Using the Key/Value Store

As the Key Value Store is built on top of the JetStream persistence layer you obtain a KeyValueManager object from your JetStream context.

The key must be in the same format as a NATS subject, i.e. it can be a dot separated list of tokens (which means that you can then use wildcards to match hierarchies of keys when watching a bucket), and can only contain valid characters. The value can be any byte array.

Creating, and deleting KV buckets

You can create as many independent key/value store instance, called 'buckets', as you need. Buckets are typically created, purged or deleted administratively (e.g. using the nats CLI tool), but this can also be done using one of the following KeyValueManager calls:

Go

// KeyValue will lookup and bind to an existing KeyValue store.
KeyValue(bucket string) (KeyValue, error)
// CreateKeyValue will create a KeyValue store with the following configuration.
CreateKeyValue(cfg *KeyValueConfig) (KeyValue, error)
// DeleteKeyValue will delete this KeyValue store (JetStream stream).
DeleteKeyValue(bucket string) error

Java

/**
 * Create a key value store.
 * @param config the key value configuration
 * @return bucket info
 * @throws IOException covers various communication issues with the NATS
 *         server such as timeout or interruption
 * @throws JetStreamApiException the request had an error related to the data
 * @throws IllegalArgumentException the server is not JetStream enabled
 */
KeyValueStatus create(KeyValueConfiguration config) throws IOException, JetStreamApiException;

/**
* Get the list of bucket names.
* @return list of bucket names
* @throws IOException covers various communication issues with the NATS
*         server such as timeout or interruption
* @throws JetStreamApiException the request had an error related to the data
* @throws InterruptedException if the thread is interrupted
*/
List<String> getBucketNames() throws IOException, JetStreamApiException, InterruptedException;

/**
* Gets the info for an existing bucket.
* @param bucketName the bucket name to use
* @throws IOException covers various communication issues with the NATS
*         server such as timeout or interruption
* @throws JetStreamApiException the request had an error related to the data
* @return the bucket status object
*/
KeyValueStatus getBucketInfo(String bucketName) throws IOException, JetStreamApiException;

/**
* Deletes an existing bucket. Will throw a JetStreamApiException if the delete fails.
* @param bucketName the stream name to use.
* @throws IOException covers various communication issues with the NATS
*         server such as timeout or interruption
* @throws JetStreamApiException the request had an error related to the data
*/
void delete(String bucketName) throws IOException, JetStreamApiException;

JavaScript

  static async create(
    js: JetStreamClient,
    name: string,
    opts: Partial<KvOptions> = {},
  ): Promise<KV>

static async bind(
    js: JetStreamClient,
    name: string,
    opts: Partial<{ codec: KvCodecs }> = {},
): Promise<KV>

destroy(): Promise<boolean>

Python

# from the JetStreamContext

async def key_value(self, bucket: str) -> KeyValue:

async def create_key_value(
    self,
    config: Optional[api.KeyValueConfig] = None,
    **params,
) -> KeyValue:
    """
    create_key_value takes an api.KeyValueConfig and creates a KV in JetStream.
    """
    
async def delete_key_value(self, bucket: str) -> bool:
    """
    delete_key_value deletes a JetStream KeyValue store by destroying
    the associated stream.
    """  

C#

// dotnet add package NATS.Net

// Create a new Key Value Store or get an existing one
ValueTask<INatsKVStore> CreateStoreAsync(string bucket, CancellationToken cancellationToken = default);

// Get a list of bucket names
IAsyncEnumerable<string> GetBucketNamesAsync(CancellationToken cancellationToken = default);

// Gets the status for all buckets
IAsyncEnumerable<NatsKVStatus> GetStatusesAsync(CancellationToken cancellationToken = default);

// Delete a Key Value Store
ValueTask<bool> DeleteStoreAsync(string bucket, CancellationToken cancellationToken = default);

//

C

NATS_EXTERN natsStatus 	kvConfig_Init (kvConfig *cfg)
 	Initializes a KeyValue configuration structure.
 
NATS_EXTERN natsStatus 	js_CreateKeyValue (kvStore **new_kv, jsCtx *js, kvConfig *cfg)
 	Creates a KeyValue store with a given configuration.
 
NATS_EXTERN natsStatus 	js_KeyValue (kvStore **new_kv, jsCtx *js, const char *bucket)
 	Looks-up and binds to an existing KeyValue store.
 
NATS_EXTERN natsStatus 	js_DeleteKeyValue (jsCtx *js, const char *bucket)
 	Deletes a KeyValue store.
 
NATS_EXTERN void 	kvStore_Destroy (kvStore *kv)
 	Destroys a KeyValue store object.

Getting

You can do a get to get the current value on a key, or ask to get a specific revision of the value.

