I want to call MarriageById
as GET, like this:
var url = \'/MarriageById?id=\' + id;
But I also want to have a single Action
I don't think you should mix GET with POST verbs. They are just semantically different. If you have a similar functionality that you want to execute for those 2 methods, maybe instead of calling POST from GET you might want to extract the common parts ot some other 'private' method or even layer (depending on the use case).
Hope it makes sense