ComboBox and original value as an array - vaadin

Question

I have a legacy MongoDB database (collection) where there is single value stored as an array List . But its only a one value that must be, in UI selected with ComboBox. So I have a model bean
class Project {
List<Company> companies;
}
And I would like to bind it and edit with VAADIN ComboBox. Initialy I thought I can use some customer converter for ComboBox but can't get it to work. Combo should edit the first value in the List (Company bean) and store back into companies field as an array to remain compatible. Is it event possible to do it and if so can you give me some hint how to accomplish this?
EDIT: Enhanced explanation
MongoDB model:
class Project {
List<Company> companies;
}
Vaadin UI:
ComboBox companies;
... 'companies' ComboBox is attached to BeanItemContainer which is List ... selection is therefore the only one Company bean, but should be stored, for compatibility reasons, as List with only one item. So basicly ComboBox should be able to read existing List value as single Company, allow selection and store it as List with this one selecten Company.

Answer 1

After the last question update the answer below may not be correct. Waiting for OP to provide details so the answer can be corrected.
You can use a sort of a delegation approach using a ProjectDelegator wrapper. This will allow you to bind the form to the Project name (using the project field) as well as the Company name (using the getCompany() getter)
1. The UI class
#PreserveOnRefresh
#SpringUI
public class MyVaadinUI extends UI {
#Override
protected void init(VaadinRequest request) {
final VerticalLayout layout = new VerticalLayout();
layout.setMargin(true);
setContent(layout);
// add the form to the UI
layout.addComponent(new MyForm(new ProjectDelegator(new Project("myProject", new Company("myCompany")))));
}
}
2. The form
// "wrapping" the form in a custom component. not really needed but a nice touch
public class MyForm extends CustomComponent {
public MyForm(ProjectDelegator projectDelegator) {
FormLayout layout = new FormLayout();
// use a binder to create fields and bind the members using reflection
BeanFieldGroup<ProjectDelegator> binder = new BeanFieldGroup<>(ProjectDelegator.class);
// bind the project name using the "project" field
layout.addComponent(binder.buildAndBind("Project", "project.name"));
// bind the company name using the "getCompany" method
layout.addComponent(binder.buildAndBind("Company", "company.name"));
// add a "save" button
layout.addComponent(new Button("Save", new Button.ClickListener() {
#Override
public void buttonClick(Button.ClickEvent clickEvent) {
try {
// commit changes
binder.commit();
} catch (FieldGroup.CommitException e) {
// didn't expect this! what gives?!
System.out.println("Could not save data: [" + e.getMessage() + "]");
}
}
}));
// set the delegator as the binder data source
binder.setItemDataSource(projectDelegator);
setCompositionRoot(layout);
}
}
3. The "delegator"
// delegator class to adapt from/to list with only 1 item
public class ProjectDelegator {
// nice constant to express the intent as clearly as possible
private static final int MY_ONLY_COMPANY = 0;
// our delegate
private Project project;
public ProjectDelegator(Project project) {
this.project = project;
}
// BeanFieldGroup will use this by reflection to bind the "company.name" field
public Company getCompany() {
// delegate the accessing to the origina product
return project.getCompanies().get(MY_ONLY_COMPANY);
}
// accessor; can if not required at a later time
public Project getProject() {
return project;
}
}
4. The legacy model classes
// our problem class
public class Project {
private String name;
private List<Company> companies = new ArrayList<>();
public Project(String name, Company company) {
this.name = name;
companies.add(company);
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public List<Company> getCompanies() {
return companies;
}
public void setCompanies(List<Company> companies) {
this.companies = companies;
}
}
// the "indirect" problem :)
public class Company {
private String name;
public Company(String name) {
this.name = name;
}
public String getName() {
return name;
}
public void setName(String name) {
System.out.println("Setting actual company name to [" + name + "]");
this.name = name;
}
}
5. Resulting UI
6. Pressing the save button
Setting actual company name to [myNewCompany]