ClassCastException when using PropertyValueConverter with generic types

[MrHurniak]

Dear friends, On our project we faced with issue when using PropertyValueConverter that cause ClassCastException. Here are some code snippets: Entity class with ValueConverter annotation:

@Document("user")
@Data
public class User {

    @ValueConverter(WriteInLowerCase.class)
    private String email;

}

Converter implementation:

public class WriteInLowerCase implements PropertyValueConverter<String, String, ValueConversionContext<?>> {

    @Override
    public String read(String value, ValueConversionContext<?> context) {
        return value;
    }

    @Override
    public String write(String value, ValueConversionContext<?> context) {
        return value.toLowerCase();
    }
}

And SpringData repository:

@Repository
public interface UserRepository extends MongoRepository<User, String> {

    List<AccessEntity> findAllByEmailIgnoreCase(String email);
}

After calling findAllByEmailIgnoreCase we got and exception:

java.lang.ClassCastException: class java.util.regex.Pattern cannot be cast to class java.lang.String (java.util.regex.Pattern and java.lang.String are in module java.base of loader 'bootstrap')
	at com.epam.adminpanel.repo.mongo.converter.WriteInLowerCase.write(WriteInLowerCase.java:6) ~[main/:na]
	at org.springframework.data.mongodb.core.convert.QueryMapper.getMappedValue(QueryMapper.java:440) ~[spring-data-mongodb-4.0.0.jar:4.0.0]
	at org.springframework.data.mongodb.core.convert.QueryMapper.getMappedObjectForField(QueryMapper.java:337) ~[spring-data-mongodb-4.0.0.jar:4.0.0]
	at org.springframework.data.mongodb.core.convert.QueryMapper.getMappedObject(QueryMapper.java:164) ~[spring-data-mongodb-4.0.0.jar:4.0.0]
	at org.springframework.data.mongodb.core.QueryOperations$QueryContext.getMappedQuery(QueryOperations.java:348) ~[spring-data-mongodb-4.0.0.jar:4.0.0]
	at org.springframework.data.mongodb.core.MongoTemplate.doFind(MongoTemplate.java:2463) ~[spring-data-mongodb-4.0.0.jar:4.0.0]
	at org.springframework.data.mongodb.core.ExecutableFindOperationSupport$ExecutableFindSupport.doFind(ExecutableFindOperationSupport.java:171) ~[spring-data-mongodb-4.0.0.jar:4.0.0]
	at org.springframework.data.mongodb.core.ExecutableFindOperationSupport$ExecutableFindSupport.all(ExecutableFindOperationSupport.java:134) ~[spring-data-mongodb-4.0.0.jar:4.0.0]
	at org.springframework.data.mongodb.repository.query.AbstractMongoQuery.lambda$getExecution$3(AbstractMongoQuery.java:169) ~[spring-data-mongodb-4.0.0.jar:4.0.0]
	at org.springframework.data.mongodb.repository.query.AbstractMongoQuery.doExecute(AbstractMongoQuery.java:143) ~[spring-data-mongodb-4.0.0.jar:4.0.0]
	at org.springframework.data.mongodb.repository.query.AbstractMongoQuery.execute(AbstractMongoQuery.java:118) ~[spring-data-mongodb-4.0.0.jar:4.0.0]
	at org.springframework.data.repository.core.support.RepositoryMethodInvoker.doInvoke(RepositoryMethodInvoker.java:136) ~[spring-data-commons-3.0.0.jar:3.0.0]
	at org.springframework.data.repository.core.support.RepositoryMethodInvoker.invoke(RepositoryMethodInvoker.java:120) ~[spring-data-commons-3.0.0.jar:3.0.0]
	......

The solution from our side was to update implementation of WriteInLowerCase to be without generic implementation:

public class WriteInLowerCase implements PropertyValueConverter {

    @Override
    public Object read(Object value, ValueConversionContext context) {
        return value;
    }

    @Override
    public Object write(Object value, ValueConversionContext context) {
        if (value instanceof String stringValue) {
            return stringValue.toLowerCase();
        }
        return value;
    }
}

But I believe, that types should not be ignored.

[christophstrobl]

Thanks for reporting! That's an interesting one since the PartTreeMongoQuery will create a BsonRegularExpression for IgnoreCase which then violates the PropertyValueConverter. Will take it to the team.

[mp911de]

Ideally, we fix the issue initially on the converter level by checking whether the value is assignable to the property type.

Going forward, if we capture values in other types (e.g. create a Pattern from a String), we should investigate whether we can apply conversions before the Pattern is created.

[camac]

Thanks for reporting @MrHurniak. I ran into this same problem and using the broader Object is working for now.