Query Mode: Having _exists set in query mode when required data type is defined by schema

[hhhapz]

When generating a custom query method, sometimes the value returned is identical to a defined type already in the schema, but may contain something such as a simple join which makes not possible to be used alongside an index. In these situations, using -2 (Second mode) and --append is very handy, and allows for returning the same schema returned type, however unfortunately the _exists flag is not added.

Of course, this will be difficult to implement "fully" correctly, as I do not believe there is a definitive way to make sure that such a flag does indeed exist within that field. The easiest way to implement this would be via a flag, undecided on a name that fits,

With the proposed custom project mode, there may also be the ability to do this when all the queries alongside the types are known, however for such a feature this may be over complicating the build steps for queries.