Fragments

It is possible to define and reuse fragments:

public static class UserFragments
{
    [GraphQLFragment]
    public static UserDetails ToUserDetails(this User user)
    {
        return new UserDetails
        {
            Id = user.Id,
            FirstName = user.FirstName,
            LastName = user.LastName
        };
    }
}

var variables = new { Id = 1 };
var response = await client.Query(
    variables,
    static (i, q) => 
        new 
        { 
            Me = q.Me(o => o.ToUserDetails()),
            User = q.User(i.Id, o => o.ToUserDetails())
        });


Console.WriteLine($"GraphQL: {response.Query}"); // GraphQL: query ($id: Int!) { me { id firstName lastName } user(id: $id) { id firstName lastName } }
Console.WriteLine($"{response.Data.Me.Id}: {response.Data.Me.FirstName} {response.Data.Me.LastName}"); // 1: Jon Smith
Console.WriteLine($"{response.Data.User.Id}: {response.Data.User.FirstName} {response.Data.User.LastName}"); // 1: Jon Smith

The fragment should be marked with the [GraphQLFragment] attribute, and it should be an extension method. If the fragment is defined in another assembly, it should be a partial method. The last requirement is necessary because source generators don't have access to source code from another assembly. So, a workaround will be to define fragments as a partial method and generate additional metadata.