GROUP BY WITHOUT PROJECTION：这是不可能的，因为它是有道理的，在你可能找到的许多答案中，但大多数人不想使用投影，因为它要求他们每一个都投影属性，但要求是必须投影一个 bean。 （并作为结果返回）。在下面的示例中，我尝试将project 所需的bean 作为结果对象。
我相信我用一点技巧也达到了同样的结果，首先我试图在没有投影的情况下应用 group by，但我没有找到解决方案，所以我不得不依赖 Projection。
这是我想要实现的目标
select p.* FROM parent p INNER JOIN child c ON p.id_parent=c.id_father
WHERE c.child_name like '%?%' AND p.parent_name like '%?%'
group by p.id_parent
在 Java 代码中，我希望 p.* 成为 Parent 类，这是我的实体 bean，我希望它是唯一的，一种方法是在 Set 中获取结果列表，但由于多种原因我不喜欢这种方式:)
所以我从Child.class 而不是Parent.class 创建了一个标准，这个技巧对我有用。
Criteria c = session.createCriteria(Child.class,"c");// starting from Child
c.add(Restrictions.like("childName", "abc", MatchMode.ANYWHERE));
c.createAlias("parent", "p"); //remember parent is an attribute in Child.class
c.add(Restrictions.like("p.parentName", "xyz", MatchMode.ANYWHERE));
c.setProjection( Projections.projectionList().add(Projections.groupProperty("parent"))); //projecting parent which is an attribute of Child.class
List<Parent> result = c.list(); //get the result
for (Parent p: result) {
System.out.println(p);
}
如果您仍然不明白这里是我映射的实体 Bean 类。
package com.mazhar.beans;
import static javax.persistence.GenerationType.IDENTITY;
import java.util.List;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
@Entity
@Table(name = "parent")
public class Parent {
private Integer idParent;
private String parentName;
private List<Child> childs;
@Id
@GeneratedValue(strategy = IDENTITY)
@Column(name = "id_parent")
public Integer getIdParent() {
return idParent;
}
public void setIdParent(Integer idParent) {
this.idParent = idParent;
}
@Column(name = "parent_name")
public String getParentName() {
return parentName;
}
public void setParentName(String parentName) {
this.parentName = parentName;
}
@OneToMany(fetch=FetchType.LAZY, mappedBy="parent", cascade=CascadeType.ALL)
public List<Child> getChilds() {
return childs;
}
public void setChilds(List<Child> childs) {
this.childs = childs;
}
}
和我的孩子班
package com.mazhar.beans;
import static javax.persistence.GenerationType.IDENTITY;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
@Entity
@Table(name = "child")
public class Child {
private Integer idChild;
private String childName;
private Parent parent; //this actually we projected in criteria query.
@Id
@GeneratedValue(strategy = IDENTITY)
@Column(name = "id_city", unique = true, nullable = false)
public Integer getIdChild() {
return idChild;
}
public void setIdChild(Integer idChild) {
this.idChild = idChild;
}
@Column(name = "city_name", nullable = false)
public String getChildName() {
return childName;
}
public void setChildName(String cName) {
this.childName = cName;
}
@ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
@JoinColumn(name = "id_father")
public Parent getParent() {
return parent;
}
public void setParent(Parent parent) {
this.parent = parent;
}
}