State

You can store key-value state in Restate. Restate makes sure the state is consistent with the processing of the code execution.

This feature is only available for Virtual Objects and Workflows:

• For Virtual Objects, the state is isolated per Virtual Object and lives forever (across invocations for that object).
• For Workflows, you can think of it as if every workflow execution is a new object. So the state is isolated to a single workflow execution. The state can only be mutated by the run handler of the workflow. The other handlers can only read the state.

Command-line introspection

You can inspect and edit the K/V state stored in Restate via psql and the CLI. Have a look at the introspection docs for more information.

You can do the following operations on the state:

Java

Kotlin

Listing state keys

For a single Virtual Object, you can list all the state keys that have entries in the state store via:

Java

Collection<String> keys = ctx.stateKeys();

Kotlin

val keys = ctx.stateKeys()

Retrieving state

Java

// Getting String value
StateKey<String> STRING_STATE_KEY = StateKey.of("my-key", JsonSerdes.STRING);
String stringState = ctx.get(STRING_STATE_KEY).orElse("my-default");

// Getting integer value
StateKey<Integer> INT_STATE_KEY = StateKey.of("my-key", JsonSerdes.INT);
int intState = ctx.get(INT_STATE_KEY).orElse(0);

1. Define the state key (key name and (de)serializer) at the top of the Virtual Object class.
2. Use ctx.get to retrieve the state for a specific key.

Kotlin

// Getting String value
val STRING_STATE_KEY = KtStateKey.json<String>("my-key")
val stringState: String? = ctx.get(STRING_STATE_KEY)

// Getting integer value
val INT_STATE_KEY = KtStateKey.json<Int>("my-key")
val intState: Int? = ctx.get(INT_STATE_KEY)

1. Define the state key (key name and (de)serializer) at the top of the Virtual Object class.
2. Use ctx.get to retrieve the state for a specific key.

Setting state

Java

StateKey<String> STRING_STATE_KEY = StateKey.of("my-key", JsonSerdes.STRING);
ctx.set(STRING_STATE_KEY, "my-new-value");

1. Define the state key (key name and (de)serializer) at the top of the Virtual Object class.
2. Use ctx.set to set the state for a specific key. The type of value needs to line up with the type that was defined in the StateKey.

Kotlin

val STRING_STATE_KEY = KtStateKey.json<String>("my-key")
ctx.set(STRING_STATE_KEY, "my-new-value")

1. Define the state key (key name and (de)serializer) at the top of the Virtual Object class.
2. Use ctx.set to set the state for a specific key. The type of value needs to line up with the type that was defined in the StateKey.

Clearing state

Java

StateKey<String> STRING_STATE_KEY = StateKey.of("my-key", JsonSerdes.STRING);
ctx.clear(STRING_STATE_KEY);

1. Define the state key (key name and (de)serializer) at the top of the Virtual Object class.
2. Use ctx.clear to delete the state for a specific key.

Kotlin

val STRING_STATE_KEY = KtStateKey.json<String>("my-key")
ctx.clear(STRING_STATE_KEY)

1. Define the state key (key name and (de)serializer) at the top of the Virtual Object class.
2. Use ctx.clear to delete the state for a specific key.

Clearing all state

Java

ctx.clearAll();

Kotlin

ctx.clearAll()

This will delete all the state stored in Restate for the Virtual Object.