Don't include Identifiable in db_type if no id field

src/lib.rs

@@ -30,6 +30,11 @@ pub fn db_type(attr: TokenStream, item: TokenStream) -> TokenStream {
         .into();
     };
 
+    let has_id_field = fields.named.iter().any(|field|
+        field.ident.as_ref()
+            .map_or(false, |field| field == "id")
+    );
+
     // Filter out fields with the `#[omit_new]` attribute
     let new_fields = fields.named.iter().filter(|field| {
         !field
@@ -89,12 +94,23 @@ pub fn db_type(attr: TokenStream, item: TokenStream) -> TokenStream {
     // Get the table path from the attribute
     let table_path = parse_macro_input!(attr as Path);
 
-    // Generate the expanded code
-    let expanded = quote! {
-        #[cfg_attr(feature = "ssr", derive(
+    // Don't include the Identifiable derive for structs without an `id` field
+    let full_type_derives = if has_id_field {
+        quote! {
             diesel::prelude::Queryable,
             diesel::prelude::Selectable,
-            diesel::prelude::Identifiable))]
+            diesel::prelude::Identifiable
+        }
+    } else {
+        quote! {
+            diesel::prelude::Queryable,
+            diesel::prelude::Selectable
+        }
+    };
+
+    // Generate the expanded code
+    let expanded = quote! {
+        #[cfg_attr(feature = "ssr", derive(#full_type_derives))]
         #[cfg_attr(feature = "ssr", diesel(check_for_backend(diesel::pg::Pg)))]
         #[cfg_attr(feature = "ssr", diesel(table_name = #table_path))]
         #clean_derive_input