使用 Spring boot JPA 从 mysql 数据库获取 JSONArray

如何解决使用 Spring boot JPA 从 mysql 数据库获取 JSONArray

在我的 MysqL 表中有列存储 'JSONArray'

这是 spring-boot 项目中模型类的一部分。

UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'findindex' of undefined
    at User.addToCart (D:\Pradip_All\Nodejs- tutorials video (MONGODB)\models\user.js:20:46)
    at D:\Pradip_All\Nodejs- tutorials video (MONGODB)\controllers\shop.js:70:23
    at processticksAndRejections (internal/process/task_queues.js:93:5)
(Use `node --trace-warnings ...` to show where the warning was created)
(node:11212) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block,or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection,use the CLI flag `--unhandled-rejections=strict` 
(see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
(node:11212) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future,promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

已经是具有空构造函数、具有所有字段、getter 和 setter 的构造函数的模型类。

这是我的 SubQuestionsRepository 接口。

public class SubQuestions implements Serializable{
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "sub_questionId",nullable = false,columnDeFinition = "INT(11) UNSIGNED")
    private Integer sub_questionId;

    private JSONArray answers;

}

这是我的控制器类的一部分。

public interface SubQuestionsRepository extends Serializable,JpaRepository<Questions,Integer>{

}

但是当我调用“getallnestedques()”方法时，它给出了以下错误。

public class SubQuestionsController implements Serializable{
 private SubQuestionsRepository subquestionsrepository;


    public SubQuestionsController(SubQuestionsRepository subquestionsrepository) {
        super();
        this.SubQuestionsRepository = subquestionsrepository;
    }

    @GetMapping("/getall")
    public  Collection<SubQuestions> getallnestedques(){
        return subquestionsrepository.getactiveques();
    }
}

我如何解决这个问题？

解决方法

您可以尝试以下解决方案吗？

需要将 answers 列声明为 Lob，如下例所示：

import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Convert;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Lob;

import org.json.JSONArray;

@Entity
public class SubQuestions implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "sub_questionId",nullable = false,columnDefinition = "INT(11) UNSIGNED")
    private Integer sub_questionId;

    @Lob
    @Column
    @Convert(converter = JSONArrayConverter.class)
    private JSONArray answers;
}

属性转换器JSONArrayConverter在存储到数据库之前将JSONArray对象转换为String，并在从数据库读取值后转换为JSONArray：

import javax.persistence.AttributeConverter;
import javax.persistence.Converter;

import org.json.JSONArray;
import org.slf4j.LoggerFactory;

import ch.qos.logback.classic.Logger;

@Converter(autoApply = true)
public class JSONArrayConverter implements AttributeConverter<JSONArray,String> {

    private static final Logger logger = (Logger) LoggerFactory.getLogger(JSONArrayConverter.class);

    @Override
    public String convertToDatabaseColumn(JSONArray array)
    {
        String data = null;
        try
        {
            data = array.toString();
        }
        catch (final Exception e)
        {
            logger.error("JSON writing error",e);
        }

        return data;
    }

    @Override
    public JSONArray convertToEntityAttribute(String data)
    {
        JSONArray array = null;

        try
        {
            array = new JSONArray(data);
        }
        catch (final Exception e)
        {
            logger.error("JSON reading error",e);
        }

        return array;
    }
}