QBC CriteriaQuery用法

Criteria查询（Criteria Query），这种查询方式把查询条件封装为一个Criteria对象。在实际应用中，使用Session的createCriteria()方法构建一个org.hibernate.Criteria实例，然后把具体的查询条件通过Criteria的add()方法加入到Criteria实例中。这样，程序员可以不使用SQL甚至HQL的情况下进行数据查询。
以下以两个实体类User、Department为例：

User:
 

import javax.validation.constraints.DecimalMax;
import javax.validation.constraints.DecimalMin;
import javax.validation.constraints.Email;
import javax.validation.constraints.Max;
import javax.validation.constraints.Min;
import javax.validation.constraints.NotEmpty;
import javax.validation.constraints.NotNull;
import javax.validation.constraints.Past;
 
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
 
 
@JsonIgnoreProperties({"dpt"})
public class User {
	private int id;
	@NotEmpty
	private String name;
	@Min(value =1) 
	@Max(value =200) 
	private int age;
	@NotEmpty
	private String pwd;
	@Past
	private Date birthday;
	@NotNull
	private Department dpt;
	@DecimalMin(value = "1")
	@DecimalMax(value = "3")
	private Double height;
	@Email
	private String email;
setter............. getter...........
}

Department:
 

import java.util.HashSet;
import java.util.Set;
 
public class Department {
	private int id;
	private String name;
	private Set users = new HashSet();
setter......  getter........
}

1. 带条件式用法：

   public List<User> selectUserold(int gt, int lt, int dep_id) {
   		//1、创建builder
   		CriteriaBuilder builder=getSession().getCriteriaBuilder();
   		//2、拿到criteriaQuery	
   		CriteriaQuery<User> criteriaQuery=builder.createQuery(User.class);
   		//3、获取到根对像，构建查询条件
   		Root<User> root=criteriaQuery.from(User.class);
   		Predicate predicate1= (Predicate) builder.gt(root.get("id"), gt);
   		Predicate predicate2= (Predicate) builder.lt(root.get("id"), lt);
   		Predicate predicate3= (Predicate) builder.equal(root.get("dpt"),dep_id);
   		Predicate predicate=builder.and(predicate1,predicate2,predicate3);
   		
   		/* 设置要获取数据的字段 */
   		criteriaQuery.select(root.get("name"));
   		
   		/* 设置条件 */
   		criteriaQuery.where(predicate);
   		
   		//4、获取query对象
   		Query<User> query=getSession().createQuery(criteriaQuery);
   		
   		//5、执行查询
   		List<User> users=query.list();
   		return users;
   	}
   

2. 获取指定字段数据：
    

	
/* CriteriaQuery根据条件查询多个字段的值 */
	public List<User> selectUser(int gt, int lt, int dep_id) {
		//1、创建builder
		CriteriaBuilder builder = getSession().getCriteriaBuilder();
		//2、拿到criteriaQuery
		CriteriaQuery<Tuple> criteria = builder.createTupleQuery();
		//3、获取到根对像，构建查询条件
		Root<User> root = criteria.from(User.class);
		
		Predicate predicate1= (Predicate) builder.gt(root.get("id"), gt);
		Predicate predicate2= (Predicate) builder.lt(root.get("id"), lt);
		Predicate predicate3= (Predicate) builder.equal(root.get("dpt"),dep_id);
		Predicate predicate=builder.and(predicate1,predicate2,predicate3);
		
		/* 设置条件 */
		criteria.where(predicate);
		
		/* 设置要获取值的字段 */
		Path<Integer> qId = root.get("id");
		Path<String> qname = root.get("name");
		
		criteria.multiselect(qId,qname);
		
		/* 获取到的结果 */
		List<Tuple> tuples = getSession().createQuery(criteria).getResultList();
		for (Tuple tuple : tuples)
		{
		   int id = tuple.get(qId);
		   String name = tuple.get(qname);
		   System.out.println(id+":"+name);
		}
		return null;
	}

需导入的包：

import javax.persistence.Tuple;
import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Join;
import javax.persistence.criteria.JoinType;
import javax.persistence.criteria.Path;
import javax.persistence.criteria.Predicate;
import javax.persistence.criteria.Root;