“无法编写JSON：无法懒惰地初始化角色集合”，使用springboot和休眠搜索

Question

我正在尝试在两个实体之间建立Many-to-Many关系：

import com.fasterxml.jackson.annotation.JsonIgnore;
import com.perso.ez.debate.tag.TagEntity;
import org.hibernate.search.annotations.Field;
import org.hibernate.search.annotations.Indexed;
import org.hibernate.search.annotations.IndexedEmbedded;

import javax.persistence.*;
import java.time.LocalDateTime;
import java.util.List;

@Entity
@Indexed
@Table(name = "data")
public class DataLightEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @Field
    @Column(name = "title")
    private String title;

    @Field
    @Column(name = "subtitle")
    private String subtitle;

    @Field
    @Column(name = "text", columnDefinition = "TEXT")
    private String text;

    @IndexedEmbedded
    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(name = "data_tags", joinColumns = @JoinColumn(name = "data_id", referencedColumnName = "id"), inverseJoinColumns = @JoinColumn(name = "tag_id", referencedColumnName = "id"))
    private List<TagEntity> tags;

    @Column(name = "icon")
    private String icon;

    @Column(name = "date")
    private LocalDateTime date = LocalDateTime.now();

    public Long getId() {
        return id;
    }

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

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getSubtitle() {
        return subtitle;
    }

    public void setSubtitle(String subtitle) {
        this.subtitle = subtitle;
    }

    public String getText() {
        return text;
    }

    public void setText(String text) {
        this.text = text;
    }

    public String getIcon() {
        return icon;
    }

    public void setIcon(String icon) {
        this.icon = icon;
    }

    public LocalDateTime getDate() {
        return date;
    }

    public void setDate(LocalDateTime date) {
        this.date = date;
    }

    public List<TagEntity> getTags() {
        return tags;
    }

    public void setTags(List<TagEntity> tags) {
        this.tags = tags;
    }

    @Override
    public String toString() {
        return "DataLightEntity{" +
                "id=" + id +
                ", title='" + title + '\'' +
                ", subtitle='" + subtitle + '\'' +
                ", text='" + text + '\'' +
                ", tags=" + tags +
                ", icon='" + icon + '\'' +
                ", date=" + date +
                '}';
    }
}

package com.perso.ez.debate.tag;

import com.fasterxml.jackson.annotation.JsonBackReference;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.perso.ez.debate.data.DataLightEntity;
import com.perso.ez.debate.tag.type.TagTypeEntity;
import org.hibernate.search.annotations.Field;

import javax.persistence.*;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;

@Entity
@Table(name = "tag")
public class TagEntity implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @Field
    @Column(name = "tag")
    private String tag;

    @ManyToOne
    @JoinColumn(name = "type_id", nullable = false)
    private TagTypeEntity type;

    @ManyToMany(mappedBy = "tags")
    @JsonIgnore
    private List<DataLightEntity> datas = new ArrayList<>();

    public String getTag() {
        return tag;
    }

    public void setTag(String tag) {
        this.tag = tag;
    }

    public Long getId() {
        return id;
    }

    public TagTypeEntity getType() {
        return type;
    }

    public void setType(TagTypeEntity type) {
        this.type = type;
    }

    public List<DataLightEntity> getDatas() {
        return datas;
    }

    public void setDatas(List<DataLightEntity> datas) {
        this.datas = datas;
    }
}

我将@Field和@IndexedEmbedded注释用于我的研究功能，并使用@JsonIgnore以避免无限循环。

但是，当我尝试进行研究时，仍然出现此错误：

Resolved [org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: failed to lazily initialize a collection of role: com.perso.ez.debate.data.DataLightEntity.tags, could not initialize proxy - no Session; nested exception is com.fasterxml.jackson.databind.JsonMappingException: failed to lazily initialize a collection of role: com.perso.ez.debate.data.DataLightEntity.tags, could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]->com.perso.ez.debate.data.DataLightEntity["tags"])]

我不知道该怎么办。我尝试了很多事情，但是我没有主意。如果有人有想法，那对我会有很大帮助。谢谢！

Answer 1

如下添加fetch: Lazy到您的DataLightEntity：

@IndexedEmbedded
    @ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinTable(name = "data_tags", joinColumns = @JoinColumn(name = "data_id", referencedColumnName = "id"), inverseJoinColumns = @JoinColumn(name = "tag_id", referencedColumnName = "id"))
    private List<TagEntity> tags;

Answer 2

我认为，由于您懒惰地获取（默认情况下），然后在对结果集进行反序列化时，出现了该错误。要克服这些问题，请将其添加到延迟获取实体（在这种情况下，由于您具有多对多关系，请在@Table annotation和DataLightEntity类中的TagEntity之后为实体类级别都添加此行）

@JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})

希望这会有所帮助。