为什么在尝试使用参数化的泛型获取查询时出现空列表

Question

I am trying to fetch the List of the Type as depicted in the code below -:

    @Autowired
    MongoTemplate mongotemplate;

    @Override
    public <T> List<T> getDetails(Query query, Class<T> queryClass) {

        List<T>  list= mongotemplate.find(query, queryClass);

    return list;
    }

}

This repository is called from the service as-:

return messageSummaryImpl.getDetails(query, MessageSummaryDoc.class);

and the return Type of this function is List<MessageSummaryDoc>

As the result of this is an Empty list,This code works fine when i dont use the generic function or say by directly calling the repository function from the service itself (mongorepository.find(query,Classexample.class)) Please suggest me what i am doing wrong.

PS-: please don't ask me why i am not calling the repository directly(As this is the project requirement).

Answer 1

Either you have no entires that matches query or your mongotemplate does something fancy with query.

You stated that if you do (mongorepository.find(query,Classexample.class)) you got some data, but you are not using mongorepository in given code but mongotemplate so that is "false proof of concept"

Generics won't affect this issue by any means - they are gone on runtime anyway.