通过jpa查询多对一关系时的性能问题

Question

我使用spring-boot-data-jpa-2.0从db获取数据。一个表具有多对一关系，并且查询速度太慢，带有外键的1000行数据将花费15s，但是通过本机sql它将仅花费0.07s。我搜索了问题，发现这是因为1 + n问题。

某些表示在hql中使用'join fetch'的解决方案可以解决。当我在hql中使用“ join fetch”时，查询速度不会改变。

该系统设计为具有Spring Boot框架的纯休息服务。

合同实体

import java.time.LocalDateTime;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

@Entity
@Table(name = "MA_CONTRACTINFO_B")

public class MaContractinfoB implements java.io.Serializable {

    // Fields

    private String contractcd;
    private MaDepartmentB maDepartmentB;
    private Double contractid;
    private String contractnm;
    private String partya;
    private String deputycontract;
    private String prjtype;
    private Double fundt;
    private String bustype;
    private String contractstatus;
    private Double contractyear;
    private String fundratio;
    private LocalDateTime signdate;
    private String prj;
    private LocalDateTime loaddate;
    private String udep;
    private Double fundaccont;
    private Double receipt;
    private Double fundacctot;
    private Double receiptot;
    private String loc;
    private String riskasscd;
    private String rm;
    private String pm;
    private Double fundaccrec;
    private String adminleader;
    private String techleader;
    private String leader;
    private String progress;
    private String cashadmin;
    private String timetask;
    private String contracttp;

    // Constructors

    /** default constructor */
    public MaContractinfoB() {
    }

    /** minimal constructor */
    public MaContractinfoB(String contractcd) {
        this.contractcd = contractcd;
    }

    /** full constructor */
    public MaContractinfoB(String contractcd, MaDepartmentB maDepartmentB, Double contractid, String contractnm,
            String partya, String deputycontract, String prjtype, Double fundt, String bustype, String contractstatus,
            Double contractyear, String fundratio, LocalDateTime signdate, String prj, LocalDateTime loaddate,
            String udep, Double fundaccont, Double receipt, Double fundacctot, Double receiptot, String loc,
            String riskasscd, String rm, String pm, Double fundaccrec, String adminleader, String techleader,
            String leader, String progress, String cashadmin, String timetask, String contracttp) {
        this.contractcd = contractcd;
        this.maDepartmentB = maDepartmentB;
        this.contractid = contractid;
        this.contractnm = contractnm;
        this.partya = partya;
        this.deputycontract = deputycontract;
        this.prjtype = prjtype;
        this.fundt = fundt;
        this.bustype = bustype;
        this.contractstatus = contractstatus;
        this.contractyear = contractyear;
        this.fundratio = fundratio;
        this.signdate = signdate;
        this.prj = prj;
        this.loaddate = loaddate;
        this.udep = udep;
        this.fundaccont = fundaccont;
        this.receipt = receipt;
        this.fundacctot = fundacctot;
        this.receiptot = receiptot;
        this.loc = loc;
        this.riskasscd = riskasscd;
        this.rm = rm;
        this.pm = pm;
        this.fundaccrec = fundaccrec;
        this.adminleader = adminleader;
        this.techleader = techleader;
        this.leader = leader;
        this.progress = progress;
        this.cashadmin = cashadmin;
        this.timetask = timetask;
        this.contracttp = contracttp;
    }

    // Property accessors
    @Id

    @Column(name = "CONTRACTCD", unique = true, nullable = false)

    public String getContractcd() {
        return this.contractcd;
    }

    public void setContractcd(String contractcd) {
        this.contractcd = contractcd;
    }

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "DEPID")

    public MaDepartmentB getMaDepartmentB() {
        return this.maDepartmentB;
    }

    public void setMaDepartmentB(MaDepartmentB maDepartmentB) {
        this.maDepartmentB = maDepartmentB;
    }

    @Column(name = "CONTRACTID", precision = 38, scale = 8)

    public Double getContractid() {
        return this.contractid;
    }

    public void setContractid(Double contractid) {
        this.contractid = contractid;
    }

    @Column(name = "CONTRACTNM")

    public String getContractnm() {
        return this.contractnm;
    }

    public void setContractnm(String contractnm) {
        this.contractnm = contractnm;
    }