Go

// Get returns the latest value for the key.
Get(key string) (entry KeyValueEntry, err error)
// GetRevision returns a specific revision value for the key.
GetRevision(key string, revision uint64) (entry KeyValueEntry, err error)

Java

/**
* Get the entry for a key
* @param key the key
* @return the KvEntry object or null if not found.
* @throws IOException covers various communication issues with the NATS
*         server such as timeout or interruption
* @throws JetStreamApiException the request had an error related to the data
* @throws IllegalArgumentException the server is not JetStream enabled
*/
KeyValueEntry get(String key) throws IOException, JetStreamApiException;

/**
* Get the specific revision of an entry for a key.
* @param key the key
* @param revision the revision
* @return the KvEntry object or null if not found.
* @throws IOException covers various communication issues with the NATS
*         server such as timeout or interruption
* @throws JetStreamApiException the request had an error related to the data
* @throws IllegalArgumentException the server is not JetStream enabled
*/
KeyValueEntry get(String key, long revision) throws IOException, JetStreamApiException;

JavaScript

async get(k: string): Promise<KvEntry | null>

Python

async def get(self, key: str) -> Entry:
   """
   get returns the latest value for the key.
   """

C#

// dotnet add package NATS.Net

// Get an entry from the bucket using the key
ValueTask<NatsKVEntry<T>> GetEntryAsync<T>(string key, ulong revision = default, INatsDeserialize<T>? serializer = default, CancellationToken cancellationToken = default);

//

C

NATS_EXTERN natsStatus 	kvStore_Get (kvEntry **new_entry, kvStore *kv, const char *key)
 	Returns the latest entry for the key.
 
NATS_EXTERN natsStatus 	kvStore_GetRevision (kvEntry **new_entry, kvStore *kv, const char *key, uint64_t revision)
 	Returns the entry at the specific revision for the key.

Putting

The key is always a string, you can simply use Put to store a byte array, or the convenience PutString to put a string. For 'compare and set' functionality you can use Create and Update.

Go

Put(key string, value []byte) (revision uint64, err error)
// PutString will place the string for the key into the store.
PutString(key string, value string) (revision uint64, err error)
// Create will add the key/value pair if it does not exist.
Create(key string, value []byte) (revision uint64, err error)
// Update will update the value if the latest revision matches.
Update(key string, value []byte, last uint64) (revision uint64, err error)

Java

/**
 * Put a byte[] as the value for a key
 * @param key the key
 * @param value the bytes of the value
 * @return the revision number for the key
 * @throws IOException covers various communication issues with the NATS
 *         server such as timeout or interruption
 * @throws JetStreamApiException the request had an error related to the data
 * @throws IllegalArgumentException the server is not JetStream enabled
 */
long put(String key, byte[] value) throws IOException, JetStreamApiException;

/**
 * Put a string as the value for a key
 * @param key the key
 * @param value the UTF-8 string
 * @return the revision number for the key
 * @throws IOException covers various communication issues with the NATS
 *         server such as timeout or interruption
 * @throws JetStreamApiException the request had an error related to the data
 * @throws IllegalArgumentException the server is not JetStream enabled
 */
long put(String key, String value) throws IOException, JetStreamApiException;

/**
 * Put a long as the value for a key
 * @param key the key
 * @param value the number
 * @return the revision number for the key
 * @throws IOException covers various communication issues with the NATS
 *         server such as timeout or interruption
 * @throws JetStreamApiException the request had an error related to the data
 * @throws IllegalArgumentException the server is not JetStream enabled
 */
long put(String key, Number value) throws IOException, JetStreamApiException;

/**
 * Put as the value for a key iff the key does not exist (there is no history)
 * or is deleted (history shows the key is deleted)
 * @param key the key
 * @param value the bytes of the value
 * @return the revision number for the key
 * @throws IOException covers various communication issues with the NATS
 *         server such as timeout or interruption
 * @throws JetStreamApiException the request had an error related to the data
 * @throws IllegalArgumentException the server is not JetStream enabled
 */
long create(String key, byte[] value) throws IOException, JetStreamApiException;

/**
 * Put as the value for a key iff the key exists and its last revision matches the expected
 * @param key the key
 * @param value the bytes of the value
 * @param expectedRevision the expected last revision
 * @return the revision number for the key
 * @throws IOException covers various communication issues with the NATS
 *         server such as timeout or interruption
 * @throws JetStreamApiException the request had an error related to the data
 * @throws IllegalArgumentException the server is not JetStream enabled
 */
long update(String key, byte[] value, long expectedRevision) throws IOException, JetStreamApiException;

