skip query returns the same Snapshot with MongoDB

[antongub]

Clear description of my expectations versus reality
When I use the QueryBuilder skip method with two consecutive parameters (e.g. first with '1' and then with '2'), I expect to get different results each time I execute the query in my Javers find method, but this is not happening.

Steps To Reproduce
I have a **runnable test case ** which isolates the bug and allows Javers Core Team to easily reproduce it. I have pushed this test case to my fork of this repository:

https://github.com/antongub/javers/blob/master/javers-persistence-mongo/src/test/groovy/org/javers/repository/mongo/cases/SkipQueryTest.groovy

import com.mongodb.client.MongoDatabase
import org.javers.core.JaversBuilder
import org.javers.core.metamodel.annotation.Entity
import org.javers.core.metamodel.annotation.Id
import org.javers.core.metamodel.annotation.ValueObject
import org.javers.repository.jql.QueryBuilder
import org.javers.repository.mongo.BaseMongoTest
import org.javers.repository.mongo.MongoRepository


class SkipQueryTest extends BaseMongoTest {

    @Entity
    class Customer {
        @Id
        String id

        Configuration conf = new Configuration()

        Customer(id) {
            this.id = id
        }
    }

    @ValueObject
    class Configuration {
        String currency = "EUR"
    }


    def "should return two different snapshot ids"() {
        given:
        Customer customer1 = new Customer("1")
        Customer customer2 = new Customer("2")

        MongoDatabase mongo = mongoClient.getDatabase("test")
        def repo = new MongoRepository(mongo)
        def javers = JaversBuilder.javers().registerJaversRepository(repo).build()

        when:
        javers.commit("author", customer1)
        javers.commit("author", customer2)

        then:
        def query1 = QueryBuilder.anyDomainObject().limit(1).skip(0).build()
        def query2 = QueryBuilder.anyDomainObject().limit(1).skip(1).build()
        def snapshot1Id = javers.findSnapshots(query1)[0].globalId
        def snapshot2Id = javers.findSnapshots(query2)[0].globalId
        snapshot1Id != snapshot2Id
    }
}

result:

Condition not satisfied:

snapshot1Id != snapshot2Id
|           |  |
|           |  ...SkipQueryTest$Customer/2#conf
|           false
...SkipQueryTest$Customer/2#conf

Condition not satisfied:

snapshot1Id != snapshot2Id
|           |  |
|           |  ...SkipQueryTest$Customer/2#conf
|           false
...SkipQueryTest$Customer/2#conf

	at org.javers.repository.mongo.cases.SkipQueryTest.should return two different snapshot ids(SkipQueryTest.groovy:55)

Javers' Version
7.4.5

Additional context
The issue only occurs when an entity contains at least one ValueObject. This is because the entity along with its ValueObjects all share the same commit_id and the snapshots are only sorted by the commit_id (or commit_date_instant if instructed). Therefore, the fix involves adding an additional sorting criterion that differentiates each entry else MongoDB's natural (default) ordering takes effect.

[antongub]

I've created a simple solution in this Pull Request: #1392

[bartoszwalacik]

I like it, thanks @antongub for this neat fix. I changed it a bit to keep the right order of col names in the sort clause

[bartoszwalacik]

This fix will be released in 7.5.0