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Author: dotansimha

lib/query-planner/src/planner/fetch/selections.rs

@@ -125,9 +125,16 @@ impl<State> FetchStepSelections<State> {
         selection_set: SelectionSet,
         as_first: bool,
     ) {
+        println!(
+            "add_at_path_inner, definition_name: {}, fetch_path: {:?}",
+            definition_name, fetch_path
+        );
         let current = self
             .selections_for_definition_mut(&definition_name)
-            .expect("no selections declared for definition");
+            .expect(&format!(
+                "no selections declared for definition: {}",
+                definition_name
+            ));
 
         if let Some(selection_at_path) = find_selection_set_by_path_mut(current, fetch_path) {
             merge_selection_set(selection_at_path, &selection_set, as_first);
@@ -141,18 +148,24 @@ impl<State> FetchStepSelections<State> {
 }
 
 impl FetchStepSelections<MultiTypeFetchStep> {
+    pub fn try_as_single(&self) -> Option<&str> {
+        if self.selections.len() == 1 {
+            self.selections.keys().next().map(|key| key.as_str())
+        } else {
+            None
+        }
+    }
+
     pub fn iter_selections(&self) -> impl Iterator<Item = (&String, &SelectionSet)> {
         self.selections.iter()
     }
 
     pub fn migrate_from_another(&mut self, other: &Self, fetch_path: &MergePath) {
-        for (definition_name, selection_set) in other.iter_selections() {
-            println!(
-                "migrate_from_another, fetch_path: {}, definition_name={}",
-                fetch_path, definition_name
-            );
+        let maybe_merge_into = self.try_as_single().map(|str| str.to_string());
 
-            self.add_at_path_inner(definition_name, fetch_path, selection_set.clone(), false);
+        for (definition_name, selection_set) in other.iter_selections() {
+            let target_type = maybe_merge_into.as_ref().unwrap_or(definition_name);
+            self.add_at_path_inner(&target_type, fetch_path, selection_set.clone(), false);
         }
     }