Sorting

Being able to sort or order you collections as you query them can be very powerful, especially when paired with paging. To easily add sorting functionality to your collection fields use the UseSort() field extension.

Note: When using with one of the paging extensions ensure you call UseSort first. If you are using the attribute, then ensure the Sort attribute comes before the paging attribute. If using with the UseFilter extensions, call filter first. Filter -> Sort -> Paging.

schema.ReplaceField("people",
    ctx => ctx.People,
    "Return a list of people. Optional sorted")
    .UseSort();

If you are using the SchemaBuilder.FromObject you can use the UseSortAttribute on your collection properties.

public class DemoContext : DbContext
{
    [UseSort]
    public DbSet<Movie> Movies { get; set; }
    [UseSort]
    public DbSet<Person> People { get; set; }
    [UseSort]
    public DbSet<Actor> Actors { get; set; }
}

This field extension can only be used on a field that has a Resolve expression that is assignable to IEnumerable - I.e. collections. The extension adds an argument called sort: [<field_name>SortInput]. For example PeopleSortInput. The SortInput type will have nullable fields for each scalar type in the collection element type. You set which fields you want to use for sorting. Following the above people field with the Person class defined as:

public class Person
{
    public uint Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public DateTime Dob { get; set; }v
    public List<Actor> ActorIn { get; set; }
    public List<Writer> WriterOf { get; set; }
    public List<Movie> DirectorOf { get; set; }
    public DateTime? Died { get; set; }
    public bool IsDeleted { get; set; }
}

The GraphQL type will be define like:

input PeopleSortInput
{
	id: SortDirectionEnum
	firstName: SortDirectionEnum
	lastName: SortDirectionEnum
	dob: SortDirectionEnum
	died: SortDirectionEnum
	isDeleted: SortDirectionEnum
}

enum SortDirectionEnum {
	ASC
	DESC
}

To sort the collection you set the fields with a direction:

{
  people(sort: [{ lastName: DESC }]) {
    lastName
  }
}

{
  people(sort: [{ dob: ASC }]) {
    lastName
  }
}

Multiple fields is supported and are taken as ordered

{
  people(sort: [{ dob: ASC }, { lastName: DESC }, { firstName: ASC }]) {
    lastName
  }
}

Default sort

You can set a default sort to be applied if there are no sort arguments passed in the query.

schema.ReplaceField("people",
    ctx => ctx.People,
    "Return a list of people. Optional sorted")
    .UseSort((Person person) => person.Dob, SortDirectionEnum.DESC);

Default with multiple field

schema.ReplaceField("people",
    ctx => ctx.People,
    "Return a list of people. Optional sorted")
    .UseSort(
        new Sort<Person>((person) => person.Height, SortDirection.ASC),
        new Sort<Person>((person) => person.LastName, SortDirection.ASC)
    );

Choosing the sort fields

If you use the UseSort() method (not the attribute) you can pass in an expression which tells the extension which fields to set in the input type. Make sure you use the correct type for the fields collection. You can still set the default sort as well.

schema.ReplaceField("people",
    ctx => ctx.People,
    "Return a list of people. Optional sorted")
    // available sort fields
    .UseSort((Person person) => new
    {
        person.Dob,
        person.LastName
    },
    // Default sort
    (Person person) => person.Dob, SortDirectionEnum.DESC);

This will result in only 2 options for sorting.

input PeopleSortInput {
  dob: SortDirectionEnum
  lastName: SortDirectionEnum
}