From 5a6acd67312601e4dba32896600044950e20f99f Mon Sep 17 00:00:00 2001
From: Chris Tsang <chris.2y3@outlook.com>
Date: Fri, 22 Sep 2023 17:31:15 +0100
Subject: [PATCH] Fix loader panic on empty

---
 src/executor/cursor.rs |  1 -
 src/query/loader.rs    | 31 +++++++++++++++++--------------
 2 files changed, 17 insertions(+), 15 deletions(-)

diff --git a/src/executor/cursor.rs b/src/executor/cursor.rs
index 494957fa..50f282ef 100644
--- a/src/executor/cursor.rs
+++ b/src/executor/cursor.rs
@@ -382,7 +382,6 @@ where
 #[cfg(test)]
 #[cfg(feature = "mock")]
 mod tests {
-    use super::*;
     use crate::entity::prelude::*;
     use crate::tests_cfg::*;
     use crate::{DbBackend, MockDatabase, Statement, Transaction};
diff --git a/src/query/loader.rs b/src/query/loader.rs
index 2f3693a3..c615b4e4 100644
--- a/src/query/loader.rs
+++ b/src/query/loader.rs
@@ -143,6 +143,10 @@ where
             return Err(query_err("Relation is HasMany instead of HasOne"));
         }
 
+        if self.is_empty() {
+            return Ok(Vec::new());
+        }
+
         let keys: Vec<ValueTuple> = self
             .iter()
             .map(|model: &M| extract_key(&rel_def.from_col, model))
@@ -194,6 +198,10 @@ where
             return Err(query_err("Relation is HasOne instead of HasMany"));
         }
 
+        if self.is_empty() {
+            return Ok(Vec::new());
+        }
+
         let keys: Vec<ValueTuple> = self
             .iter()
             .map(|model: &M| extract_key(&rel_def.from_col, model))
@@ -269,6 +277,10 @@ where
                 )));
             }
 
+            if self.is_empty() {
+                return Ok(Vec::new());
+            }
+
             let pkeys: Vec<ValueTuple> = self
                 .iter()
                 .map(|model: &M| extract_key(&via_rel.from_col, model))
@@ -587,14 +599,11 @@ mod tests {
         );
     }
 
-    // FIXME: load many with empty vector will panic
-    // #[tokio::test]
+    #[tokio::test]
     async fn test_load_many_empty() {
         use sea_orm::{entity::prelude::*, tests_cfg::*, DbBackend, MockDatabase};
 
-        let db = MockDatabase::new(DbBackend::Postgres)
-            .append_query_results([[fruit_model(1, Some(1)), fruit_model(2, Some(1))]])
-            .into_connection();
+        let db = MockDatabase::new(DbBackend::Postgres).into_connection();
 
         let cakes: Vec<cake::Model> = vec![];
 
@@ -610,9 +619,7 @@ mod tests {
 
     #[tokio::test]
     async fn test_load_many_to_many_base() {
-        use sea_orm::{
-            entity::prelude::*, tests_cfg::*, DbBackend, IntoMockRow, LoaderTrait, MockDatabase,
-        };
+        use sea_orm::{tests_cfg::*, DbBackend, IntoMockRow, LoaderTrait, MockDatabase};
 
         let db = MockDatabase::new(DbBackend::Postgres)
             .append_query_results([
@@ -633,9 +640,7 @@ mod tests {
 
     #[tokio::test]
     async fn test_load_many_to_many_complex() {
-        use sea_orm::{
-            entity::prelude::*, tests_cfg::*, DbBackend, IntoMockRow, LoaderTrait, MockDatabase,
-        };
+        use sea_orm::{tests_cfg::*, DbBackend, IntoMockRow, LoaderTrait, MockDatabase};
 
         let db = MockDatabase::new(DbBackend::Postgres)
             .append_query_results([
@@ -675,9 +680,7 @@ mod tests {
 
     #[tokio::test]
     async fn test_load_many_to_many_empty() {
-        use sea_orm::{
-            entity::prelude::*, tests_cfg::*, DbBackend, IntoMockRow, LoaderTrait, MockDatabase,
-        };
+        use sea_orm::{tests_cfg::*, DbBackend, IntoMockRow, LoaderTrait, MockDatabase};
 
         let db = MockDatabase::new(DbBackend::Postgres)
             .append_query_results([