    @Column(name = "PARTYA")

    public String getPartya() {
        return this.partya;
    }

    public void setPartya(String partya) {
        this.partya = partya;
    }

    @Column(name = "DEPUTYCONTRACT")

    public String getDeputycontract() {
        return this.deputycontract;
    }

    public void setDeputycontract(String deputycontract) {
        this.deputycontract = deputycontract;
    }

    @Column(name = "PRJTYPE")

    public String getPrjtype() {
        return this.prjtype;
    }

    public void setPrjtype(String prjtype) {
        this.prjtype = prjtype;
    }

    @Column(name = "FUNDT", precision = 38, scale = 8)

    public Double getFundt() {
        return this.fundt;
    }

    public void setFundt(Double fundt) {
        this.fundt = fundt;
    }

    @Column(name = "BUSTYPE")

    public String getBustype() {
        return this.bustype;
    }

    public void setBustype(String bustype) {
        this.bustype = bustype;
    }

    @Column(name = "CONTRACTSTATUS")

    public String getContractstatus() {
        return this.contractstatus;
    }

    public void setContractstatus(String contractstatus) {
        this.contractstatus = contractstatus;
    }

    @Column(name = "CONTRACTYEAR", precision = 38, scale = 8)

    public Double getContractyear() {
        return this.contractyear;
    }

    public void setContractyear(Double contractyear) {
        this.contractyear = contractyear;
    }

    @Column(name = "FUNDRATIO")

    public String getFundratio() {
        return this.fundratio;
    }

    public void setFundratio(String fundratio) {
        this.fundratio = fundratio;
    }

    @Column(name = "SIGNDATE", length = 11)

    public LocalDateTime getSigndate() {
        return this.signdate;
    }

    public void setSigndate(LocalDateTime signdate) {
        this.signdate = signdate;
    }

    @Column(name = "PRJ")

    public String getPrj() {
        return this.prj;
    }

    public void setPrj(String prj) {
        this.prj = prj;
    }

    @Column(name = "LOADDATE", length = 11)

    public LocalDateTime getLoaddate() {
        return this.loaddate;
    }

    public void setLoaddate(LocalDateTime loaddate) {
        this.loaddate = loaddate;
    }

    @Column(name = "UDEP")

    public String getUdep() {
        return this.udep;
    }

    public void setUdep(String udep) {
        this.udep = udep;
    }

    @Column(name = "FUNDACCONT", precision = 38, scale = 8)

    public Double getFundaccont() {
        return this.fundaccont;
    }

    public void setFundaccont(Double fundaccont) {
        this.fundaccont = fundaccont;
    }

    @Column(name = "RECEIPT", precision = 38, scale = 8)

    public Double getReceipt() {
        return this.receipt;
    }

    public void setReceipt(Double receipt) {
        this.receipt = receipt;
    }

    @Column(name = "FUNDACCTOT", precision = 38, scale = 8)

    public Double getFundacctot() {
        return this.fundacctot;
    }

    public void setFundacctot(Double fundacctot) {
        this.fundacctot = fundacctot;
    }

    @Column(name = "RECEIPTOT", precision = 38, scale = 8)

    public Double getReceiptot() {
        return this.receiptot;
    }

    public void setReceiptot(Double receiptot) {
        this.receiptot = receiptot;
    }

    @Column(name = "LOC")

    public String getLoc() {
        return this.loc;
    }

    public void setLoc(String loc) {
        this.loc = loc;
    }

    @Column(name = "RISKASSCD")

    public String getRiskasscd() {
        return this.riskasscd;
    }

    public void setRiskasscd(String riskasscd) {
        this.riskasscd = riskasscd;
    }

    @Column(name = "RM")

    public String getRm() {
        return this.rm;
    }

    public void setRm(String rm) {
        this.rm = rm;
    }

    @Column(name = "PM")

    public String getPm() {
        return this.pm;
    }

    public void setPm(String pm) {
        this.pm = pm;
    }

    @Column(name = "FUNDACCREC", precision = 38, scale = 8)

    public Double getFundaccrec() {
        return this.fundaccrec;
    }

    public void setFundaccrec(Double fundaccrec) {
        this.fundaccrec = fundaccrec;
    }

