左连接不使用 Hibernate 连接关系

Question

Suppose I have one hibernate jpa entity-A:

public class A{
   id ,//pk
   name,
   age
   //getters and setters
}

Another Enitity-B:

public class B{
   id, //pk
   a_id, //pk id of A
   degree,
   institute
   //getters and setters
}

Here to note that entity A and B don't have implicit relation among them, a_id in B table is handled manually and hence- the relation is like one to many(A-->B) but not the jpa-hibernate relation. And, My FullDto has all the A's properties and List of B:

public class FullDto{
      id ,//pk
      name,
      age,
     List<B> bList;

    public class FullDto(id, age, name, bList)
     {
        this.id.id;
        this.age=age;
        this.name=name;
        this.bList=bList;
     }
    //getters and setters

}

Now, I want to pull everything(both A and B tables in one go) from repository interface of A like this:

public interface ARepository extends JpaRepository<A, Long> {
@Query("select " +
            "new packageName.FullDto(a.id, a.name, a.age, b) " +
            "from" +
            "   A a " +
            " left join B  b "+
            " on a.id=b.a_id "+
            "where " +
            "   a.id=:id ")
      FullDto getFullDetails(@Param("id") Long id);
}

But this seems not the way to do this!

When I tried this way: I got this error

WARN ] 2021-08-12 13:20:13.091 [restartedMain] TemplateRenderer - HHH000174: Function template anticipated 4 arguments, but 1 arguments encountered [ERROR] 2021-08-12 13:20:13.123 [restartedMain] ErrorTracker - line 1:51: unexpected token: ) [ERROR] 2021-08-12 13:20:13.123 [restartedMain] ErrorTracker - line 1:51: unexpected token: ) antlr.NoViableAltException: unexpected token: ) at org.hibernate.hql.internal.antlr.HqlBaseParser.negatedExpression(HqlBaseParser.java:2534) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final] at org.hibernate.hql.internal.antlr.HqlBaseParser.logicalAndExpression(HqlBaseParser.java:2438) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final] at org.hibernate.hql.internal.antlr.HqlBaseParser.logicalOrExpression(HqlBaseParser.java:2403) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final] at org.hibernate.hql.internal.antlr.HqlBaseParser.expression(HqlBaseParser.java:2116) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final] at org.hibernate.hql.internal.antlr.HqlBaseParser.aliasedExpression(HqlBaseParser.java:2357) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final] at org.hibernate.hql.internal.antlr.HqlBaseParser.selectedPropertiesList(HqlBaseParser.java:1390) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final] at org.hibernate.hql.internal.antlr.HqlBaseParser.newExpression(HqlBaseParser.java:1434) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final] at org.hibernate.hql.internal.antlr.HqlBaseParser.selectClause(HqlBaseParser.java:1306) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final] at org.hibernate.hql.internal.antlr.HqlBaseParser.selectFrom(HqlBaseParser.java:1040) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final] at org.hibernate.hql.internal.antlr.HqlBaseParser.queryRule(HqlBaseParser.java:748) ~[hibernate-core-5.3.7.Final.8 8202878901088:5.3.7.Final] at org.hibernate.hql.internal.antlr.HqlBaseParser.selectStatement(HqlBaseParser.java:319) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final] at org.hibernate.hql.internal.antlr.HqlBaseParser.statement(HqlBaseParser.java:198) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final] at org.hibernate.hql.internal.ast.QueryTranslatorImpl.parse(QueryTranslatorImpl.java:289) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final] at org.hibernate.hql.internal.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:188) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final] at org.hibernate.hql.internal.ast.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:143) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final] at org.hibernate.engine.query.spi.HQLQueryPlan.(HQLQueryPlan.java:119) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final] at org.8839837993068 8.engine.query.spi.HQLQueryPlan.(HQLQueryPlan.java:80) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final] at org.hibernate.engine.query.spi.QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:153) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final] at org.hibernate.internal.AbstractSharedSessionContract.getQueryPlan(AbstractSharedSessionContract.java:595) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final] at org.hibernate.internal.AbstractSharedSessionContract.createQuery(AbstractSharedSessionContract.java:704) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final] at org.hibernate.internal.AbstractSessionImpl.createQuery(AbstractSessionImpl.java:23) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final] at sun.reflect.GeneratedMethodAccessor88.invoke(Unknown Source) ~[?:?] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_121] at 88213246 945888.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_121] at org.springframework.orm.jpa.ExtendedEntityManagerCreator$ExtendedEntityManagerInvocationHandler.invoke(ExtendedEntityManagerCreator.java:350) ~[spring-orm-5.1.4.RELEASE.jar:5.1.4.RELEASE] at com.sun.proxy.$Proxy155.createQuery(Unknown Source) ~[?:?] at org.springframework.data.jpa.repository.query.SimpleJpaQuery.validateQuery(SimpleJpaQuery.java:87) ~[spring-data-jpa-2.1.4.RELEASE.jar:2.1.4.RELEASE] at org.springframework.data.jpa.repository.query.SimpleJpaQuery.(SimpleJpaQuery.java:63) ~[spring-data-jpa-2.1.4.RELEASE.jar:2.1.4.RELEASE] at org.springframework.data.jpa.repository.query.JpaQueryFactory.fromMethodWithQueryString(JpaQueryFactory.java:76) ~[spring-data-jpa-2.1.4.RELEASE.jar:2.1.4.RELEASE] at org.springframework.data.jpa.repository.query.J paQueryFactory.fromQueryAnnotation(JpaQueryFactory.java:56) ~[spring-data-jpa-2.1.4.RELEASE.jar:2.1.4.RELEASE] at org.springframework.data.jpa.repository.query.JpaQueryLookupStrategy$DeclaredQueryLookupStrategy.resolveQuery(JpaQueryLookupStrategy.java:139) ~[spring-data-jpa-2.1.4.RELEASE.jar:2.1.4.RELEASE] at org.springframework.data.jpa.repository.query.JpaQueryLookupStrategy$CreateIfNotFoundQueryLookupStrategy.resolveQuery(JpaQueryLookupStrategy.java:206) ~[spring-data-jpa-2.1.4.RELEASE.jar:2.1.4.RELEASE] at org.springframework.data.jpa.repository.query.JpaQueryLookupStrategy$AbstractQueryLookupStrategy.resolveQuery(JpaQueryLookupStrategy.java:79) ~[spring-data-jpa-2.1.4.RELEASE.jar:2.1.4.RELEASE] at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.lookupQuery(RepositoryFactorySupport.java:566) ~[spring- data-commons-2.1.4.RELEASE.jar:2.1.4.RELEASE] at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.lambda$mapMethodsToQuery$1(RepositoryFactorySupport.java:559) ~[spring-data-commons-2.1.4.RELEASE.jar:2.1.4.RELEASE] at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193) ~[?:1.8.0_121]...

