[QueryDsl] QueryDslSupport 클래스 대안

package com.example.springboot3.test.example.qdsl;

import com.mysema.commons.lang.Assert;
import com.querydsl.core.types.EntityPath;
import com.querydsl.core.types.Expression;
import com.querydsl.core.types.dsl.PathBuilder;
import com.querydsl.jpa.impl.JPAQuery;
import com.querydsl.jpa.impl.JPAQueryFactory;
import jakarta.annotation.PostConstruct;
import jakarta.persistence.EntityManager;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.jpa.repository.support.JpaEntityInformation;
import org.springframework.data.jpa.repository.support.JpaEntityInformationSupport;
import org.springframework.data.jpa.repository.support.Querydsl;
import org.springframework.data.querydsl.SimpleEntityPathResolver;
import org.springframework.data.support.PageableExecutionUtils;
import org.springframework.stereotype.Repository;

import java.util.List;
import java.util.function.Function;

@Repository
public abstract class Querydsl4RepositorySupport {

    private final Class domainClass;
    private Querydsl querydsl;
    private EntityManager entityManager;
    private JPAQueryFactory queryFactory;

    public Querydsl4RepositorySupport(Class<?> domainClass) {
        Assert.notNull(domainClass, "Domain class must not be null!");
        this.domainClass = domainClass;
    }

    @Autowired
    public void setEntityManager(EntityManager entityManager) {
        Assert.notNull(entityManager, "EntityManager must not be null!");
        JpaEntityInformation entityInformation =
                JpaEntityInformationSupport.getEntityInformation(domainClass, entityManager);
        SimpleEntityPathResolver resolver = SimpleEntityPathResolver.INSTANCE;
        EntityPath path = resolver.createPath(entityInformation.getJavaType());
        this.entityManager = entityManager;
        this.querydsl = new Querydsl(entityManager, new
            PathBuilder<>(path.getType(), path.getMetadata()));
        this.queryFactory = new JPAQueryFactory(entityManager);
    }

    @PostConstruct
    public void validate() {
        Assert.notNull(entityManager, "EntityManager must not be null!");
        Assert.notNull(querydsl, "Querydsl must not be null!");
        Assert.notNull(queryFactory, "QueryFactory must not be null!");
    }

    protected JPAQueryFactory getQueryFactory() {
        return queryFactory;
    }
    protected Querydsl getQuerydsl() {
        return querydsl;
    }
    protected EntityManager getEntityManager() {
        return entityManager;
    }
    protected <T> JPAQuery<T> select(Expression<T> expr) {
        return getQueryFactory().select(expr);
    }

    protected <T> JPAQuery<T> selectFrom(EntityPath<T> from) {
        return getQueryFactory().selectFrom(from);
    }
    protected <T> Page<T> applyPagination(
        Pageable pageable,
        Function<JPAQueryFactory, JPAQuery> contentQuery) {
        JPAQuery jpaQuery = contentQuery.apply(getQueryFactory());
        List<T> content = getQuerydsl().applyPagination(pageable,
                                                        jpaQuery).fetch();
        return PageableExecutionUtils.getPage(content, pageable,
                                              jpaQuery::fetchCount);
    }
    protected <T> Page<T> applyPagination(Pageable pageable,
                                          Function<JPAQueryFactory, JPAQuery> contentQuery, Function<JPAQueryFactory, JPAQuery> countQuery) {
        JPAQuery jpaContentQuery = contentQuery.apply(getQueryFactory());
        List<T> content = getQuerydsl().applyPagination(pageable,
                jpaContentQuery).fetch();
        JPAQuery countResult = countQuery.apply(getQueryFactory());
        return PageableExecutionUtils.getPage(content, pageable,
                countResult::fetchCount);
    }
}

• 영한님이 만드신 클래스를 사용해서 수행한다면

• 좀더 편리하게 Querydsl 을 실무면에서 사용할 수 있다고 한다.

