休眠：自我加入混乱？ [英] Hibernate : self join confusion?
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问题描述
我有一个
类别表。其中前5个是主类别，
其他类别是子类别。
我需要抓取前5个主类别的子类别，所以我已经找到了SQL查询
SELECT m.category_id，m.category_name AS'Parent '，
e.category_name AS'Sub'
FROM category e
INNER JOIN category m ON m.category_id = e.parent_category_id
ORDER BY Parent
查询加入同一个表本身，并得到下面给出的结果
结果
如何将SQL查询转换为HQL并返回上述数据image to user in
standard json format？
FetchSubCategory
import java.io.Serializable;
import java.util.Set;
import javax.persistence。*;
@Entity
@Table（name =category）
public class FetchSubCategory implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue（strategy = GenerationType.IDENTITY）
@Column（name =category_id）
private Integer categoryId;
@Column（name =category_name）
private String categoryName;
@ManyToOne（cascade = {CascadeType.ALL}）
@JoinColumn（name =parent_category_id）
private FetchSubCategory parent;
@OneToMany（mappedBy =parent）
private设置< FetchSubCategory>子类别;
public Integer getCategoryId（）{
return categoryId;
}
public void setCategoryId（Integer categoryId）{
this.categoryId = categoryId;
}
public String getCategoryName（）{
return categoryName;
}
public void setCategoryName（String categoryName）{
this.categoryName = categoryName;
}
public FetchSubCategory getParent（）{
return parent;
}
public void setParent（FetchSubCategory parent）{
this.parent = parent;
}
public Set< FetchSubCategory> getSubCategory（）{
return subCategory;
}
public void setSubCategory（Set< FetchSubCategory> subCategory）{
this.subCategory = subCategory;
}
}
方法
public Set< FetchSubCategory> fetchSubCategory（）抛出SQLException，ClassNotFoundException，IOException {
Set< FetchSubCategory> groupList = null;
尝试{
Session session = sessionFactory.getCurrentSession（）;
Query query = session.createQuery（SELECT m.categoryName AS'Parent'，e.categoryName AS'Sub'FROM FetchSubCategory e INNER JOIN FetchSubCategory m ORDER BY Parent）;
groupList =（Set< FetchSubCategory>）query.list（）;
} catch（Exception e）{
e.printStackTrace（）;
}
返回groupList;
}
任何人都可以改正我的错误并告诉我如何获取如上图所示的结果？ 将解决您的问题
@Entity
@Table（name =category ）
public class FetchSubCategory implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue（strategy = GenerationType.IDENTITY）
@Column（name =category_id）
private Integer categoryId;
@Column（name =category_name）
private String categoryName;
@NotFound（action = NotFoundAction.IGNORE）
@ManyToOne
@JsonIgnore
@JoinColumn（name =parent_category_id）
private FetchSubCategory mainCategory;
@JsonSerialize（include = JsonSerialize.Inclusion.NON_EMPTY）//避免空json arrays.objects
@OneToMany（mappedBy =mainCategory，fetch = FetchType.EAGER）
私人列表< FetchSubCategory>子类别;
public Integer getCategoryId（）{
return categoryId;
}
public void setCategoryId（Integer categoryId）{
this.categoryId = categoryId;
}
public String getCategoryName（）{
return categoryName;
}
public void setCategoryName（String categoryName）{
this.categoryName = categoryName;
}
public FetchSubCategory getMainCategory（）{
return mainCategory;
}
public void setMainCategory（FetchSubCategory mainCategory）{
this.mainCategory = mainCategory;
}
公开列表< FetchSubCategory> getSubCategory（）{
return subCategory;
}
public void setSubCategory（List< FetchSubCategory> subCategory）{
this.subCategory = subCategory;
}
获取您的子类别
public List< FetchSubCategory> fetchSubCategory（）抛出SQLException，ClassNotFoundException，IOException {
List< FetchSubCategory> groupList = null;
尝试{
Session session = sessionFactory.getCurrentSession（）;
Query query = session.createQuery（select distinct FROM FROM FetchSubCategory e INNER JOIN e.subCategory m ORDER BY m.mainCategory）;
groupList = query.list（）;
} catch（Exception e）{
e.printStackTrace（）;
}
返回groupList;
}
I have a
categorytable.In which first 5 are main category and others are sub category.
