Add APIs to inform components of stale objects in DataProvider (#8271)

* Add DataProvider refreshItem for single item update

* Add 'id' concept for DataProviders

This patch also adds a simplified data provider that can replace items
based on their id. This can be used to simulate stale objects from an actual
backend.

* Add refresh logic to Grid SelectionModels

* Remove broken equals and hashCode

* Refresh KeyMapper, clean up some methods

* Fix UI.access in test

* Fix tests and Grid single selection model

* Do clean up before replacing data provider

* Check correct variable for null value

* Fix other selects, add generic tests

* Code style fixes, removed assert

* Merge remote-tracking branch 'origin/master' into 286_refresh_items

* Fix documentation for refreshing an item

* Improve introduction chapter, minor clarifications

* Merge remote-tracking branch 'origin/master' into 287_refresh_items

* Add missing parameters in unit tests

1 files changed, 46 insertions, 1 deletions

diff --git a/documentation/datamodel/datamodel-providers.asciidoc b/documentation/datamodel/datamodel-providers.asciidoc
index 6b5fea2275..80b9fb9cb4 100644
--- a/documentation/datamodel/datamodel-providers.asciidoc
+++ b/documentation/datamodel/datamodel-providers.asciidoc
@@ -181,7 +181,7 @@ Button modifyPersonButton = new Button("Modify person",
 
     personToChange.setName("Changed person");
 
-    dataProvider.refreshAll();
+    dataProvider.refreshItem(personToChange);
 });
 ----
 
@@ -572,3 +572,48 @@ public class PersonDataProvider
   }
 }
 ----
+
+[[lazy-refresh]]
+=== Refreshing
+
+When your application makes changes to the data that is in your backend, you might need to make sure all parts of the application are aware of these changes.
+All data providers have the `refreshAll`and `refreshItem` methods. 
+These methods can be used when data in the backend has been updated.
+
+For example Spring Data gives you new instances with every request, and making changes to the repository will make old instances of the same object "stale".
+In these cases you should inform any interested component by calling `dataProvider.refreshItem(newInstance)`. 
+This can work out of the box, if your beans have equals and hashCode implementations that check if the objects represent the same data.
+Since that is not always the case, the user of a `CallbackDataProvider` can give it a `ValueProvider` that will provide a stable ID for the data objects. 
+This is usually a method reference, eg. `Person::getId`.
+
+As an example, our service interface has an update method that returns a new instance of the item. 
+Other functionality has been omitted to keep focus on the updating.
+
+[source, java]
+----
+public interface PersonService {
+  Person save(Person person);
+}
+----
+
+Part of the application code wants to update a persons name and save it to the backend.
+
+[source, java]
+----
+PersonService service;
+DataProvider<Person, String> allPersonsWithId = new CallbackDataProvider<>(
+  fetchCallback, sizeCallback, Person::getId);
+
+NativeSelect<Person> persons = new NativeSelect<>();
+persons.setDataProvider(allPersonsWithId);
+
+Button modifyPersonButton = new Button("Modify person",
+  clickEvent -> {
+    Person personToChange = persons.getValue();
+
+    personToChange.setName("Changed person");
+
+    Person newInstance = service.save(personToChange);
+    dataProvider.refreshItem(newInstance);
+});
+----