Helper to create Lamda expression to use in Linq-query when combining graphql-dotnet with entity framework and iqueryables.

GQLHelper.cs

using System;
using System.Linq;
using System.Linq.Expressions;
using GraphQL.Language.AST;
using GraphQL.Types;

public static class GQLHelper
{
    public static Expression<Func<T, T>> GraphQLFields<T>(ResolveFieldContext<object> ctx)
    {
        string fields = String.Join(",",ctx.FieldAst
                                .SelectionSet
                                .Selections
                                .Select(x => (x as Field).Name)
                                .ToArray());

        //Create new class of type T.
        var xNew = Expression.New(typeof(T));

        //Create parameter name for the LINQ/Lambda-expression.
        //Example: .Select(o => ...);
        var xParameter = Expression.Parameter(typeof(T), "o");

        //Iterate GraphQL query-fields and build properties to add to the body.
        var bindings = fields.Split(',').Select(o => o.Trim()).Select(o =>
        {
            var mi = typeof(T).GetProperties()
                    .Where(prop => prop.Name.ToLower() == o.ToLower())
                    .FirstOrDefault();

            if ((mi == null))
                return null;

            var xOriginal = Expression.Property(xParameter, mi);
            return Expression.Bind(mi, xOriginal);
        }).Where(s => s != null);

        var xInit = Expression.MemberInit(xNew, bindings);
        var lambda = Expression.Lambda<Func<T, T>>(xInit, xParameter);
        return lambda;
    }
}

I might improve this and publish as a nuget-package.