better validation

src/model/valid.rs

@@ -1,19 +1,29 @@
 /// This trait allows a `Model` to be validated.
 pub trait Validate {
     /// Validate the `Model`
-    fn validate(&self) -> impl std::future::Future<Output = bool> + Send;
+    fn validate(&self) -> impl std::future::Future<Output = Result<(), String>> + Send;
 }
 
-/// Validate a value and return `false` if validation fails.
+/// Validate a value and return an Error if validation fails.
 #[macro_export]
 macro_rules! validate {
     ($val:expr) => {
-        if !$val.validate().await {
-            return false;
+        if let Err(err) = $val.validate().await {
+            return Err(format!("{}: {}", stringify!($val), err));
         }
     };
 }
 
+#[macro_export]
+macro_rules! count_items {
+    // Base case: single item
+    ($single:ident) => { 1 };
+    // Recursive case: count each item
+    ($head:ident, $($tail:ident),*) => {
+        1 + mongod::count_items!($($tail),*)
+    };
+}
+
 /// This macro checks for the type of a reference and is useful for validation.
 /// It will check all supplied types and return `false` if none are matching.
 ///
@@ -34,7 +44,10 @@ macro_rules! assert_reference_of {
             }
         )*
         if !match_found {
-            return false;
+            let possible_types: [&str; mongod::count_items!($($struct_name),*)] = [
+                $(stringify!($struct_name)),*
+            ];
+            return Err(format!("{} is not of any type: {:?}", stringify!($var), possible_types));
         }
     };
 }