    @Column(name = "ADMINLEADER")

    public String getAdminleader() {
        return this.adminleader;
    }

    public void setAdminleader(String adminleader) {
        this.adminleader = adminleader;
    }

    @Column(name = "TECHLEADER")

    public String getTechleader() {
        return this.techleader;
    }

    public void setTechleader(String techleader) {
        this.techleader = techleader;
    }

    @Column(name = "LEADER", length = 20)

    public String getLeader() {
        return this.leader;
    }

    public void setLeader(String leader) {
        this.leader = leader;
    }

    @Column(name = "PROGRESS", length = 1000)

    public String getProgress() {
        return this.progress;
    }

    public void setProgress(String progress) {
        this.progress = progress;
    }

    @Column(name = "CASHADMIN", length = 20)

    public String getCashadmin() {
        return this.cashadmin;
    }

    public void setCashadmin(String cashadmin) {
        this.cashadmin = cashadmin;
    }

    @Column(name = "TIMETASK", length = 2000)

    public String getTimetask() {
        return this.timetask;
    }

    public void setTimetask(String timetask) {
        this.timetask = timetask;
    }

    @Column(name = "CONTRACTTP", length = 50)

    public String getContracttp() {
        return this.contracttp;
    }

    public void setContracttp(String contracttp) {
        this.contracttp = contracttp;
    }

    /**
     * toString
     *
     * @return String
     */
    @Override
    public String toString() {
        StringBuffer buffer = new StringBuffer();

        buffer.append(getClass().getName()).append("@").append(Integer.toHexString(hashCode())).append(" [");
        buffer.append("contractcd").append("='").append(getContractcd()).append("' ");
        buffer.append("maDepartmentB").append("='").append(getMaDepartmentB()).append("' ");
        buffer.append("contractid").append("='").append(getContractid()).append("' ");
        buffer.append("contractnm").append("='").append(getContractnm()).append("' ");
        buffer.append("partya").append("='").append(getPartya()).append("' ");
        buffer.append("deputycontract").append("='").append(getDeputycontract()).append("' ");
        buffer.append("prjtype").append("='").append(getPrjtype()).append("' ");
        buffer.append("fundt").append("='").append(getFundt()).append("' ");
        buffer.append("bustype").append("='").append(getBustype()).append("' ");
        buffer.append("contractstatus").append("='").append(getContractstatus()).append("' ");
        buffer.append("contractyear").append("='").append(getContractyear()).append("' ");
        buffer.append("fundratio").append("='").append(getFundratio()).append("' ");
        buffer.append("signdate").append("='").append(getSigndate()).append("' ");
        buffer.append("prj").append("='").append(getPrj()).append("' ");
        buffer.append("loaddate").append("='").append(getLoaddate()).append("' ");
        buffer.append("udep").append("='").append(getUdep()).append("' ");
        buffer.append("fundaccont").append("='").append(getFundaccont()).append("' ");
        buffer.append("receipt").append("='").append(getReceipt()).append("' ");
        buffer.append("fundacctot").append("='").append(getFundacctot()).append("' ");
        buffer.append("receiptot").append("='").append(getReceiptot()).append("' ");
        buffer.append("loc").append("='").append(getLoc()).append("' ");
        buffer.append("riskasscd").append("='").append(getRiskasscd()).append("' ");
        buffer.append("rm").append("='").append(getRm()).append("' ");
        buffer.append("pm").append("='").append(getPm()).append("' ");
        buffer.append("fundaccrec").append("='").append(getFundaccrec()).append("' ");
        buffer.append("adminleader").append("='").append(getAdminleader()).append("' ");
        buffer.append("techleader").append("='").append(getTechleader()).append("' ");
        buffer.append("leader").append("='").append(getLeader()).append("' ");
        buffer.append("progress").append("='").append(getProgress()).append("' ");
        buffer.append("cashadmin").append("='").append(getCashadmin()).append("' ");
        buffer.append("timetask").append("='").append(getTimetask()).append("' ");
        buffer.append("contracttp").append("='").append(getContracttp()).append("' ");
        buffer.append("]");

        return buffer.toString();
    }

}

部门实体

import java.util.HashSet;
import java.util.Set;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;

