SpringData JPA多对一查询

实体类：

①PaperStore类

package com.sssp.entity;import Java.util.Date;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.ManyToOne;import javax.persistence.Table;@Table(name="PaperStore")@Entitypublic class PaperStore {    private Integer id;    private String paperName;    private Vocation vocation;    private String paperType;    private String paperDegree;    private Integer paperPublish;    private Integer assembleMode;    private Date paperDate;    private String examTime;    @GeneratedValue    @Id    public Integer getId() {        return id;    }    public void setId(Integer id) {        this.id = id;    }    public String getPaperName() {        return paperName;    }    public void setPaperName(String paperName) {        this.paperName = paperName;    }    @JoinColumn(name="Vocation_Id")    @ManyToOne    public Vocation getVocation() {        return vocation;    }    public void setVocation(Vocation vocation) {        this.vocation = vocation;    }    public String getPaperType() {        return paperType;    }    public void setPaperType(String paperType) {        this.paperType = paperType;    }    public String getPaperDegree() {        return paperDegree;    }    public void setPaperDegree(String paperDegree) {        this.paperDegree = paperDegree;    }    public Integer getPaperPublish() {        return paperPublish;    }    public void setPaperPublish(Integer paperPublish) {        this.paperPublish = paperPublish;    }    public Integer getAssembleMode() {        return assembleMode;    }    public void setAssembleMode(Integer assembleMode) {        this.assembleMode = assembleMode;    }    public Date getPaperDate() {        return paperDate;    }    public void setPaperDate(Date paperDate) {        this.paperDate = paperDate;    }    public String getExamTime() {        return examTime;    }    public void setExamTime(String examTime) {        this.examTime = examTime;    }    @Override    public String toString() {        return "PaperStore [id=" + id + ", paperName=" + paperName + ", vocation=" + vocation + ", paperType="                + paperType + ", paperDegree=" + paperDegree + ", paperPublish=" + paperPublish + ", assembleMode="                + assembleMode + ", paperDate=" + paperDate + ", examTime=" + examTime + "]";    }}

②QuestionPaper类

package com.sssp.entity;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.ManyToOne;import javax.persistence.Table;@Table(name="Question_Paper")@Entitypublic class QuestionPaper {    private Integer id;    private PaperStore paperStore;    private QuestionInfo questionInfo;    @GeneratedValue    @Id    public Integer getId() {        return id;    }    public void setId(Integer id) {        this.id = id;    }    @JoinColumn(name="Paper_Id")    @ManyToOne    public PaperStore getPaperStore() {        return paperStore;    }    public void setPaperStore(PaperStore paperStore) {        this.paperStore = paperStore;    }    @JoinColumn(name="Question_Id")    @ManyToOne    public QuestionInfo getQuestionInfo() {        return questionInfo;    }    public void setQuestionInfo(QuestionInfo questionInfo) {        this.questionInfo = questionInfo;    }}

③repository

import org.springframework.data.jpa.repository.JpaRepository;import org.springframework.data.jpa.repository.JpaSpecificationExecutor;import org.springframework.data.jpa.repository.Query;import com.sssp.entity.PaperStore;import com.sssp.entity.QuestionPaper;public interface QuestionPaperRepository extends JpaRepository<QuestionPaper, Integer>,JpaSpecificationExecutor<QuestionPaper>{        public List<QuestionPaper> getByPaperStore(PaperStore paperStore);        @Query("SELECT qp FROM QuestionPaper qp INNER JOIN qp.paperStore ps WHERE ps.id = ?1")    List<QuestionPaper> getQuestionPaper(Integer id);}

需求：通过paperId得到QuestionPaper，一个paperId对应多个QuestionPaper

方法一：先查询PaperStore，再通过PaperStore查询QuestionPaper

service层：

PaperStore paperStore = paperStoreRepository.getById(id);

List<QuestionPaper> questionPapers= questionPaperRepository.getByPaperStore(paperStore);

方法二：通过@Query注解

service层：

List<QuestionPaper> questionPapers= questionPaperRepository.getQuestionPaper(id);

方法三：Repository继承JpaSpecificationExecutor

service层：

Specification<QuestionPaper> specification = new Specification<QuestionPaper>() {            @Override            public Predicate toPredicate(Root<QuestionPaper> root, CriteriaQuery<?> query, CriteriaBuilder cb) {                Join<QuestionPaper, PaperStore> join = root.join("paperStore",JoinType.INNER);                Path<Integer> exp = join.get("id");                return cb.ge(exp, id);            }        };        List<QuestionPaper> questionPapers= questionPaperRepository.findAll(specification);

方法四：属性的连缀

@Query("SELECT qp.questionInfo.questionId FROM QuestionPaper qp WHERE qp.paperStore.id = ?1")
    List<Integer> getQuestionId(Integer id);