empty array being mapped to hashset instead of list

[albert_kam]

Using spring mongo 1.1.0 release version, and mongo-java-driver 2.9.1 here.

So, i have an arraylist that gets mapped to mongo without using any converters using the default mapper.

If the list is not empty, i can read it back with the correct type, which is java.util.ArrayList

But if if the list empty, when reading it back, it becomes a java.util.HashSet

It doesnt seem to happen in my previous version of spring mongo 1.0.4.

[Oliver Gierke]

What does your domain object look like?

[albert_kam]

Dear Oliver,

Here is a working single-java-file example that demonstrates the problem :

package kam.albert.lab.convert;

import java.util.ArrayList;
import java.util.List;

import org.bson.types.ObjectId;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Scope;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.data.mongodb.core.MongoOperations;
import org.springframework.stereotype.Component;

@Component
@Scope(value="singleton")
public class TestBug {

	@Autowired private MongoOperations ops;

	private static String collectionName = "test";

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		ApplicationContext ctx = new ClassPathXmlApplicationContext(
			"test-context.xml"
		);
		TestBug bean = ctx.getBean(TestBug.class);
		bean.test();
	}

	private void test() {
		if (!this.ops.collectionExists(collectionName)) {
			this.ops.createCollection(collectionName);
		}

		MyDomain domain = new MyDomain();

                // COMMENT THIS LINE TO MAKE THE EXCEPTION SHOWS UP
		domain.names.add("hello"); 

		this.ops.insert(domain);

		MyDomain dbDomain = this.ops.findById(domain.id, MyDomain.class);
		List<String> values = dbDomain.names.getValues();
		System.out.println("oink : " + values.getClass() + " : " + values);
	}

	private static class MyDomain {
		private ObjectId id; // just for lookup later after insertion
		private MyList<String> names;
		MyDomain() {
			this.id = new ObjectId();
			this.names = new MyList<String>();
		}
	}

	private static class MyList<T> extends MyPropertyBase<List<T>> {
		MyList() {
			this.value = new ArrayList<>();
		}
		void add(T elem) {
			this.value.add(elem);
		}
		public List<T> getValues() {
			return this.value;
		}
	}

	private static class MyPropertyBase<T> {
		T value;
	}
}

The above is a working example with the output of :

oink : class java.util.ArrayList : [hello]

One just need to comment the line :

domain.names.add("hello");

to make the exception shows up :

Exception in thread "main" java.lang.ClassCastException: java.util.HashSet cannot be cast to java.util.List
	at kam.albert.lab.convert.TestBug$MyList.getValues(TestBug.java:65)
	at kam.albert.lab.convert.TestBug.test(TestBug.java:44)
	at kam.albert.lab.convert.TestBug.main(TestBug.java:30)

Please note that this doesnt happen in 1.0.4 version.

Thank you !

[albert_kam]

Hello, it's been quite a while. Is there any followups on this ?

[Oliver Gierke]

Any chance you can incorporate this into a tiny executable test case?

[albert_kam]

Thanks for the reply.
Any pointers how should i get started ?
I am asking this because i am used to do simple tests with a running mongo instance, a custom spring xml file,
tests like the example code above, where i consider it as runnable (a void main in there) and tiny (just 1 file).

[Oliver Gierke]

You don't even need a running Mongo instance. Write the test against MappingMongoConverter.read(DBObject, Class<?>)… set up a BasicDBObject with the data as it is returned from Mongo and hand in the type you want to unmarshal the data into…

[albert_kam]

Hello again Oliver.
Okay, i am trying to do this right now.
Could you help me on how to construct a MappingMongoConverter instance ?
I still have several conversion issues, if you guide me on how to do this, i will be more than happy to give you other tests.
Thanks !

[Oliver Gierke]

Well, have a look at the JavaDoc, have a look at the already existing unit tests [0].

[0] https://github.com/SpringSource/spri...UnitTests.java