@Entity
@Table(name = "MA_DEPARTMENT_B")

public class MaDepartmentB implements java.io.Serializable {

    // Fields

    private Long id;
    private String name;
    private String leader;
    private Set<MaContractinfoB> maContractinfoBs = new HashSet<MaContractinfoB>(0);
    private Set<MaContraimB> maContraimBs = new HashSet<MaContraimB>(0);

    // Constructors

    /** default constructor */
    public MaDepartmentB() {
    }

    /** minimal constructor */
    public MaDepartmentB(Long id) {
        this.id = id;
    }

    /** full constructor */
    public MaDepartmentB(Long id, String name, String leader, Set<MaContractinfoB> maContractinfoBs,
            Set<MaContraimB> maContraimBs) {
        this.id = id;
        this.name = name;
        this.leader = leader;
        this.maContractinfoBs = maContractinfoBs;
        this.maContraimBs = maContraimBs;
    }

    // Property accessors
    @Id

    @Column(name = "ID", unique = true, nullable = false, precision = 10, scale = 0)

    public Long getId() {
        return this.id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    @Column(name = "NAME")

    public String getName() {
        return this.name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Column(name = "LEADER")

    public String getLeader() {
        return this.leader;
    }

    public void setLeader(String leader) {
        this.leader = leader;
    }

    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "maDepartmentB")

    public Set<MaContractinfoB> getMaContractinfoBs() {
        return this.maContractinfoBs;
    }

    public void setMaContractinfoBs(Set<MaContractinfoB> maContractinfoBs) {
        this.maContractinfoBs = maContractinfoBs;
    }

    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "maDepartmentB")

    public Set<MaContraimB> getMaContraimBs() {
        return this.maContraimBs;
    }

    public void setMaContraimBs(Set<MaContraimB> maContraimBs) {
        this.maContraimBs = maContraimBs;
    }

    /**
     * toString
     *
     * @return String
     */
    @Override
    public String toString() {
        StringBuffer buffer = new StringBuffer();

        buffer.append(getClass().getName()).append("@").append(Integer.toHexString(hashCode())).append(" [");
        buffer.append("id").append("='").append(getId()).append("' ");
        buffer.append("name").append("='").append(getName()).append("' ");
        buffer.append("leader").append("='").append(getLeader()).append("' ");
        buffer.append("maContractinfoBs").append("='").append(getMaContractinfoBs()).append("' ");
        buffer.append("maContraimBs").append("='").append(getMaContraimBs()).append("' ");
        buffer.append("]");

        return buffer.toString();
    }

}

jparepository

public interface MaContractinfoBRepository extends JpaRepository<MaContractinfoB, Long> {
    @Query("from MaContractinfoB c join fetch c.maDepartmentB")
    List<MaContractinfoB> findAll();

    @Query("select contractnm from MaContractinfoB")
    List<String> findAllName();

//    @Query("from MaContractinfoB c join fetch c.maDepartmentB")
//    List test();
}

在MaContractinfoBRepository中，当我使用findAllName函数时，它将立即在0.05秒内返回1000个合同名称。当我使用findAll时，即使我添加了join fetch，使用部门实体获取1000个数据也将花费15s。但是，如果我通过诸如navicat之类的db工具中的本机sql得到它，它将仅花费0.07s。

我错过了任何关键点吗？如何查询MaContractinfoB表不那么慢？

Answer 1

之所以发生这种情况，是因为在内部使用'fetch'命令时，hibernate还在每次调用findAll（）方法时都懒惰地加载每个Contract ID的Department实体的所有行。因此，如果部门中有1个合同的n行且总共有m个合同，则对数据库的调用总数将为'm * n'。

解决此问题的一种方法是使用DTO投影。数据传输对象是一种在一个查询中定义所有必需列并一次访问数据库的简便方法。

我发现本文很有用，它显示了编写DTO投影的多种方法。https://thoughts-on-java.org/dto-projections/

提到的一种方法是：使用JPQL，您可以使用构造函数表达式来定义构造函数调用，其关键字为new，后跟DTO的完全分类的类名以及大括号中的构造函数参数列表。像这样的东西：

TypedQuery<ContractWithDepartmentDetails> q = em.createQuery(
        "SELECT new com.practice.model.ContractWithDepartmentDetails(c.id, c.name, d.name) FROM contract c JOIN c.department d",
        ContractWithDepartmentDetails.class);