Dependent fields
Options that depend on another field, like cities of the selected country
DependsOn makes a field's options depend on another field on the same form. The classic case: pick a country, then a city in that country.
using StellarAdmin.EntityFrameworkCore;
fields.Add(destination => destination.CountryId).UseSelectEditor(select =>
select.UseItems<Country>(country => country.Id, country => country.Name));
fields.Add(destination => destination.CityId)
.DependsOn(destination => destination.CountryId)
.UseSelectEditor(select =>
select.UseItems<City>(
city => city.Id,
city => city.Name,
items => items.Where<Destination>((city, destination) => city.CountryId == destination.CountryId)));When the country changes, the city field reloads its options and clears its value. While no country is picked, the city field is disabled and says "Select Country first".
It works with every choice editor and both lookups, on create and edit pages, create sheets and inline rows. Dependencies can chain: country, then city, then neighbourhood.
Changing the empty text
.DependsOn(destination => destination.CountryId,
country => country.EmptyText = "Pick a country to see its cities")When the options come from a resource
If the related type is a resource, filter it with UseResource. The editor already knows the form's type:
fields.Add(destination => destination.CityId)
.DependsOn(destination => destination.CountryId)
.UseSelectEditor(select => select.UseResource<City>(items =>
items.Where((city, destination) => city.CountryId == destination.CountryId)));This needs an EF Core resource. A resource with a custom data source can't apply the filter, so it's ignored and reported as a configuration problem.
Without EF Core
Choice editors can load their options with a function that gets the form:
fields.Add(destination => destination.CityId)
.DependsOn(destination => destination.CountryId)
.UseSelectEditor(select => select.UseItems((destination, services, cancellationToken) =>
services.GetRequiredService<CityDirectory>()
.ListAsync(destination.CountryId, cancellationToken)));For a lookup, derive the source from LookupSource<TItem, TValue, TArgument>. Its SearchAsync gets an argument that the field takes from the form:
fields.Add(guide => guide.HomeBase)
.DependsOn(guide => guide.CountryId)
.UseLookupSheetEditor(lookup => lookup.UseSource<CountryAirportSource>(guide => guide.CountryId));public class CountryAirportSource(AirportClient client) : LookupSource<Airport, string, int>
{
public override string GetValue(Airport airport) => airport.Code;
public override string GetTitle(Airport airport) => airport.City;
public override Task<IReadOnlyCollection<Airport>> FindAsync(
IReadOnlyCollection<string> values, CancellationToken cancellationToken) =>
client.FindAsync(values, cancellationToken);
public override Task<LookupPage<Airport>> SearchAsync(
int countryId, LookupQuery query, CancellationToken cancellationToken) =>
client.SearchAsync(countryId, query.Term, query.Skip, query.Take, cancellationToken);
}If the search needs several values, pass a record of them as the argument.
Things to know
- The form your filter gets only has the fields named in
DependsOnfilled in, plus the key on an edit page. If your filter reads another field, add aDependsOnfor it too. - Saving doesn't check that the city belongs to the country. Validate that yourself if it matters, in a handler or with
IValidatableObject. - Fields can't be made read-only or disabled live as other fields change.
DependsOnonly changes options.