fix(mongodb): avoid exact count for unfiltered queries

crates/dbx-core/src/db/document_result.rs

@@ -47,4 +47,18 @@ mod tests {
         .unwrap();
         assert!(deserialized.total_is_exact);
     }
+
+    #[test]
+    fn inexact_results_preserve_the_explicit_flag() {
+        let deserialized: DocumentQueryResult = serde_json::from_value(serde_json::json!({
+            "documents": [],
+            "total": 10_000_000,
+            "total_is_exact": false,
+        }))
+        .unwrap();
+        assert!(!deserialized.total_is_exact);
+
+        let serialized = serde_json::to_value(deserialized).unwrap();
+        assert_eq!(serialized.get("total_is_exact"), Some(&serde_json::json!(false)));
+    }
 }

crates/dbx-core/src/db/mongo_driver.rs

@@ -637,10 +637,11 @@ pub async fn find_documents(
         _ => doc! {},
     };
 
-    let total = if filter_doc.is_empty() {
-        col.estimated_document_count().await.map_err(|e| e.to_string())?
-    } else {
+    let total_is_exact = !filter_doc.is_empty();
+    let total = if total_is_exact {
         col.count_documents(filter_doc.clone()).await.map_err(|e| e.to_string())?
+    } else {
+        col.estimated_document_count().await.map_err(|e| e.to_string())?
     };
 
     let mut find = col.find(filter_doc).skip(skip).limit(limit);
@@ -675,7 +676,7 @@ pub async fn find_documents(
         raw_documents: None,
         extended_documents: Some(extended_documents),
         total,
-        total_is_exact: true,
+        total_is_exact,
     })
 }
 
@@ -781,10 +782,11 @@ pub async fn find_documents_extended_json(
         _ => doc! {},
     };
 
-    let total = if filter_doc.is_empty() {
-        col.estimated_document_count().await.map_err(|e| e.to_string())?
-    } else {
+    let total_is_exact = !filter_doc.is_empty();
+    let total = if total_is_exact {
         col.count_documents(filter_doc.clone()).await.map_err(|e| e.to_string())?
+    } else {
+        col.estimated_document_count().await.map_err(|e| e.to_string())?
     };
 
     let mut find = col.find(filter_doc).skip(skip).limit(limit);
@@ -820,7 +822,7 @@ pub async fn find_documents_extended_json(
         documents,
         raw_documents: None,
         total,
-        total_is_exact: true,
+        total_is_exact,
     })
 }