support writebatch is_empty

src/rocksdb.rs

@@ -964,6 +964,10 @@ impl WriteBatch {
     pub fn count(&self) -> usize {
         unsafe { rocksdb_ffi::rocksdb_writebatch_count(self.inner) as usize }
     }
+
+    pub fn is_empty(&self) -> bool {
+        self.count() == 0
+    }
 }
 
 impl Drop for WriteBatch {
@@ -1167,8 +1171,10 @@ mod test {
         let batch = WriteBatch::new();
         assert!(db.get(b"k1").unwrap().is_none());
         assert_eq!(batch.count(), 0);
+        assert!(batch.is_empty());
         let _ = batch.put(b"k1", b"v1111");
         assert_eq!(batch.count(), 1);
+        assert!(!batch.is_empty());
         assert!(db.get(b"k1").unwrap().is_none());
         let p = db.write(batch);
         assert!(p.is_ok());
@@ -1179,6 +1185,7 @@ mod test {
         let batch = WriteBatch::new();
         let _ = batch.delete(b"k1");
         assert_eq!(batch.count(), 1);
+        assert!(!batch.is_empty());
         let p = db.write(batch);
         assert!(p.is_ok());
         assert!(db.get(b"k1").unwrap().is_none());