Spring Boot 学习研究笔记(十) -SpringBoot JAP 踩坑总结

SpringBoot JAP 踩坑总结

一、 JSON 字段映射处理流程

1、实现类型转换接口

package com.call.show.common.utils;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import javax.persistence.AttributeConverter;
import javax.persistence.Converter;
import java.io.IOException;
import java.io.Serializable;
@Converter(autoApply = true)
public class JsonConverter implements AttributeConverter<Object,String>,Serializable {
    private final static ObjectMapper objectMapper = new ObjectMapper();
    @Override
    public String convertToDatabaseColumn(Object meta) {
        try {
            return objectMapper.writeValueAsString(meta);
        } catch (JsonProcessingException ex) {
            return null;
        }
    }
    @Override
    public Object convertToEntityAttribute(String dbData) {
        try {
            return objectMapper.readValue(dbData, Object.class);
        } catch (IOException ex) {
            return null;
        }
    }
}

2、实体类中添加注解

@Convert(converter=JsonConverter.class)

例如：

/**
     * 账号信息 备用字段
     */
    @Column(name = "account_info")
    @Convert(converter=JsonConverter.class)
    private  String  accountInfo ;
    /**
     * 扩展信息备用字段
     */
    @Column(name = "extended_info")
    @Convert(converter=JsonConverter.class)
    private  String  extendedInfo ;

二、JPA中的jpql-@Query的查询使用

1、单参数查询

@Query(value="select * from cst_customer where cust_name=?1",nativeQuery = true)

@Query(value="from Customer  where cust_name= ?1")

@Query(value="select c from Customer  c where c.custName=?1")

@Query(value="from Customer c where c.custName=:#{#custName}")

@Query(value="from Customer c where c.custName=:custName") List<Customer> findAllCustomerByName(@Param("custName") String custName);

123456

这几种方式是等价的

• @Query(value=“select * from cst_customer where cust_name= ?1”,nativeQuery = true)
  
• @Query(value=“from Customer where cust_name= ?1”)
  
• @Query(value=“select c from Customer c where c.custName=?1”)
  
• @Query(value=“from Customer c where c.custName=:#{#custName}”)
  
• @Query(value=“from Customer c where c.custName=:custName”)
  

2、多参数查询

@Query(value="from Customer  c where c.custId=?2 and c.custName=?1")

@Query(value="from Customer  c where c.custId=:#{#custId} and c.custName=:#{#custName}")

@Query(value="from Customer  c where c.custId=:custId and c.custName=:custName")

List<Customer> findCustomersByNameAndIndus(@Param("custName") String name,@Param("custId") Long id);

1234

这几种方式是等价的

• @Query(value=“from Customer c where c.custId=?2 and c.custName=?1”)
  
• @Query(value=“from Customer c where c.custId=:#{#custId} and c.custName=:#{#custName}”)
  
• @Query(value=“from Customer c where c.custId=:custId and c.custName=:custName”)
  

3.传对象

这里需要特别注意，可能很多人会写错

传对象的语法是： :#{#对象名称.对象属性} 如下图

@Query(value="from Customer  c where c.custId=:#{#customer.custId}")

Customer findCustomerByInfo(@Param("customer") Customer customer);

三、自定义的@Query报异常

org.springframework.dao.InvalidDataAccessApiUsageException: For queries with named parameters you need to use provide names for method parameters. Use @Param for query method parameters, or when on Java 8+ use the javac flag -parameters

通过@Query注解返回视图对象列表 ：

public interface StudentRepository extends CrudRepository<Student, Integer> {
  @Query(
      "select new com.alphathur.jpademo.model.vo.StudentVo(name, age) from Student where salary = :salary ")
  List<StudentVo> findStudentVo(Double salary);
}

这个接口使用了‘ :参数名’ 来绑定参数，且没有对salary使用@Param参数，所以报错了。

解决问题方案：

加上@Param，将接口修改如下：

public interface StudentRepository extends CrudRepository<Student, Integer> {
  @Query(
      "select new com.alphathur.jpademo.model.vo.StudentVo(name, age) from Student where salary = :salary ")
  List<StudentVo> findStudentVo(@Param("salary") Double salary);