Add comments + tests to delete_range()

src/db.rs

@@ -1649,9 +1649,13 @@ impl WriteBatch {
         }
     }
 
-    pub fn delete_range<K: AsRef<[u8]>>(&mut self, start_key: K,  end_key: K) -> Result<(), Error> {
+    /// Remove database entries from start key to end key.
-        let start_key = start_key.as_ref();
+    ///
-        let end_key = end_key.as_ref();
+    /// Removes the database entries in the range ["begin_key", "end_key"), i.e.,
+    /// including "begin_key" and excluding "end_key". It is not an error if no
+    /// keys exist in the range ["begin_key", "end_key").
+    pub fn delete_range<K: AsRef<[u8]>>(&mut self, start_key: K, end_key: K) -> Result<(), Error> {
+        let (start_key, end_key) = (start_key.as_ref(), end_key.as_ref());
 
         unsafe {
             ffi::rocksdb_writebatch_delete_range(
@@ -1665,9 +1669,13 @@ impl WriteBatch {
         }
     }
 
-    pub fn delete_range_cf<K: AsRef<[u8]>>(&mut self, cf: ColumnFamily, start_key: K,  end_key: K) -> Result<(), Error> {
+    pub fn delete_range_cf<K: AsRef<[u8]>>(
-        let start_key = start_key.as_ref();
+        &mut self,
-        let end_key = end_key.as_ref();
+        cf: ColumnFamily,
+        start_key: K,
+        end_key: K,
+    ) -> Result<(), Error> {
+        let (start_key, end_key) = (start_key.as_ref(), end_key.as_ref());
 
         unsafe {
             ffi::rocksdb_writebatch_delete_range_cf(
@@ -1978,7 +1986,9 @@ fn writebatch_works() {
             assert_eq!(batch.len(), 0);
             assert!(batch.is_empty());
             let _ = batch.put(b"k1", b"v1111");
-            assert_eq!(batch.len(), 1);
+            let _ = batch.put(b"k2", b"v2222");
+            let _ = batch.put(b"k3", b"v3333");
+            assert_eq!(batch.len(), 3);
             assert!(!batch.is_empty());
             assert!(db.get(b"k1").unwrap().is_none());
             let p = db.write(batch);
@@ -1996,6 +2006,17 @@ fn writebatch_works() {
             assert!(p.is_ok());
             assert!(db.get(b"k1").unwrap().is_none());
         }
+        {
+            // test delete_range
+            let mut batch = WriteBatch::default();
+            let _ = batch.delete_range(b"k2", b"k4");
+            assert_eq!(batch.len(), 1);
+            assert!(!batch.is_empty());
+            let p = db.write(batch);
+            assert!(p.is_ok());
+            assert!(db.get(b"k2").unwrap().is_none());
+            assert!(db.get(b"k3").unwrap().is_none());
+        }
         {
             // test size_in_bytes
             let mut batch = WriteBatch::default();