JavaScript

  async put(
    k: string,
    data: Uint8Array,
    opts: Partial<KvPutOptions> = {},
  ): Promise<number>

create(k: string, data: Uint8Array): Promise<number>    
    
update(k: string, data: Uint8Array, version: number): Promise<number>

Python

async def put(self, key: str, value: bytes) -> int:
    """
    put will place the new value for the key into the store
    and return the revision number.
    """
    
async def update(self, key: str, value: bytes, last: int) -> int:
    """
    update will update the value iff the latest revision matches.
    """    

C#

// dotnet add package NATS.Net

// Put a value into the bucket using the key
// returns revision number
ValueTask<ulong> PutAsync<T>(string key, T value, INatsSerialize<T>? serializer = default, CancellationToken cancellationToken = default);

//

C

NATS_EXTERN natsStatus 	kvStore_Put (uint64_t *rev, kvStore *kv, const char *key, const void *data, int len)
 	Places the new value for the key into the store.
 
NATS_EXTERN natsStatus 	kvStore_PutString (uint64_t *rev, kvStore *kv, const char *key, const char *data)
 	Places the new value (as a string) for the key into the store.
 
NATS_EXTERN natsStatus 	kvStore_Create (uint64_t *rev, kvStore *kv, const char *key, const void *data, int len)
 	Places the value for the key into the store if and only if the key does not exist.
 
NATS_EXTERN natsStatus 	kvStore_CreateString (uint64_t *rev, kvStore *kv, const char *key, const char *data)
 	Places the value (as a string) for the key into the store if and only if the key does not exist.
 
NATS_EXTERN natsStatus 	kvStore_Update (uint64_t *rev, kvStore *kv, const char *key, const void *data, int len, uint64_t last)
 	Updates the value for the key into the store if and only if the latest revision matches.
 
NATS_EXTERN natsStatus 	kvStore_UpdateString (uint64_t *rev, kvStore *kv, const char *key, const char *data, uint64_t last)
 	Updates the value (as a string) for the key into the store if and only if the latest revision matches.

Deleting

You can delete a specific key, or purge the whole key/value bucket.

Go

// Delete will place a delete marker and leave all revisions.
Delete(key string) error
// Purge will place a delete marker and remove all previous revisions.
Purge(key string) error

Java

/**
* Soft deletes the key by placing a delete marker.
* @param key the key
* @throws IOException covers various communication issues with the NATS
*         server such as timeout or interruption
* @throws JetStreamApiException the request had an error related to the data
*/
void delete(String key) throws IOException, JetStreamApiException;

/**
* Purge all values/history from the specific key
* @param key the key
* @throws IOException covers various communication issues with the NATS
*         server such as timeout or interruption
* @throws JetStreamApiException the request had an error related to the data
*/
void purge(String key) throws IOException, JetStreamApiException;

JavaScript

delete(k: string): Promise<void>
    
purge(k: string): Promise<void>

Python

async def delete(self, key: str) -> bool:
    """
    delete will place a delete marker and remove all previous revisions.
    """
    
async def purge(self, key: str) -> bool:
    """
    purge will remove the key and all revisions.
    """    

C#

// dotnet add package NATS.Net

// Delete an entry from the bucket
ValueTask DeleteAsync(string key, NatsKVDeleteOpts? opts = default, CancellationToken cancellationToken = default);

// Purge an entry from the bucket
ValueTask PurgeAsync(string key, NatsKVDeleteOpts? opts = default, CancellationToken cancellationToken = default);

//

C

NATS_EXTERN natsStatus 	kvStore_Delete (kvStore *kv, const char *key)
 	Deletes a key by placing a delete marker and leaving all revisions.
 
NATS_EXTERN natsStatus 	kvStore_Purge (kvStore *kv, const char *key, kvPurgeOptions *opts)
 	Deletes a key by placing a purge marker and removing all revisions.
 	
NATS_EXTERN natsStatus 	kvStore_PurgeDeletes (kvStore *kv, kvPurgeOptions *opts)
 	Purge and removes delete markers.

Getting all the keys

You can get the list of all the keys currently having a value associated using Keys()

Go

// Keys will return all keys.
Keys(opts ...WatchOpt) ([]string, error)

Java

/**
 * Get a list of the keys in a bucket.
 * @return List of keys
 * @throws IOException covers various communication issues with the NATS
 *         server such as timeout or interruption
 * @throws JetStreamApiException the request had an error related to the data
 * @throws InterruptedException if the thread is interrupted
 */
List<String> keys() throws IOException, JetStreamApiException, InterruptedException;

JavaScript

async keys(k = ">"): Promise<QueuedIterator<string>>

C#

// dotnet add package NATS.Net

// Get all the keys in the bucket
IAsyncEnumerable<string> GetKeysAsync(NatsKVWatchOpts? opts = default, CancellationToken cancellationToken = default);

// Get a filtered set of keys in the bucket
IAsyncEnumerable<string> GetKeysAsync(IEnumerable<string> filters, NatsKVWatchOpts? opts = default, CancellationToken cancellationToken = default);

//

C

NATS_EXTERN natsStatus 	kvStore_Keys (kvKeysList *list, kvStore *kv, kvWatchOptions *opts)
 	Returns all keys in the bucket.
 
