(results, containsInAnyOrder(userJohn, userTom));
}

根据 firstNamelastName 检索用户:

@Test
public void givenFirstAndLastName_whenGettingListOfUsers_thenCorrect() {
    MyUserPredicatesBuilder builder = new MyUserPredicatesBuilder()
      .with("firstName", ":", "John").with("lastName", ":", "Doe");

    Iterable<MyUser> results = repo.findAll(builder.build());

    assertThat(results, contains(userJohn));
    assertThat(results, not(contains(userTom)));
}

检索 lastName 等于 Doeage 大于 25 的用户。

@Test
public void givenLastAndAge_whenGettingListOfUsers_thenCorrect() {
    MyUserPredicatesBuilder builder = new MyUserPredicatesBuilder()
      .with("lastName", ":", "Doe").with("age", ">", "25");

    Iterable<MyUser> results = repo.findAll(builder.build());

    assertThat(results, contains(userTom));
    assertThat(results, not(contains(userJohn)));
}

检索不存在的记录:

@Test
public void givenWrongFirstAndLast_whenGettingListOfUsers_thenCorrect() {
    MyUserPredicatesBuilder builder = new MyUserPredicatesBuilder()
      .with("firstName", ":", "Adam").with("lastName", ":", "Fox");

    Iterable<MyUser> results = repo.findAll(builder.build());
    assertThat(results, emptyIterable());
}

根据 firstName 进行模糊检索:

@Test
public void givenPartialFirst_whenGettingListOfUsers_thenCorrect() {
    MyUserPredicatesBuilder builder = new MyUserPredicatesBuilder().with("firstName", ":", "jo");

    Iterable<MyUser> results = repo.findAll(builder.build());

    assertThat(results, contains(userJohn));
    assertThat(results, not(contains(userTom)));
}

8、UserController {#8usercontroller}

最后,构建 REST API,整合所有内容。

定义 UserController,它有一个 findAll() 方法,该方法接收一个 search 查询参数:

@Controller
public class UserController {

    @Autowired
    private MyUserRepository myUserRepository;

    @RequestMapping(method = RequestMethod.GET, value = "/myusers")
    @ResponseBody
    public Iterable<MyUser> search(@RequestParam(value = "search") String search) {
        MyUserPredicatesBuilder builder = new MyUserPredicatesBuilder();

        if (search != null) {
            Pattern pattern = Pattern.compile("(\w+?)(:|<|>)(\w+?),");
            Matcher matcher = pattern.matcher(search + ",");
            while (matcher.find()) {
                builder.with(matcher.group(1), matcher.group(2), matcher.group(3));
            }
        }
        BooleanExpression exp = builder.build();
        return myUserRepository.findAll(exp);
    }
}

测试 URL:

http://localhost:8080/myusers?search=lastName:doe,age>25

响应如下:

[{
    "id":2,
    "firstName":"tom",
    "lastName":"doe",
    "email":"tom@doe.com",
    "age":26
}]

9、总结 {#9总结}

本文介绍了如何使用 Spring Data JPA 和 Querydsl 构建 REST 查询语言,以及如何在 REST API 中应用。


Ref:https://www.baeldung.com/rest-api-search-language-spring-data-querydsl

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