How to get all the data without using hibernate oneToMany and ManyToOne relational join?

Answer 1

This is not possible as the constructor syntax only allows to pass singular attributes ie there is no such thing as aggregation of records on this level, so you would have to create some kind of IntermediateDto and aggregate this into a FullDto through some custom code like explain by Vlad Mihalcea here: https://vladmihalcea.com/one-to-many-dto-projection-hibernate/

I think this is a perfect use case forBlaze-Persistence Entity Views though as it employs a more efficient approach that is easier to use and maintain.

I created the library to allow easy mapping between JPA models and custom interface or abstract class defined models, something like Spring Data Projections on steroids. The idea is that you define your target structure(domain model) the way you like and map attributes(getters) via JPQL expressions to the entity model.

A DTO model for your use case could look like the following with Blaze-Persistence Entity-Views:

@EntityView(A.class)
public interface FullDto {
    @IdMapping
    Long getId();
    String getName();
    Long getAge();
    @Mapping("B[aId = VIEW(id)]")
    Set<BDto> getBList();

    @EntityView(B.class)
    interface BDto {
        @IdMapping
        Long getId();
        String getName();
    }
}

Querying is a matter of applying the entity view to a query, the simplest being just a query by id.

FullDto a = entityViewManager.find(entityManager, FullDto.class, id);

The Spring Data integration allows you to use it almost like Spring Data Projections: https://persistence.blazebit.com/documentation/entity-view/manual/en_US/index.html#spring-data-features

Page<FullDto> findAll(Pageable pageable);

The best part is, it will only fetch the state that is actually necessary!

Answer 2

FullDto must have a constructor that matches the projection in your query. And you must provide the fully qualified name of FullDto in the query:

 @Query("select " +
        "   new packagename.FullDto(a.id, a.name, a.age)" +
        " from A a " +
        " left join B b on a.id = b.a_id "+
        " where a.id=:id ")
  FullDto getFullDetails(@Param("id") Long id);

Answer 3

The DTO projection needs to use an constructor expression to fill-up the DTO.

Further the DTO class name shall be fully qualified.