How can we create Auto generated field for mongodb using spring boot

Question

I write some code.I want to make questionId field in BaseQuestion Class as Autogenerated.Any solution for that? I am not using jpa jar.so i can\'t use @G

Answer 1

MongoDB came with all sophisticated ObjectId generation feature, but often you just jumped the ship from relational database, and you still want an easy to read / communicate numeric identifier field which automatically increments every time new record is inserted.

One neat suggestion from MongoDB tutorial is to use a counter collection with a ‘counter name’ as its id, and a ‘seq’ field to store the last used number.

When developing using Spring Data MongoDB, this neat trick can be written as a simple service. Here I used the collection name as the counter name so it’s easy to guess / remember.

import static org.springframework.data.mongodb.core.FindAndModifyOptions.options;
import static org.springframework.data.mongodb.core.query.Criteria.where;
import static org.springframework.data.mongodb.core.query.Query.query;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.mongodb.core.MongoOperations;
import org.springframework.data.mongodb.core.query.Update;
import org.springframework.stereotype.Service;

import com.model.CustomSequences;


@Service
public class NextSequenceService {
    @Autowired private MongoOperations mongo;

    public int getNextSequence(String seqName)
    {
        CustomSequences counter = mongo.findAndModify(
            query(where("_id").is(seqName)),
            new Update().inc("seq",1),
            options().returnNew(true).upsert(true),
            CustomSequences.class);
        return counter.getSeq();
    }
}

CustomSequences is just a simple class representing the collection. Please beware the usage of int data type, this will limit to 2^31 entries maximum.

import org.springframework.data.annotation.Id;
import org.springframework.data.mongodb.core.mapping.Document;

@Document(collection = "customSequences")
public class CustomSequences {
    @Id
    private String id;
    private int seq;

// getters and setters
}

Then when inserting a new entry (with help of Spring MongoDB Repository support), just set the id field like this before you save it

BaseQuestion baseQuestion = new BaseQuestion();
baseQuestion.setQuestionId(nextSequenceService.getNextSequence("customSequences"));
/* Rest all values */

baseQuestionRepository.save(baseQuestion);

If you don't like this way then you need to use MongoDBEvents and use onBeforeConvert to generate automated value using same above approach.

Also above approach is threadsafe as findAndModify() is a thread safe atomic method