ConversionFailedException:保留DBObject但检索返回LinkedHashMap <?,?&gt;. [英] ConversionFailedException: Persisting a DBObject but retrieving returns a LinkedHashMap&lt;?, ?&gt;

问题描述

我要保留一个对象:

@Document
public class PotentialCandidates {

    @Id
    private String jobid;

    @CreatedDate
    private DateTime created;

    @LastModifiedDate
    private DateTime modified;

    private DBObject potentialcandidates;

    public String getJobid() {
        return this.jobid;
    }   
    public void setJobid(String jobid) {
        this.jobid = jobid;
    }

    public DBObject getPotentialcandidates() {
        return this.potentialcandidates;
    }   
    public void setPotentialcandidates(DBObject potentialcandidates) {
        this.potentialcandidates = potentialcandidates;
    }

}

其中potentialCandidates是通过JSON字符串设置的，如下所示:

where potentialCandidates are set from a JSON string as so:

potentialCandidatesObj.setPotentialcandidates((DBObject)JSON.parse(valStr));

这对于我的mongodb仍然有效，并在我可以深入到的DB上给了我一个对象，但是当我尝试检索我的db对象时:

This persists fine to my mongodb and gives me an object on the DB I can drill down into, however when I try to retrieve my db object:

    public PotentialCandidates getPotentialCandidatesByJobid(String jobid) throws NoSuchPotentialCandidatesException , SystemException{

    PotentialCandidates Jobid = null;
try {
            Query query = new Query();
            query.addCriteria(Criteria.where("_id").is(jobid));
            Jobid = mongoTemplateJobs.findOne(query, PotentialCandidates.class,
                    COLLECTION_NAME);

            return Jobid;
        } catch (Exception ex) {
            throw new SystemException(ex);
        } finally {
            if (Jobid == null) {
                throw new NoSuchPotentialCandidatesException("No User with jobid: "
                        + jobid + "found..");
            }
        }
}

我遇到以下错误:

org.springframework.core.convert.ConversionFailedException: Failed to convert from type java.util.ArrayList<?> to type com.mongodb.DBObject for value 'myString'; nested exception is org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from type java.util.LinkedHashMap<?, ?> to type com.mongodb.DBObject

因此，似乎我需要某种逻辑来处理从mongo进行的检索.我可以在findOne查询中使用其他返回类，但这似乎有些混乱.有标准的处理方法吗?

So it would seem I need some sort of logic to handle retrieves from mongo. I could use a different return class in my findOne query but that seems a little messy. Is there a standard approach to dealing with this?

推荐答案

您的错误可能恰恰是您在例外情况中所说的:ConversionFailed Exception是由某人/某人试图将ArrayList转换为LinkedHashMap引起的;但是没有适合的转换器(ConverterNotFoundException).

your error is probably exactly what it says in your exception: a ConversionFailed Exception caused by someone/something trying to convert from ArrayList to a LinkedHashMap; but there is just no fitting converter for that (ConverterNotFoundException).

确切地说这是发生在哪里，因为您只发布了很少的代码.我在您的代码中找不到字符串"myString"，但在错误中提到了它.

where exactly this is happening is impossible to say since you only posted very little code. i can not find the String "myString" in your code, yet it is mentioned in the error.

有没有标准的方法来处理这个问题?

Is there a standard approach to dealing with this?

spring数据通常在其映射过程中使用转换器.为了更好地控制映射过程，有些人更喜欢为其类实现和注册自定义转换器.

spring data usually uses converters in its mapping process. to have more control over the mapping process some people prefer to implement and register a custom converter for their classes.

您可以在此处了解有关转换器的信息

you can read about converters here

http://docs.spring.io/spring-data/data-mongo/docs/current/reference/html/mongo.core.html#mongo.custom-converters

在这里

http://docs.spring.io /spring/docs/current/spring-framework-reference/html/validation.html#core-convert

也许这已经足够您自己修复错误.

maybe this will already be enough for you to fix the error yourself.

关于此行的简短评论:

potentialCandidatesObj.setPotentialcandidates((DBObject)JSON.parse(valStr));

您将在调用setter之前强制转换为DBObject，因为setter需要一个DBObject.这很不好，您应该为JSON创建另一个setter并在那里进行转换，否则最终将在代码中的任何地方执行该转换操作；那不是很干.

you are casting to DBObject before calling the setter, because the setter takes a DBObject. this is bad, you should create another setter for JSON and do the casting there, or you will end up doing that casting operation everywhere in your code; that's not very DRY.

spring数据中还有一个叫做DBRefs的东西: The mapping framework doesn't have to store child objects embedded within the document. You can also store them separately and use a DBRef to refer to that document. When the object is loaded from MongoDB, those references will be eagerly resolved and you will get back a mapped object that looks the same as if it had been stored embedded within your master document. 您可能更喜欢嵌入式DBObject.

there is also something called DBRefs in spring data: The mapping framework doesn't have to store child objects embedded within the document. You can also store them separately and use a DBRef to refer to that document. When the object is loaded from MongoDB, those references will be eagerly resolved and you will get back a mapped object that looks the same as if it had been stored embedded within your master document. you might prefer this over a embedded DBObject.

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