Merge pull request #229 from andylokandy/exist

Add key_exists method

README.md

@@ -74,8 +74,10 @@ There are some [examples](examples) which show how to use the client in a Rust p
 | ----------- | ------------------- | ---------------------- | ------------------------------------------------------------------ |
 | `put`       | `KvPair`            | `()`                   |                                                                    |
 | `get`       | `Key`               | `Option<value>`        |                                                                    |
+| `key_exists` | `Key`               | `bool`                 |                                                                    |
 | `delete`    | `Key`               | `()`                   |                                                                    |
 | `scan`      | `BoundRange`        | `Iter<KvPair>`         |                                                                    |
+| `scan_keys` | `BoundRange`        | `Iter<Key>`            |                                                                    |
 | `batch_get` | `Iter<Key>`         | `Iter<KvPair>`         | Skip non-existent keys; Does not retain order                      |
 | `lock_keys` | `Iter<Key>`         | `()`                   |                                                                    |
 | `gc`        | `Timestamp`         | `bool`                 | It returns whether the latest safepoint in PD equals the parameter |

examples/transaction.rs

@@ -29,6 +29,21 @@ async fn get(client: &Client, key: Key) -> Option<Value> {
     res
 }
 
+async fn key_exists(client: &Client, key: Key) -> bool {
+    let mut txn = client
+        .begin_optimistic()
+        .await
+        .expect("Could not begin a transaction");
+    let res = txn
+        .key_exists(key)
+        .await
+        .expect("Could not check key exists");
+    txn.commit()
+        .await
+        .expect("Committing read-only transaction should not fail");
+    res
+}
+
 async fn scan(client: &Client, range: impl Into<BoundRange>, limit: u32) {
     let mut txn = client
         .begin_optimistic()
@@ -82,6 +97,16 @@ async fn main() {
     let value1 = get(&txn, key1.clone()).await;
     println!("{:?}", (key1, value1));
 
+    // check key exists
+    let key1: Key = b"key1".to_vec().into();
+    let key1_exists = key_exists(&txn, key1.clone()).await;
+    let key2: Key = b"key_not_exist".to_vec().into();
+    let key2_exists = key_exists(&txn, key2.clone()).await;
+    println!(
+        "check exists {:?}",
+        vec![(key1, key1_exists), (key2, key2_exists)]
+    );
+
     // scan
     let key1: Key = b"key1".to_vec().into();
     scan(&txn, key1.., 10).await;

src/transaction/snapshot.rs

@@ -23,6 +23,11 @@ impl Snapshot {
         self.transaction.get(key).await
     }
 
+    /// Check whether the key exists.
+    pub async fn key_exists(&self, key: impl Into<Key>) -> Result<bool> {
+        self.transaction.key_exists(key).await
+    }
+
     /// Get the values associated with the given keys.
     pub async fn batch_get(
         &self,

src/transaction/transaction.rs

@@ -146,6 +146,24 @@ impl Transaction {
         }
     }
 
+    /// Check whether the key exists.
+    ///
+    /// # Examples
+    /// ```rust,no_run
+    /// # use tikv_client::{Value, Config, TransactionClient};
+    /// # use futures::prelude::*;
+    /// # futures::executor::block_on(async {
+    /// # let client = TransactionClient::new(vec!["192.168.0.100", "192.168.0.101"]).await.unwrap();
+    /// let mut txn = client.begin_pessimistic().await.unwrap();
+    /// let exists = txn.key_exists("k1".to_owned()).await.unwrap();
+    /// txn.commit().await.unwrap();
+    /// # });
+    /// ```
+    pub async fn key_exists(&self, key: impl Into<Key>) -> Result<bool> {
+        let key = key.into();
+        Ok(self.scan_keys(key.clone()..=key, 1).await?.next().is_some())
+    }
+
     /// Create a new 'batch get' request.
     ///
     /// Once resolved this request will result in the fetching of the values associated with the