What have you done with UDAs?

[via Digitalmars-d]

I use them in a simple MongoDB-based ORM, not (yet?) publically 
available. Usage is like this:

@Collection("my.model")
struct MyModel {
     @Field @Required @Index
     BsonObjectID foreignKey;

     @Field
     string someOptionalString;
     @Field @Required
     int[] someRequiredArray;

     @Field @Validate!(a => a % 2 != 0)
     int onlyOddIntegers;
     @Field @ValidEmail
     string email;

     mixin ORM;
}