Identifier conversion not considered during `@DocumentReference` construction

[blueiceprj]

Hi,

I use the new feature of document reference annotation @DocumentReference and have a issue about it. In case I have Country and City documents and City referenced to Country with this annotation. But "_Id" field of type on Country document is ObjectId. I write this code on City document as well:

@DocumentReference
private Country country;

When I get Country of City object it couldn't fetch data and return null. Because of Country document reference stored as String type. I think there is a type mismatch on lookup query.

I think we need like 2 options on document reference.

1. dataType parameter on DocumentReference annotation class. (example : ObjectId, String ...)
2. Or custom lookup field.

@DocumentReference(lookup = "{ '_id' : new ObjectId('?#{#target}') }")
private Country country;

or

@DocumentReference(lookup = "{ '_id' : { $oid: '?#{#target}' } }")
private Country country;

3. Spring should get the data type of referenced document and according to prepare lookup query

[blueiceprj]

I have solved this problem with converter. But I have to write converter for all referenced documents.

@WritingConverter
public class CountryDocumentPointer implements Converter<Country, DocumentPointer<ObjectId>>
{
	public DocumentPointer<ObjectId> convert(Country source) {
		return () -> new ObjectId(source.getId());                                
	}
}

[christophstrobl]

Thanks for reporting - we'll look into this.

[blueiceprj]

I have already checked again and the converter not running anyway.

[christophstrobl]

I was not able to reproduce the problem based on the given information.
The test below passes, so I might be missing something here.

static class Country {
	ObjectId id;
	String name;
}

static class City {
	String id;
	String name;

	@DocumentReference
	Country country;
}

@Test // GH-3787
void readsReferenceHaveingObjectIdTypeId() {

	Country country = new Country();
	country.name = "Austria";
	template.save(country);

	City city = new City();
	city.id = "lnz";
	city.name = "linz";
	city.country = country;
	template.save(city);

	City found = template.findOne(query(where("id").is(city.id)), City.class);
	assertThat(found.country).isEqualTo(country);
}

{
    "_id" : "lnz",
    "name" : "linz",
    "country" : ObjectId("61247fb1e3e1e638554979c8"),
    "_class" : "org.springframework.data.mongodb.core.MongoTemplateDocumentReferenceTests$City"
}

Can you provide a complete minimal sample (something that we can unzip or git clone, build, and deploy) that reproduces the problem.

[blueiceprj]

Only Country Id implementation on city and country is different. Like this :

	@MongoId(targetType = FieldType.OBJECT_ID)
	private String id;

[christophstrobl]

Thanks - yes that's the missing piece. Good catch, the field type is not considered correctly when writing the reference.

[blueiceprj]

Ok. Thank you.

[blueiceprj]

Than you for your quick response