Java 具有自反联想的HQL不'；行不通

我遇到了一个与自身相关的类的问题。对象是这样的：

Category.java

package com.borjabares.pan_ssh.model.category;

import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.SequenceGenerator;

import com.borjabares.pan_ssh.util.Trimmer;

@Entity
public class Category {
private long categoryId;
private String name;
private Category parent;

public Category() {
}

public Category(String name, Category parent) {
    this.name = name;
    this.parent = parent;
}

@SequenceGenerator(name = "CategoryIdGenerator", sequenceName = "CategorySeq")
@Id
@GeneratedValue(strategy = GenerationType.AUTO, generator = "CategoryIdGenerator")
public long getCategoryId() {
    return categoryId;
}

public void setCategoryId(long categoryId) {
    this.categoryId = categoryId;
}

public String getName() {
    return name;
}

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

@ManyToOne(optional=false, fetch=FetchType.EAGER) 
@JoinColumn(name="categoryId", insertable=false, updatable=false, nullable = true)
public Category getParent() {
    return parent;
}

public void setParent(Category parent) {
    this.parent = parent;
}

@Override
public String toString() {
    return "Category [\ncategoryId=" + categoryId + ", \nname=" + name
            + ", \nparent=" + parent + "]";
}
}

这种联系只有一个层次。插入，其他查询正在运行。但是，当我尝试仅选择父类别或非父类别时，Hibernate仅为父类别或表的所有结果返回0个结果

现在的查询是这样的，但是我有很多其他的带有连接的查询是空的，其他方法总是得到相同的结果

@SuppressWarnings("unchecked")
public List<Category> listParentCategories() {
    return getSession().createQuery(
            "SELECT c FROM Category c WHERE c.parent is null ORDER BY c.name")
            .list();
}

---

此外，在插入中，我控制类别只能是父类别或子类别，而类别不能是其自己的父类别。

您使用同一列（

categoryId

）唯一标识类别，并引用父类别。这不可能奏效，因为所有类别显然都将自己作为父类别。您需要另一列来保存父类别ID：

@Id
@SequenceGenerator(name = "CategoryIdGenerator", sequenceName = "CategorySeq")
@GeneratedValue(strategy = GenerationType.AUTO, generator = "CategoryIdGenerator")
@Column(name = "categoryId") // not necessary, but makes things clearer
public long getCategoryId() {
    return categoryId;
}

// optional must be true: some categories don't have a parent
@ManyToOne(optional = true, fetch = FetchType.EAGER) 
// insertable at least must be true if you want to create categories with a parent
@JoinColumn(name = "parentCategoryId", nullable = true)
public Category getParent() {
    return parent;
}

---

是，可选项必须为true（该死的复制粘贴）。但是，如果我删除insertable和updateable等于true，我就会在实体com.borjabares.pan_ssh.model.category.category列的映射中使用jUnit:org.hibernate.MappingException:Repeated列运行测试时出现此错误：categoryId（应该使用insert=“false”update=“false”映射）是的，这是主要问题，我在回答中指出：您使用ID列引用父类别，这显然是错误的。您必须使用另一个列名：

@JoinColumn（name=**“parentCategoryId”**，nullable=true）

哦，好吧，我搞错了，就是这样。非常感谢你！！我很困惑，因为插入工作正常，所以我错误地认为这与查询有关。

@Id
@SequenceGenerator(name = "CategoryIdGenerator", sequenceName = "CategorySeq")
@GeneratedValue(strategy = GenerationType.AUTO, generator = "CategoryIdGenerator")
@Column(name = "categoryId") // not necessary, but makes things clearer
public long getCategoryId() {
    return categoryId;
}

// optional must be true: some categories don't have a parent
@ManyToOne(optional = true, fetch = FetchType.EAGER) 
// insertable at least must be true if you want to create categories with a parent
@JoinColumn(name = "parentCategoryId", nullable = true)
public Category getParent() {
    return parent;
}