Question

我正在尝试使用此查询通过Hibernate查询大量实体：

        "Select * " +
        " From Dossier as dossier" +
        " LEFT  JOIN FETCH dossier.candidat as candidat " +
        " LEFT  JOIN FETCH candidat.roles as role " +
        " LEFT  JOIN FETCH dossier.infoPerso as infoPerso " +
        " LEFT  JOIN FETCH dossier.etablissementOrigine as etablissementOrigine " +
        " LEFT  JOIN FETCH etablissementOrigine.filieres as filieres " +
        " LEFT OUTER JOIN FETCH etablissementOrigine.ville as villeOrigine " +
        " LEFT  JOIN FETCH dossier.etatDossier as etatDossier " +
        " LEFT OUTER JOIN FETCH infoPerso.fichierCNIRecto as fichierCNIRecto " +
        " LEFT OUTER JOIN FETCH fichierCNIRecto.type " +
        " LEFT OUTER JOIN FETCH infoPerso.fichierCNIVerso as fichierCNIVerso " +
        " LEFT OUTER JOIN FETCH fichierCNIVerso.type " +
        " LEFT OUTER JOIN FETCH infoPerso.fichierCV as fichierCV " +
        " LEFT OUTER JOIN FETCH fichierCV.type " +
        " LEFT OUTER JOIN FETCH infoPerso.fichierJAPD as fichierJAPD " +
        " LEFT OUTER JOIN FETCH fichierJAPD.type " +
        " LEFT OUTER JOIN FETCH infoPerso.fichierCNIVerso as fichierCNIVerso " +
        " LEFT OUTER JOIN FETCH fichierCNIVerso.type " +
        " LEFT OUTER JOIN FETCH infoPerso.situationFamilliale as situation "


            dossiers = getEntityManager()
                    .createQuery(sql, Dossier.class)
                    .getResultList();

我可以看到hibernate在做第一个大的本机SQL查询。但就在那之后，Hibernate为每一行生成了1个以上的查询来加载DOssier，我不知道为什么，Dossier已经是fetchs元素的一部分......

 /* load org.ema.ecandidature.dossier.Dossier */ select
    dossier0_.id as id1_61_0_,
    dossier0_.version as version2_61_0_,
    dossier0_.valid as valid3_61_0_,
    dossier0_.validSecretariat as validSec4_61_0_,
    dossier0_.candidat_id as candidat7_17_0_,
    dossier0_.casParticulier as casParti1_17_0_,
    dossier0_.dateInscription as dateInsc2_17_0_,
    dossier0_.dateSoumission as dateSoum3_17_0_,
    dossier0_.entreprise_id as entrepri8_17_0_,
    dossier0_.etablissementOrigine_id as etabliss9_17_0_,
    dossier0_.etatDossier_id as etatDos10_17_0_,
    dossier0_.infoPaiement_id as infoPai11_17_0_,
    dossier0_.infoPerso_id as infoPer12_17_0_,
    dossier0_.listCursusAcademique_id as listCur13_17_0_,
    dossier0_.listDocumentsSupplementaires_id as listDoc14_17_0_,
    dossier0_.listExpEntreprise_id as listExp15_17_0_,
    dossier0_.listFormations_id as listFor16_17_0_,
    dossier0_.listLangues_id as listLan17_17_0_,
    dossier0_.listReferents_id as listRef18_17_0_,
    dossier0_.listSejourEtranger_id as listSej19_17_0_,
    dossier0_.motivationCentreInteret_id as motivat20_17_0_,
    dossier0_.secretariatChangeDate as secretar4_17_0_,
    dossier0_.secretariatChangeDateBackup as secretar5_17_0_,
    dossier0_.validationCommentaire as validati6_17_0_ 
from
    Dossier dossier0_ 
where
    dossier0_.candidat_id=?

Dossier.class：

@Entity
@BatchSize(size=100)
public class Dossier extends ValidableEntity {

    /** The Constant serialVersionUID. */
    private static final long serialVersionUID = 1L;

    /** The etablissement origine. */
    @SecretaryExport
    @ManyToOne( fetch=FetchType.LAZY)
    @JoinColumn()
    private Etablissement etablissementOrigine;

    /** The date inscription. */
    @SecretaryExport
    private Date dateInscription;

    /** The date soumission. */
    @SecretaryExport
    private Date dateSoumission;

    /** The date modification. */
    @SecretaryExport
    private Date secretariatChangeDate;

    /** The date de modification backup. */
    @SecretaryExport
    private Date secretariatChangeDateBackup;

    /** The cas particulier. */
    @SecretaryExport
    private Boolean casParticulier;

    /** The etat dossier. */
    @SecretaryExport
    @ManyToOne( fetch=FetchType.LAZY)
    @JoinColumn()
    private EtatDossier etatDossier;

    /** The candidat. */
    @SecretaryExport
    @OneToOne(fetch=FetchType.LAZY)
    private Candidat candidat;

    /** The info perso. */
    @SecretaryExport
    @Obligatoire
    @ObligatoireSecretariat
    @OneToOne(cascade = { CascadeType.ALL },fetch=FetchType.LAZY,orphanRemoval = true)
    private InfoPerso infoPerso;

    /** The list formations. */
    //@SecretaryExport
    @Obligatoire
    @ObligatoireSecretariat
    @OneToOne(cascade = { CascadeType.ALL },fetch=FetchType.LAZY,orphanRemoval = true)
    private ListFormations listFormations;

    /** The list cursus academique. */
    @SecretaryExport
    @Obligatoire
    @ObligatoireSecretariat
    @OneToOne(cascade = { CascadeType.ALL },fetch=FetchType.LAZY,orphanRemoval = true)
    private ListCursusAcademique listCursusAcademique;

