Macro struct_to_json_db::db_relation_add

macro_rules! db_relation_add {
    ($first:ident=$first_val:literal, $second:ident=$second_val:literal) => { ... };
    ($first:ident=$first_val:expr, $second:ident=$second_val:expr, weight=$weight_val:expr) => { ... };
    ($first:ident=$first_val:expr, $second:ident=$second_val:expr, name=$name_val:expr) => { ... };
    ($first:ident=$first_val:expr, $second:ident=$second_val:expr, name=$name_val:expr,weight=$weight_val:expr) => { ... };
}