I need to fetch the sub categories of first 5 main category so i have found the sql query
SELECT m.category_id,m.category_name AS 'Parent',
e.category_name AS 'Sub'
FROM category e
INNER JOIN category m ON m.category_id = e.parent_category_id
ORDER BY Parent
The query is joining the same table itself.and am getting the result given below
Result
How can i convert the SQL query to HQL and return the data like above image to user in standard json format ?
FetchSubCategory
import java.io.Serializable;
import java.util.Set;
import javax.persistence.*;
@Entity
@Table(name = "category")
public class FetchSubCategory implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "category_id")
private Integer categoryId;
@Column(name = "category_name")
private String categoryName;
@ManyToOne(cascade = {CascadeType.ALL})
@JoinColumn(name = "parent_category_id")
private FetchSubCategory parent;
@OneToMany(mappedBy = "parent")
private Set<FetchSubCategory> subCategory;
public Integer getCategoryId() {
return categoryId;
}
public void setCategoryId(Integer categoryId) {
this.categoryId = categoryId;
}
public String getCategoryName() {
return categoryName;
}
public void setCategoryName(String categoryName) {
this.categoryName = categoryName;
}
public FetchSubCategory getParent() {
return parent;
}
public void setParent(FetchSubCategory parent) {
this.parent = parent;
}
public Set<FetchSubCategory> getSubCategory() {
return subCategory;
}
public void setSubCategory(Set<FetchSubCategory> subCategory) {
this.subCategory = subCategory;
}
}
Method
public Set<FetchSubCategory> fetchSubCategory() throws SQLException, ClassNotFoundException, IOException {
Set<FetchSubCategory> groupList = null;
try {
Session session = sessionFactory.getCurrentSession();
Query query = session.createQuery("SELECT m.categoryName AS 'Parent', e.categoryName AS 'Sub' FROM FetchSubCategory e INNER JOIN FetchSubCategory m ORDER BY Parent");
groupList = (Set<FetchSubCategory>) query.list();
} catch (Exception e) {
e.printStackTrace();
}
return groupList;
}
Can any one please correct my mistake and tell me how to fetch result like above image?
解决方案
This stuff will solve your problem
@Entity
@Table(name = "category")
public class FetchSubCategory implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "category_id")
private Integer categoryId;
@Column(name = "category_name")
private String categoryName;
@NotFound(action = NotFoundAction.IGNORE)
@ManyToOne
@JsonIgnore
@JoinColumn(name = "parent_category_id")
private FetchSubCategory mainCategory;
@JsonSerialize(include = JsonSerialize.Inclusion.NON_EMPTY)//Avoiding empty json arrays.objects
@OneToMany(mappedBy = "mainCategory", fetch = FetchType.EAGER)
private List<FetchSubCategory> subCategory;
public Integer getCategoryId() {
return categoryId;
}
public void setCategoryId(Integer categoryId) {
this.categoryId = categoryId;
}
public String getCategoryName() {
return categoryName;
}
public void setCategoryName(String categoryName) {
this.categoryName = categoryName;
}
public FetchSubCategory getMainCategory() {
return mainCategory;
}
public void setMainCategory(FetchSubCategory mainCategory) {
this.mainCategory = mainCategory;
}
public List<FetchSubCategory> getSubCategory() {
return subCategory;
}
public void setSubCategory(List<FetchSubCategory> subCategory) {
this.subCategory = subCategory;
}
Get your sub categories
public List<FetchSubCategory> fetchSubCategory() throws SQLException, ClassNotFoundException, IOException {
List<FetchSubCategory> groupList = null;
try {
Session session = sessionFactory.getCurrentSession();
Query query = session.createQuery("select distinct e FROM FetchSubCategory e INNER JOIN e.subCategory m ORDER BY m.mainCategory");
groupList = query.list();
} catch (Exception e) {
e.printStackTrace();
}
return groupList;
}
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