Removing fields with ITypeRewriter

RemoveFieldsRewriter.cs

using System;
using System.Collections.Generic;
using System.Linq;
using HotChocolate.Language;
using HotChocolate.Stitching.Merge;
using HotChocolate.Stitching.Merge.Rewriters;
using HotChocolate.Types;

namespace MyCompany.GraphQLService.Stitching
{
    internal class RemoveFieldsRewriter : ITypeRewriter
    {
        public ITypeDefinitionNode Rewrite(ISchemaInfo schema, ITypeDefinitionNode typeDefinition)
        {
            if (schema.Name.HasValue &&
                typeDefinition is ObjectTypeDefinitionNode otd)
            {
                return RemoveFields(schema.Name, otd, _shouldKeepCheck, f => otd.WithFields(f));
            }

            return typeDefinition;
        }

        private static readonly Func<string, FieldDefinitionNode, bool> _shouldKeepCheck = (schemaName, field) =>
            _someListOfFieldsYouWantToKeepMaybeLoadedFromExternalFile.Contains(field.Name.Value);

        private static T RemoveFields<T>(
            string schemaName,
            T typeDefinition,
            Func<string, FieldDefinitionNode, bool> shouldKeep,
            RewriteFieldsDelegate<T> rewrite)
            where T : ComplexTypeDefinitionNodeBase, ITypeDefinitionNode
        {
            var keptFields = new List<FieldDefinitionNode>();

            foreach (var field in typeDefinition.Fields)
            {
                if (shouldKeep(schemaName, field))
                {
                    keptFields.Add(field);
                }
            }

            return rewrite(keptFields);
        }

        internal delegate T RewriteFieldsDelegate<T>(
            IReadOnlyList<FieldDefinitionNode> fields)
            where T : ComplexTypeDefinitionNodeBase, ITypeDefinitionNode;
    }
}