java - 在同一实体上加入 FETCH 后 hibernate 额外查询

Question

我正在尝试使用以下查询通过 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 正在执行第一个大型原生 SQL 查询。但就在这之后，Hibernate 为每一行生成了 1 个查询来加载 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;

}

这有什么问题吗？

Answer 1

What is wrong with that?

除非您打算修改它们，否则不应获取实体。所以，如果你只需要一个只读 View ，那么你应该使用 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获取策略:

您可以在第一个查询中获取尽可能多的子 @OneToOne 和 @ManyToOne 实体关联以及最多一个 @OneToMany 或@ManyToMany。

对于剩余的@OneToMany 或@ManyToMany，您必须使用辅助查询。但是，您不想在 N+1 fashion 中执行此操作，因此您需要为这些查询运行 JPQL 查询，同时传递您使用第一个查询获取的根实体。

请记住，如果您将辅助集合重新组装到根实体上，您将触发对根实体进行一些不必要的修改。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，那么您应该只获取 DTO 投影并使用 ResultTransfomer 将类似表格的投影转换为 DTO 图形。

But just after that, Hibernate generates 1 more query for each row toload DOssier, I don't know why, Dossier is already a part of fetchselements...

从这些映射中，不清楚执行该查询的原因，但您可以在 datasource-proxy level 轻松调试它。 , 在 Hibernate 中查看堆栈跟踪以查看是什么触发了它。