NATS_EXTERN void 	kvKeysList_Destroy (kvKeysList *list)
 	Destroys this list of KeyValue store key strings.

Getting the history for a key

The JetStream key/value store has a feature you don't usually find in key/value stores: the ability to keep a history of the values associated with a key (rather than just the current value). The depth of the history is specified when the key/value bucket is created, and the default is a history depth of 1 (i.e. no history).

Go

// History will return all historical values for the key.
History(key string, opts ...WatchOpt) ([]KeyValueEntry, error)

Java

/**
 * Get the history (list of KeyValueEntry) for a key
 * @param key the key
 * @return List of KvEntry
 * @throws IOException covers various communication issues with the NATS
 *         server such as timeout or interruption
 * @throws JetStreamApiException the request had an error related to the data
 * @throws InterruptedException if the thread is interrupted
 */
List<KeyValueEntry> history(String key) throws IOException, JetStreamApiException, InterruptedException;

JavaScript

async history(
    opts: { key?: string; headers_only?: boolean } = {},
  ): Promise<QueuedIterator<KvEntry>>

C#

// dotnet add package NATS.Net

// Get the history of an entry by key
IAsyncEnumerable<NatsKVEntry<T>> HistoryAsync<T>(string key, INatsDeserialize<T>? serializer = default, NatsKVWatchOpts? opts = default, CancellationToken cancellationToken = default);

//

C

NATS_EXTERN natsStatus 	kvStore_History (kvEntryList *list, kvStore *kv, const char *key, kvWatchOptions *opts)
 	Returns all historical entries for the key.
 
NATS_EXTERN void 	kvEntryList_Destroy (kvEntryList *list)
 	Destroys this list of KeyValue store entries.

Watching for changes

Watching a key/value bucket is like subscribing to updates: you provide a callback and you can watch all of the keys in the bucket or specify which specific key(s) you want to be kept updated about.

Go

// Watch for any updates to keys that match the keys argument which could include wildcards.
// Watch will send a nil entry when it has received all initial values.
Watch(keys string, opts ...WatchOpt) (KeyWatcher, error)
// WatchAll will invoke the callback for all updates.
WatchAll(opts ...WatchOpt) (KeyWatcher, error)

Java

/**
 * Watch updates for a specific key
 */
NatsKeyValueWatchSubscription watch(String key, KeyValueWatcher watcher, KeyValueWatchOption... watchOptions) throws IOException, JetStreamApiException, InterruptedException;

/**
 * Watch updates for all keys
 */
NatsKeyValueWatchSubscription watchAll(KeyValueWatcher watcher, KeyValueWatchOption... watchOptions) throws IOException, JetStreamApiException, InterruptedException;

JavaScript

  async watch(
    opts: {
      key?: string;
      headers_only?: boolean;
      initializedFn?: callbackFn;
    } = {},
  ): Promise<QueuedIterator<KvEntry>>

C#

// dotnet add package NATS.Net

// Start a watcher for specific keys
// Key to watch is subject-based and wildcards may be used
IAsyncEnumerable<NatsKVEntry<T>> WatchAsync<T>(string key, INatsDeserialize<T>? serializer = default, NatsKVWatchOpts? opts = default, CancellationToken cancellationToken = default);

// Start a watcher for specific keys
// Key to watch are subject-based and wildcards may be used
IAsyncEnumerable<NatsKVEntry<T>> WatchAsync<T>(IEnumerable<string> keys, INatsDeserialize<T>? serializer = default, NatsKVWatchOpts? opts = default, CancellationToken cancellationToken = default);

// Start a watcher for all the keys in the bucket
IAsyncEnumerable<NatsKVEntry<T>> WatchAsync<T>(INatsDeserialize<T>? serializer = default, NatsKVWatchOpts? opts = default, CancellationToken cancellationToken = default);

//

C

NATS_EXTERN natsStatus 	kvStore_Watch (kvWatcher **new_watcher, kvStore *kv, const char *keys, kvWatchOptions *opts)
 	Returns a watcher for any updates to keys that match the keys argument.
 
NATS_EXTERN natsStatus 	kvStore_WatchAll (kvWatcher **new_watcher, kvStore *kv, kvWatchOptions *opts)
 	Returns a watcher for any updates to any keys of the KeyValue store bucket.