Spring Data MongoDB and JSR Validation using Lazy DBRef

The Problem

Recently using MongoDB and Spring Data I encountered an interesting issue. Saving an Entity  which was loaded by @DBRef(lazy = true) wasn’t possible together with the activated ValidatingMongoEventListener. Each time the following error occurred:

javax.validation.ConstraintViolationException
	at org.springframework.data.mongodb.core.mapping.event.ValidatingMongoEventListener.onBeforeSave(ValidatingMongoEventListener.java:65)
	at org.springframework.data.mongodb.core.mapping.event.AbstractMongoEventListener.onBeforeSave(AbstractMongoEventListener.java:144)
	at org.springframework.data.mongodb.core.mapping.event.AbstractMongoEventListener.onApplicationEvent(AbstractMongoEventListener.java:90)
	at org.springframework.data.mongodb.core.mapping.event.AbstractMongoEventListener.onApplicationEvent(AbstractMongoEventListener.java:33)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:163)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:136)
	at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:381)
	at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:335)
	at org.springframework.data.mongodb.core.MongoTemplate.maybeEmitEvent(MongoTemplate.java:1633)
	at org.springframework.data.mongodb.core.MongoTemplate.doSave(MongoTemplate.java:986)
	at org.springframework.data.mongodb.core.MongoTemplate.save(MongoTemplate.java:933)
	at org.springframework.data.mongodb.repository.support.SimpleMongoRepository.save(SimpleMongoRepository.java:78)

The Issue

Well, looking into the details it is quite clear — as a dynamic proxy is passed to the validation which fields are all null. As so any validation on the Entity will always fail. The code of the validator itself doesn’t really show the obvious miss take — only if you compare it with the save method the problem gets pretty clear.

ValidatingMongoEventListener

public void onBeforeSave(Object source, DBObject dbo) {

  LOG.debug("Validating object: {}", source);
  Set violations = validator.validate(source);

  if (!violations.isEmpty()) {

    LOG.info("During object: {} validation violations found: {}", source, violations);
    throw new ConstraintViolationException(violations);
  }
}

MappingMongoConverter

Compared to the Spring Mongo Mapper code, which is responsible to store the entity it’s clear what we have to do.

public void write(final Object obj, final DBObject dbo) {

  if (null == obj) {
    return;
  }

  Class<?> entityType = obj.getClass();
  boolean handledByCustomConverter = conversions.getCustomWriteTarget(entityType, DBObject.class) != null;
  TypeInformation<? extends Object> type = ClassTypeInformation.from(entityType);

  if (!handledByCustomConverter && !(dbo instanceof BasicDBList)) {
    typeMapper.writeType(type, dbo);
  }

  Object target = obj instanceof LazyLoadingProxy ? ((LazyLoadingProxy) obj).getTarget() : obj;

  writeInternal(target, dbo, type);
}

Solution

As so we have to replace the Spring provided Validation Listener with an own — till Spring fixes the issue:

public class FixedMongoValidation  extends AbstractMongoEventListener<Object> {
  private final Validator validator;
  public FixedMongoValidation(Validator validator) {
    Assert.notNull(validator);
    this.validator = validator;
  }
  @Override
  @SuppressWarnings({ "rawtypes", "unchecked" })
  public void onBeforeSave(Object obj, DBObject dbo) {

    Object target = obj instanceof LazyLoadingProxy ? ((LazyLoadingProxy) obj).getTarget() : obj;
    Set violations = validator.validate(target);

    if (!violations.isEmpty()) {

      LOG.info("During object: {} validation violations found: {}", target, violations);
      throw new ConstraintViolationException(violations);
    }
  }
}

And of course don’t forget to change the configuration to ensure your fixed class is used.

// JSR Validation for MongoDB Entities
@Bean
public ValidatingMongoEventListener validatingMongoEventListener() {
  return new ValidatingMongoEventListener(validator());
}
@Bean
public LocalValidatorFactoryBean validator() {
  return new LocalValidatorFactoryBean();
}

Links

Pull Request in Spring Data Project