Implement ApplyOffset for diesel::mysql::Mysq

Author: Alexei Pastuchov

wundergraph/src/query_builder/selection/offset.rs

@@ -1,15 +1,16 @@
 use crate::error::Result;
-#[cfg(any(feature = "postgres", feature = "sqlite"))]
+#[cfg(any(feature = "postgres", feature = "sqlite", feature = "mysql"))]
 use crate::error::WundergraphError;
-#[cfg(any(feature = "postgres", feature = "sqlite"))]
+#[cfg(any(feature = "postgres", feature = "sqlite", feature = "mysql"))]
 use crate::juniper_ext::FromLookAheadValue;
 use crate::query_builder::selection::{BoxedQuery, LoadingHandler};
 use crate::scalar::WundergraphScalarValue;
 use diesel::backend::Backend;
 #[cfg(feature = "sqlite")]
 use diesel::query_dsl::methods::LimitDsl;
-#[cfg(any(feature = "postgres", feature = "sqlite"))]
+#[cfg(any(feature = "postgres", feature = "sqlite", feature = "mysql"))]
 use diesel::query_dsl::methods::OffsetDsl;
+
 use juniper::LookAheadSelection;
 
 /// A trait abstracting over the different behaviour of limit/offset
@@ -72,3 +73,25 @@ impl ApplyOffset for diesel::sqlite::Sqlite {
         }
     }
 }
+
+#[cfg(feature = "mysql")]
+impl ApplyOffset for diesel::mysql::Mysql {
+    fn apply_offset<'a, L, Ctx>(
+        query: BoxedQuery<'a, L, Self, Ctx>,
+        select: &LookAheadSelection<'_, WundergraphScalarValue>,
+    ) -> Result<BoxedQuery<'a, L, Self, Ctx>>
+    where
+        L: LoadingHandler<Self, Ctx>,
+    {
+        use juniper::LookAheadMethods;
+        if let Some(offset) = select.argument("offset") {
+            Ok(<_ as OffsetDsl>::offset(
+                query,
+                i64::from_look_ahead(offset.value())
+                    .ok_or(WundergraphError::CouldNotBuildFilterArgument)?,
+            ))
+        } else {
+            Ok(query)
+        }
+    }
+}