Simplify handling of NotFound SQL errors (fixes #4633)

crates/api_crud/src/post/read.rs

@@ -40,10 +40,7 @@ pub async fn get_post(
   };
 
   // Check to see if the person is a mod or admin, to show deleted / removed
-  let community_id = Post::read(&mut context.pool(), post_id)
+  let community_id = Post::read_xx(&mut context.pool(), post_id).await?.community_id;
-    .await?
-    .ok_or(LemmyErrorType::CouldntFindPost)?
-    .community_id;
 
   let is_mod_or_admin = is_mod_or_admin_opt(
     &mut context.pool(),

crates/db_schema/src/impls/post.rs

@@ -68,6 +68,10 @@ impl Crud for Post {
 }
 
 impl Post {
+  pub async fn read_xx(pool: &mut DbPool<'_>, id: PostId) -> Result<Self, Error> {
+    let conn = &mut *get_conn(pool).await?;
+    post::table.find(id).first(conn).await
+  }
   pub async fn insert_apub(
     pool: &mut DbPool<'_>,
     timestamp: DateTime<Utc>,

crates/utils/src/error.rs

@@ -211,8 +211,12 @@ cfg_if! {
     {
       fn from(t: T) -> Self {
         let cause = t.into();
+        let error_type = match cause.downcast_ref::<diesel::result::Error>() {
+          Some(&diesel::NotFound) => LemmyErrorType::CouldntFindPost,
+          _ => LemmyErrorType::Unknown(format!("{}", &cause))
+      };
         LemmyError {
-          error_type: LemmyErrorType::Unknown(format!("{}", &cause)),
+          error_type,
           inner: cause,
           context: Backtrace::capture(),
         }
@@ -323,6 +327,17 @@ cfg_if! {
         )
       }
 
+      #[test]
+      fn test_convert_diesel_errors() {
+        let not_found_error = LemmyError::from(diesel::NotFound);
+        assert_eq!(LemmyErrorType::CouldntFindPost, not_found_error.error_type);
+        assert_eq!(404, not_found_error.status_code());
+
+        let other_error = LemmyError::from(diesel::result::Error::NotInTransaction);
+        assert!(matches!(other_error.error_type, LemmyErrorType::Unknown{..}));
+        assert_eq!(400, other_error.status_code());
+      }
+
       /// Check if errors match translations. Disabled because many are not translated at all.
       #[test]
       #[ignore]