spring data mongodb: access default POJO converter from within custom converter

Question

I have spring data mongo custom converters setup via xml as follows

<mongo:mapping-converter id="mongoConverter" db-factory-ref="mongoDbFactory">
    <mongo:custom-converters>
        <mongo:converter ref="customWriteConverter" />
        <mongo:converter ref="customReadConverter" />
    </mongo:custom-converters>
</mongo:mapping-converter>

<bean id="mongoTemplate" class="org.springframework.data.mongodb.core.MongoTemplate">
    <constructor-arg ref="mongoDbFactory"/>
    <constructor-arg ref="mongoConverter"/>
</bean>

<bean id="customWriteConverter" class="package.WriteConverter" />
<bean id="customReadConverter" class="package.ReadConverter" />

In the custom read/write converter, I would like to re-use spring-data-mongo's default pojo converter to save certain properties as subdocuments.

consider a simplified example -

class A {
    B b;
    String var1;
    int var2;
}

class B {
    String var3;
    String var4;
}

I want to handle conversion of class A using customWriteConverter and customReadConverter, but in my custom converters I also want to delegate conversion of class B back to spring-data-mongo's default POJO converter.

How can I do this? I have not been able to successfully autowire a MongoConverter or MongoTemplate into the custom converter since the MongoConverter/MongoTemplate bean creation is in progress when it tries to create the custom converter. Is it possible to get access to the default converter and use that from within the custom converter?

Answer 1

This method is used in MongoTemplate class to get a default converter.

private static final MongoConverter getDefaultMongoConverter(MongoDbFactory factory) {
    DbRefResolver dbRefResolver = new DefaultDbRefResolver(factory);
    MappingMongoConverter converter = new MappingMongoConverter(dbRefResolver, new MongoMappingContext());
    converter.afterPropertiesSet();
    return converter;
}

MappingMongoConverter is not final and so can be overridden for a specific purpose. As mentioned in my comment above, look at this question to maybe find out solution to your problem.

Answer 2

If you are converting TO mongo database and want to default some conversions, you could do something like this:

    ...

    @Resource
    private ObjectFactory<MappingMongoConverter>
        mappingMongoConverterObjectFactory;

    private MappingMongoConverter
        mappingMongoConverter;

    ...

    //Otherwise, use default MappingMongoConverter
    //
    if (result == null)
        result =
            getMappingMongoConverter()
                .convertToMongoType(
                    value
                );

    ...

    MappingMongoConverter getMappingMongoConverter() {
        if (mappingMongoConverter == null)
            mappingMongoConverter =
                mappingMongoConverterObjectFactory.getObject();
        return
            mappingMongoConverter;
    }

The MappingMongoConverter cannot be directly @Resource (ed) in my case since it's in the process of being constructed when other converters are being built. So, Spring detects a circular reference. I am not sure if there is a better "lazy" method of doing this without all the run-around of ObjectFactory, getter method, and caching.

Now, if someone can figure out a method of defaulting to standard processing while going back (from DBObject to java Object) that would complete this circle.