    /** The motivation centre interet. */
    @SecretaryExport
    @Obligatoire
    @ObligatoireSecretariat
    @OneToOne(cascade = { CascadeType.ALL },fetch=FetchType.LAZY,orphanRemoval = true)
    private MotivationCentreInteret motivationCentreInteret;

    /** The entreprise. */
    @SecretaryExport
    @Obligatoire
    @ObligatoireSecretariat
    @OneToOne(cascade = { CascadeType.ALL },fetch=FetchType.LAZY,orphanRemoval = true)
    private Entreprise entreprise;

    /** The list langues. */
    @SecretaryExport
    @Obligatoire
    @ObligatoireSecretariat
    @OneToOne(cascade = { CascadeType.ALL },fetch=FetchType.LAZY,orphanRemoval = true)
    private ListLangues listLangues;

    /** The list sejour etranger. */
    @SecretaryExport
    @Obligatoire
    @ObligatoireSecretariat
    @OneToOne(cascade = { CascadeType.ALL },fetch=FetchType.LAZY,orphanRemoval = true)
    private ListSejourEtranger listSejourEtranger;

    /** The list exp entreprise. */
    @SecretaryExport
    @Obligatoire
    @ObligatoireSecretariat
    @OneToOne(cascade = { CascadeType.ALL },fetch=FetchType.LAZY,orphanRemoval = true)
    private ListExpEntreprise listExpEntreprise;

    /** The list referents. */
    @SecretaryExport
    @Obligatoire
    @ObligatoireSecretariat
    @OneToOne(cascade = { CascadeType.ALL},fetch=FetchType.LAZY,orphanRemoval = true)
    private ListReferents listReferents;

    /** The info paiement. */
    @SecretaryExport
    @Obligatoire
    @ObligatoireSecretariat
    @OneToOne(cascade = { CascadeType.ALL},fetch=FetchType.LAZY,orphanRemoval = true)
    private InfoPaiement infoPaiement;

    /** The avis jury. */
    @OneToMany(mappedBy= "dossier" , cascade = { CascadeType.ALL},fetch=FetchType.LAZY,orphanRemoval = true)
    private Set<AvisJury> avisJury = new HashSet<>();

    /** The list documents supplementaires. */
    @Obligatoire
    @ObligatoireSecretariat
    @OneToOne(cascade = { CascadeType.ALL },fetch=FetchType.LAZY,orphanRemoval = true)
    private ListDocumentsSupplementaires listDocumentsSupplementaires;

    /** The list fichier. */
    @OneToMany(mappedBy = "dossier", cascade = { CascadeType.ALL },fetch=FetchType.LAZY,orphanRemoval = true)
    private Set<Fichier> listFichier;

    /** The list avis examinateur. */
    @OneToMany(mappedBy= "dossier" , cascade = { CascadeType.ALL},fetch=FetchType.LAZY,orphanRemoval = true)
    private Set<AvisExaminateur> listAvisExaminateur;

    /** The list commentaire. */
    @OneToMany(cascade = { CascadeType.ALL},fetch=FetchType.LAZY,orphanRemoval = true)
    private Set<Commentaire> listCommentaire;

    /** The validation commentaire. */
    @Column(length = 500)
    @Pattern(regexp="^(.|\n|\r|\t)*$")//accepte tous les caractères et les retours lignes
    private String validationCommentaire;

}

这有什么问题？

Answer 1

这有什么问题？

正如我在我的书High-Performance Java Persistence中所解释的那样，除非您打算修改实体，否则永远不应该获取实体。因此，如果您只需要一个只读视图，那么您应该使用DTO projection instead。

假设您确实需要获取整个图表，因为您计划对其进行修改，那么您必须使用以下提取策略：

您可以在第一个查询中获取尽可能多的子@OneToOne和@ManyToOne实体关联，也可以在AT @OneToMany或@ManyToMany中获取。

对于剩余的@OneToMany或@ManyToMany，您必须使用辅助查询。但是，您不希望在N+1 fashion中执行此操作，因此您需要在传递使用第一个查询获取的根实体时运行JPQL查询。

请记住，如果将二级集合重新组合到根实体上，则会在根实体上触发一些不需要的修改。因此，如果您想将根实体传递给Web层，那么您应该以只读模式获取它们。

同样，如果您不需要实体，那么您应该只需获取DTO投影并使用ResultTransfomer将表格式投影转换为DTO图表，如{{3 }}

但就在那之后，Hibernate为每一行生成了1个查询加载DOssier，我不知道为什么，Dossier已经是fetchs的一部分了元件...

从这些映射中，不清楚为什么会执行该查询，但您可以在this article在Hibernate中轻松调试它，并查看堆栈跟踪以查看触发的内容它

Answer 2

我猜想还会发出其他查询，因为您正在对EAGER关联使用*ToOne提取，这是偶然的，因为这是*ToOne关联的默认提取策略。弗拉德（Vlad）提到的DTO方法是必经之路，但我知道，进行所有布线将需要大量工作。为了减少容易出错的样板代码，我只能建议您看看Blaze-Persistence Entity Views所提供的内容。

该库在JPA之上运行，并为您有效地处理DTO映射。您只需要将目标结构定义为接口即可。

您甚至可以使用不同的获取策略（JOIN，SELECT和SUBSELECT），就像Hibernate提供的按ID加载策略一样，但这可以用于任何类型的查询，而不仅仅是按ID。

Answer 3

我遇到了相同的行为。可以说您有大师班

@OneToMany
@Fetch(FetchMode.JOIN)
private List<Detail> details = new ArrayList<>();

使用此配置，如果我提取所有详细信息，休眠将首先执行select join，然后选择每个详细信息及其ID。解决方案是删除Master类中的@Fetch（FetchMode.JOIN）。

在同一实体

3 个答案: