graphql.cs

private static string ToString(IContainer container, IFieldType field, Type toResolve, int deep) =>
    toResolve.IsAssignableTo<IComplexGraphType>()
        ? ToStringAsField(container, field, toResolve, deep, FieldFormat)
        : ToStringAsUnion(container, field, toResolve, deep);

private static string FormatWithPropertiesForUnions(IContainer container, IFieldType field, Type toResolve, int deep)
{
    var unionTypes = (UnionGraphType) container.Resolve(toResolve);
    var unions = unionTypes.Types
        .Select(type => FormatAsField(container, field, type, deep, UnionFormat));
    return string.Join("", unions);
}

private static string FormatAsField(
    IContainer container, 
    IFieldType field, 
    Type toResolve, 
    int deep, 
    Func<string, string, string, string> format
)
{
    var type = (IComplexGraphType) container.Resolve(toResolve);
    var fields = string.Join(' ', type.Fields.Select(y => ToString(y, container, deep 1)));
    return string.IsNullOrWhiteSpace(fields)
        ? string.Empty
        : format(field.Name, type.Name, fields);
}
 
private static string FieldFormat(string fieldName, string _, string fields) =>
    $"{fieldName}{{{fields}}}";

private static string UnionFormat(string fieldName, string unionName, string fields) =>
    $"{fieldName}{{ ... on {unionName}{{{fields}}}}}";