Spring Boot MongoDB - MongoDB cannot generate 'ID' - spring

Question

I have some problem with my Spring Boot application.
When I save one document in my repository application works fine, but when I save more than one documents, my aplication not working. Here is my code.
Article.java
import org.springframework.data.annotation.Id;
public class Article {
#Id
private String id;
private String title;
private String description;
public Article() {}
public Article(String title, String description) {
this.title = title;
this.description = description;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
#Override
public String toString() {
return "Article{" +
"id='" + id + '\'' +
", title='" + title + '\'' +
", description='" + description + '\'' +
'}';
}
}
ArticleRepository.java
public interface ArticleRepository extends MongoRepository<Article, String> {}
DatabaseLoader.java
import java.util.HashSet;
import java.util.Set;
#Component
public class DatabaseLoader implements CommandLineRunner {
#Autowired
private ArticleRepository articleRepository;
#Override
public void run(String... args) throws Exception {
articleRepository.deleteAll();
// example 1: if I save one document to my repo everything works fine
// example: articleRepository.save(new Article("Title 1", "description 1"));
// console returns: Article{id='596f480e4e118123574a13f1', title='Title 1', description='description 1'}
// but here is problem
Set<Article> articleList = new HashSet<Article>(){
{
add(new Article("Title 1", "description 1"));
add(new Article("Title 2", "description 2"));
}
};
// because if I try to save my collection
articleRepository.save(articleList);
// console returns: com.mongodb.DuplicateKeyException:
// Write failed with error code 11000 and error message
// 'insertDocument :: caused by :: 11000 E11000 duplicate key
// error index: test.article.$user dup key: { : null }'
System.out.println(articleRepository.findAll());
}
}
Application.java
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
#SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication.run(SimpleMongoApplication.class, args);
}
}
Do you know, why I have this problem?
Thank you for all your answers.

Answer 1

OK, here is #Afridi's solution.
All you need to do is adding #Document(collection="collection-name") annotation in your document. here is an example:
#Document(collection = "articles") // here is solution
public class Article {
#Id
private String id;
private String title;
private String description;
//getters, setters and constructor
}