• 하지만..
  • fetchCount() , fetchResult 는 지금 deprecated 된 상태이다.

package com.example.springboot3.test.example.qdsl;

import com.mysema.commons.lang.Assert;
import com.querydsl.core.types.EntityPath;
import com.querydsl.core.types.Expression;
import com.querydsl.core.types.dsl.PathBuilder;
import com.querydsl.jpa.impl.JPAQuery;
import com.querydsl.jpa.impl.JPAQueryFactory;
import jakarta.annotation.PostConstruct;
import jakarta.persistence.EntityManager;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.jpa.repository.support.JpaEntityInformation;
import org.springframework.data.jpa.repository.support.JpaEntityInformationSupport;
import org.springframework.data.jpa.repository.support.Querydsl;
import org.springframework.data.querydsl.SimpleEntityPathResolver;
import org.springframework.stereotype.Repository;

import java.util.List;
import java.util.function.Function;

import static org.springframework.data.support.PageableExecutionUtils.*;

@Repository
public abstract class Querydsl4RepositorySupport {
    private final Class domainClass;
    private Querydsl querydsl;
    private EntityManager entityManager;
    private JPAQueryFactory queryFactory;
    
    // 1. 도메인 class 받기 (ex)Member.class)
    public Querydsl4RepositorySupport(Class<?> domainClass) {
        Assert.notNull(domainClass, "Domain class must not be null!");
        this.domainClass = domainClass;
    }
    
    // 2. EntityManager 주입받기
    @Autowired
    public void setEntityManager(EntityManager entityManager) {
        Assert.notNull(entityManager, "EntityManager must not be null!");
        // 2-1. Path를 잡아야 Sort 명령시에 오류가 안난다.
        JpaEntityInformation entityInformation =
            JpaEntityInformationSupport.getEntityInformation(domainClass, entityManager);
        SimpleEntityPathResolver resolver = SimpleEntityPathResolver.INSTANCE;
        EntityPath path = resolver.createPath(entityInformation.getJavaType());
        // 2-2. entityManager 주입 받은 것으로 querydsl, queryFactory 생성
        this.entityManager = entityManager;
        this.querydsl = new Querydsl(entityManager, new
            PathBuilder<>(path.getType(), path.getMetadata()));
        this.queryFactory = new JPAQueryFactory(entityManager);
    }
    
    protected JPAQueryFactory getQueryFactory() {
        return queryFactory;
    }
    protected Querydsl getQuerydsl() {
        return querydsl;
    }
    protected EntityManager getEntityManager() {
        return entityManager;
    }
    
    @PostConstruct
    public void validate() {
        Assert.notNull(entityManager, "EntityManager must not be null!");
        Assert.notNull(querydsl, "Querydsl must not be null!");
        Assert.notNull(queryFactory, "QueryFactory must not be null!");
    }
    protected <T> JPAQuery<T> select(Expression<T> expr) {
        return getQueryFactory().select(expr);
    }
    protected <T> JPAQuery<T> selectFrom(EntityPath<T> from) {
        return getQueryFactory().selectFrom(from);
    }
    protected <T> Page<T> applyPagination(
        Pageable pageable,
        Function<JPAQueryFactory, JPAQuery> contentQuery, Function<JPAQueryFactory,
        JPAQuery> countQuery
    ) {
        JPAQuery jpaContentQuery = contentQuery.apply(getQueryFactory());
        List<T> content = getQuerydsl().applyPagination(
                                           pageable,
                                           jpaContentQuery
                                       )
                                       .fetch();
        JPAQuery<Long> countResult = countQuery.apply(getQueryFactory());
        
        return getPage(content, pageable,
                                                                               countResult::fetchOne
        );
    }
}

• 위 클래스를 사용하라고한다.

• fetchOne 은 countQuery 의 결과가 항상 단일값임을 보장하기 위해 설정되었으며,

• 이전 fetchCount 의 경우

JPAQuery countResult = countQuery.apply(getQueryFactory());

에서 countResult의 갯수를 들고올수있었지만..

그렇게 사용하지 못해서

JPAQuery<Long> countResult = countQuery.apply(getQueryFactory());

• 제너릭으로 Long 을 설정후

• countResult::fetchOne 을 설정하여 카운트의 값을 들고오는 것 같다.

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