Move count() to CountTrait

sea-orm-sync/src/executor/paginator.rs

@@ -87,11 +87,7 @@ where
             Some(res) => res,
             None => return Ok(0),
         };
-        #[allow(clippy::match_single_binding)]
-        let num_items = match self.db.get_database_backend() {
-            _ => result.try_get::<i64>("", "num_items")? as u64,
-        };
-        Ok(num_items)
+        Ok(result.try_get::<i64>("", "num_items")? as u64)
     }
 
     /// Get the total number of pages
@@ -272,12 +268,30 @@ where
     /// Paginate the result of a select operation.
     fn paginate(self, db: &'db C, page_size: u64) -> Paginator<'db, C, Self::Selector>;
 
-    /// Perform a count on the paginated results
+    /// Count the number of rows this query selects, honoring any `limit` and
+    /// `offset` set on it.
+    ///
+    /// This differs from [`Paginator::num_items`], which resets `limit`/`offset`
+    /// to report the grand total for pagination. `count` wraps the query as-is in
+    /// a `SELECT COUNT(*) FROM (..)` subquery, so a query with a `limit` counts at
+    /// most that many rows.
     fn count(self, db: &'db C) -> Result<u64, DbErr>
     where
         Self: Sized,
     {
-        self.paginate(db, 1).num_items()
+        let paginator = self.paginate(db, 1);
+        let query = SelectStatement::new()
+            .expr(Expr::cust("COUNT(*) AS num_items"))
+            .from_subquery(
+                paginator.query.clone().clear_order_by().to_owned(),
+                "sub_query",
+            )
+            .to_owned();
+        let result = match db.query_one(&query)? {
+            Some(res) => res,
+            None => return Ok(0),
+        };
+        Ok(result.try_get::<i64>("", "num_items")? as u64)
     }
 }
 

sea-orm-sync/src/executor/select_ext.rs

@@ -4,7 +4,6 @@ use crate::{
 };
 use sea_query::{Expr, SelectStatement};
 
-// TODO: Move count here
 /// Helper trait for selectors with convenient methods
 pub trait SelectExt {
     /// This method is unstable and is only used for internal testing.

sea-orm-sync/tests/paginator_tests.rs

@@ -4,7 +4,7 @@ pub mod common;
 
 pub use common::{TestContext, features::*, setup::*};
 use pretty_assertions::assert_eq;
-use sea_orm::{PaginatorTrait, QueryOrder, Set, entity::prelude::*};
+use sea_orm::{PaginatorTrait, QueryOrder, QuerySelect, Set, entity::prelude::*};
 
 #[sea_orm_macros::test]
 fn paginator_tests() -> Result<(), DbErr> {
@@ -145,5 +145,10 @@ pub fn paginator_count(db: &DatabaseConnection) -> Result<(), DbErr> {
 
     assert_eq!(Entity::find().filter(Column::Id.gt(100)).count(db)?, 0);
 
+    // `count` honors `limit`/`offset` set on the query, unlike `num_items`.
+    assert_eq!(Entity::find().limit(3).count(db)?, 3);
+
+    assert_eq!(Entity::find().limit(4).offset(8).count(db)?, 2);
+
     Ok(())
 }

src/executor/paginator.rs

@@ -89,11 +89,7 @@ where
             Some(res) => res,
             None => return Ok(0),
         };
-        #[allow(clippy::match_single_binding)]
-        let num_items = match self.db.get_database_backend() {
-            _ => result.try_get::<i64>("", "num_items")? as u64,
-        };
-        Ok(num_items)
+        Ok(result.try_get::<i64>("", "num_items")? as u64)
     }
 
     /// Get the total number of pages
@@ -279,12 +275,30 @@ where
     /// Paginate the result of a select operation.
     fn paginate(self, db: &'db C, page_size: u64) -> Paginator<'db, C, Self::Selector>;
 
-    /// Perform a count on the paginated results
+    /// Count the number of rows this query selects, honoring any `limit` and
+    /// `offset` set on it.
+    ///
+    /// This differs from [`Paginator::num_items`], which resets `limit`/`offset`
+    /// to report the grand total for pagination. `count` wraps the query as-is in
+    /// a `SELECT COUNT(*) FROM (..)` subquery, so a query with a `limit` counts at
+    /// most that many rows.
     async fn count(self, db: &'db C) -> Result<u64, DbErr>
     where
         Self: Send + Sized,
     {
-        self.paginate(db, 1).num_items().await
+        let paginator = self.paginate(db, 1);
+        let query = SelectStatement::new()
+            .expr(Expr::cust("COUNT(*) AS num_items"))
+            .from_subquery(
+                paginator.query.clone().clear_order_by().to_owned(),
+                "sub_query",
+            )
+            .to_owned();
+        let result = match db.query_one(&query).await? {
+            Some(res) => res,
+            None => return Ok(0),
+        };
+        Ok(result.try_get::<i64>("", "num_items")? as u64)
     }
 }
 

src/executor/select_ext.rs

@@ -4,7 +4,6 @@ use crate::{
 };
 use sea_query::{Expr, SelectStatement};
 
-// TODO: Move count here
 #[async_trait::async_trait]
 /// Helper trait for selectors with convenient methods
 pub trait SelectExt {

tests/paginator_tests.rs

@@ -4,7 +4,7 @@ pub mod common;
 
 pub use common::{TestContext, features::*, setup::*};
 use pretty_assertions::assert_eq;
-use sea_orm::{PaginatorTrait, QueryOrder, Set, entity::prelude::*};
+use sea_orm::{PaginatorTrait, QueryOrder, QuerySelect, Set, entity::prelude::*};
 
 #[sea_orm_macros::test]
 async fn paginator_tests() -> Result<(), DbErr> {
@@ -149,5 +149,10 @@ pub async fn paginator_count(db: &DatabaseConnection) -> Result<(), DbErr> {
         0
     );
 
+    // `count` honors `limit`/`offset` set on the query, unlike `num_items`.
+    assert_eq!(Entity::find().limit(3).count(db).await?, 3);
+
+    assert_eq!(Entity::find().limit(4).offset(8).count(db).await?, 2);
+
     Ok(())
 }