README.md

GroupedRealmCollection

A set of extension methods that can project Realm Xamarin collections to data bindable grouped collections that can be passed directly to a Xamarin.Forms ListView.

Getting started

Just add the Realm.GroupedCollection package to your project.

Sample usage

// In your ViewModel
Students = realm.All<School>().ToGroupedCollection(school => school.Students);

This can then be passed to your ListView:

<ListView ItemsSource="{Binding Students}" IsGroupingEnabled="true" GroupDisplayBinding="{Binding Key.Name}">
    <ListView.ItemTemplate>
        <DataTemplate>
            <TextCell Text="{Binding Name}"/>
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>

And your models would look something like:

class Student : RealmObject
{
    public string Name { get; set; }
    
    public School School { get; set; }
}

class School : RealmObject
{
    public string Name { get; set; }
    
    [Backlink(nameof(Student.School))]
    public IQueryable<Student> Students { get; }
}

Features

Both the returned collection and the inner collections are observable, so any changes will update the UI.

Queries

// Return schools ordered by Name, containing Students ordered by Age
var students = realm.All<School>().OrderBy(school => school.Name)
                    .ToGroupedCollection(school => school.Students.OrderBy(student => student.Age));

Supported query operations are limited by Realm's query support.

To-many relationships

public class Dog : RealmObject
{
    public string Name { get; set; }
}

public class Person : RealmObject 
{
    public IList<Dog> Dogs { get; } 
}

var dogs = realm.All<Person>().ToGroupedCollection(person => person.Dogs);

Note that queries over IList properties are not supported and will result in a runtime exception. This is the case because those queries are executed by LINQ and not by Realm itself.

Using Backlinks to invert the group direction

Usually, a .NET grouping would go from the specific to the general:

IEnumerable<Student> students = ...;
var groupedStudents = students.GroupBy(s => s.School);

Since Realm doesn't yet support grouping, we can achieve the same result by using backlinks (inverse relationships).

Then, the grouping goes from the general to the specific:

IQueryable<School> schools = realm.All<School>();
var groupedStudents = schools.ToGroupedCollection(s => s.Students);

License

This project is released under the MIT license.