mybatis写查询条件,or查询,清空查询条件等

一时失言乱红尘 2022-05-13 11:34 732阅读 0赞

最近在项目上遇到了点关于mybatis的查询问题.  
常见的mybatis查询方式是:  
ServiceExample.Criteria srCriteria = serviceExample.createCriteria();

ServiceExample serviceExample = new ServiceExample();
                ServiceExample.Criteria srCriteria = serviceExample.createCriteria();
                srCriteria.andProjectEqualTo(project.getId());
                srCriteria.andTypeEqualTo(1);
                Service service = questionService.getService(serviceExample);

或者  
ServiceExample.Criteria srCriteria = serviceExample.or();

那么,这两者有什么区别,改什么时候用哪个呢.

查看源码:  
createCriteria()方法,只是在第一次建的时候,会把criteria放到oredCriteria中,其他时候,则不会;  
(所以要小心.切记只有确认是第一次或者之前的已经被清空了,才能用createCriteria()方法.  
不然就需要手动调用example.or(criteria)或者example.and(criteria)，把后续新建的criteria加入  
oredCriteria列表中，不然后面的criteria均不会作为查询条件  
)

而or()方法,则是每次都会把新建的Criteria 放入oredCriteria中,即:类似于or查询条件.多个联合.

public Criteria createCriteria() {
            Criteria criteria = createCriteriaInternal();
            if (oredCriteria.size() == 0) {
                oredCriteria.add(criteria);
            }
            return criteria;
        }
        
    public Criteria createCriteria() {
            Criteria criteria = createCriteriaInternal();
            if (oredCriteria.size() == 0) {
                oredCriteria.add(criteria);
            }
            return criteria;
        }
    
        protected Criteria createCriteriaInternal() {
            Criteria criteria = new Criteria();
            return criteria;
        }
        
    	public Criteria or() {
            Criteria criteria = createCriteriaInternal();
            oredCriteria.add(criteria);
            return criteria;
        }

清空查询条件

xxxExampler.clear();  
public void clear() \{  
oredCriteria.clear();  
orderByClause = null;  
distinct = false;  
\}

yuanma

public class ServiceExample extends AbstractPojo {
        /**
         * This field was generated by MyBatis Generator.
         * This field corresponds to the database table service
         *
         * @mbggenerated
         */
        protected String orderByClause;
    
        /**
         * This field was generated by MyBatis Generator.
         * This field corresponds to the database table service
         *
         * @mbggenerated
         */
        protected boolean distinct;
    
        /**
         * This field was generated by MyBatis Generator.
         * This field corresponds to the database table service
         *
         * @mbggenerated
         */
        protected List<Criteria> oredCriteria;
    
        /**
         * This method was generated by MyBatis Generator.
         * This method corresponds to the database table service
         *
         * @mbggenerated
         */
        public void clear() {
            oredCriteria.clear();
            orderByClause = null;
            distinct = false;
        }
    }

测试条件

//测试
            ProductExample productExample = new ProductExample();
            ProductExample.Criteria productCriteria = productExample.createCriteria();
            productCriteria.andIdEqualTo(5L);
            
            ProductExample.Criteria productCriteria4 = productExample.createCriteria();
            productCriteria4.andIdEqualTo(6L);
            //查出来的还是id是5的,因为第二次调用ProductExample.Criteria productCriteria4 = productExample.createCriteria();
            //所产生的Criteria并未放入productExample的List<Criteria> oredCriteria中.用or方法产生的才会放入
            List<Product> products = sqlSession.selectList("ProductMapper.selectByExample", productExample);
            //能查出一个
            System.out.println("product1:" + products.toString());
            
            //能查出两个.or条件的作用.
            ProductExample.Criteria productCriteriaOr = productExample.or();
            productCriteriaOr.andIdEqualTo(6L);
            List<Product> products2 = sqlSession.selectList("ProductMapper.selectByExample", productExample);
            System.out.println("product2:" + products2.toString());
            
            //调用清空方法,清空之前的查询条件
            productExample.clear();
            //清空之后,需要重新生成查询条件Criteria
            productCriteria = productExample.createCriteria();
            //不设置条件,相当于不需要条件,全部查出了
            //productCriteria.andIdEqualTo(5L);
            List<Product> products3 = sqlSession.selectList("ProductMapper.selectByExample", productExample);
            System.out.println("product3:" + products3.toString());