The SpacetimeDB Rust client SDK

The SpacetimeDB client SDK for Rust contains all the tools you need to build native clients for SpacetimeDB modules using Rust.

Name	Description
Project setup	Configure a Rust crate to use the SpacetimeDB Rust client SDK.
Generate module bindings	Use the SpacetimeDB CLI to generate module-specific types and interfaces.
DbConnection type	A connection to a remote database.
DbContext trait	Methods for interacting with the remote database. Implemented by DbConnection and various event context types.
EventContext type	DbContext available in row callbacks.
ReducerEventContext type	DbContext available in reducer callbacks.
SubscriptionEventContext type	DbContext available in subscription-related callbacks.
ErrorContext type	DbContext available in error-related callbacks.
Access the client cache	Make local queries against subscribed rows, and register row callbacks to run when subscribed rows change.
Observe and invoke reducers	Send requests to the database to run reducers, and register callbacks to run when notified of reducers.
Identify a client	Types for identifying users and client connections.

Project setup

First, create a new project using cargo new and add the SpacetimeDB SDK to your dependencies:

cargo add spacetimedb_sdk

Generate module bindings

Each SpacetimeDB client depends on some bindings specific to your module. Create a module_bindings directory in your project's src directory and generate the Rust interface files using the Spacetime CLI. From your project directory, run:

mkdir -p src/module_bindings
spacetime generate --lang rust \
    --out-dir src/module_bindings \
    --project-path PATH-TO-MODULE-DIRECTORY

Replace PATH-TO-MODULE-DIRECTORY with the path to your SpacetimeDB module.

Declare a mod for the bindings in your client's src/main.rs:

mod module_bindings;

Type DbConnection

module_bindings::DbConnection

A connection to a remote database is represented by the module_bindings::DbConnection type. This type is generated per-module, and contains information about the types, tables and reducers defined by your module.

Name	Description
Connect to a database	Construct a DbConnection.
Advance the connection	Poll the DbConnection, or set up a background worker to run it.
Access tables and reducers	Access subscribed rows in the client cache, request reducer invocations, and register callbacks.

Connect to a database

impl DbConnection {
    fn builder() -> DbConnectionBuilder;
}

Construct a DbConnection by calling DbConnection::builder() and chaining configuration methods, then calling .build(). You must at least specify with_uri, to supply the URI of the SpacetimeDB to which you published your module, and with_module_name, to supply the human-readable SpacetimeDB domain name or the raw Identity which identifies the database.

Name	Description
with_uri method	Set the URI of the SpacetimeDB instance which hosts the remote database.
with_module_name method	Set the name or Identity of the remote database.
on_connect callback	Register a callback to run when the connection is successfully established.
on_connect_error callback	Register a callback to run if the connection is rejected or the host is unreachable.
on_disconnect callback	Register a callback to run when the connection ends.
with_token method	Supply a token to authenticate with the remote database.
build method	Finalize configuration and connect.

Method with_uri

impl DbConnectionBuilder {
    fn with_uri(self, uri: impl TryInto<Uri>) -> Self;
}

Configure the URI of the SpacetimeDB instance or cluster which hosts the remote database containing the module.

Method with_module_name

impl DbConnectionBuilder {
    fn with_module_name(self, name_or_identity: impl ToString) -> Self;
}

Configure the SpacetimeDB domain name or Identity of the remote database which identifies it within the SpacetimeDB instance or cluster.

Callback on_connect

impl DbConnectionBuilder {
    fn on_connect(self, callback: impl FnOnce(&DbConnection, Identity, &str)) -> DbConnectionBuilder;
}

Chain a call to .on_connect(callback) to your builder to register a callback to run when your new DbConnection successfully initiates its connection to the remote database. The callback accepts three arguments: a reference to the DbConnection, the Identity by which SpacetimeDB identifies this connection, and a private access token which can be saved and later passed to with_token to authenticate the same user in future connections.

This interface may change in an upcoming release as we rework SpacetimeDB's authentication model.

Callback on_connect_error

impl DbConnectionBuilder {
    fn on_connect_error(
        self,
        callback: impl FnOnce(&ErrorContext, spacetimedb_sdk::Error),
    ) -> DbConnectionBuilder;
}

Chain a call to .on_connect_error(callback) to your builder to register a callback to run when your connection fails.

A known bug in the SpacetimeDB Rust client SDK currently causes this callback never to be invoked. on_disconnect callbacks are invoked instead.

Callback on_disconnect

impl DbConnectionBuilder {
    fn on_disconnect(
        self,
        callback: impl FnOnce(&ErrorContext, Option<spacetimedb_sdk::Error>),
    ) -> DbConnectionBuilder;
}

Chain a call to .on_disconnect(callback) to your builder to register a callback to run when your DbConnection disconnects from the remote database, either as a result of a call to disconnect or due to an error.

Method with_token

impl DbConnectionBuilder {
    fn with_token(self, token: Option<impl ToString>>) -> Self;
}

Chain a call to .with_token(token) to your builder to provide an OpenID Connect compliant JSON Web Token to authenticate with, or to explicitly select an anonymous connection. If this method is not called or None is passed, SpacetimeDB will generate a new Identity and sign a new private access token for the connection.

Method build

impl DbConnectionBuilder {
    fn build(self) -> Result<DbConnection, spacetimedb_sdk::Error>;
}

After configuring the connection and registering callbacks, attempt to open the connection.

Advance the connection and process messages

In the interest of supporting a wide variety of client applications with different execution strategies, the SpacetimeDB SDK allows you to choose when the DbConnection spends compute time and processes messages. If you do not arrange for the connection to advance by calling one of these methods, the DbConnection will never advance, and no callbacks will ever be invoked.

Name	Description
run_threaded method	Spawn a thread to process messages in the background.
run_async method	Process messages in an async task.
frame_tick method	Process messages on the main thread without blocking.

Method run_threaded

impl DbConnection {
    fn run_threaded(&self) -> std::thread::JoinHandle<()>;
}

run_threaded spawns a thread which will continuously advance the connection, sleeping when there is no work to do. The thread will panic if the connection disconnects erroneously, or return if it disconnects as a result of a call to disconnect.

Method run_async

impl DbConnection {
    async fn run_async(&self) -> Result<(), spacetimedb_sdk::Error>;
}

run_async will continuously advance the connection, await-ing when there is no work to do. The task will return an Err if the connection disconnects erroneously, or return Ok(()) if it disconnects as a result of a call to disconnect.

Method frame_tick

impl DbConnection {
    fn frame_tick(&self) -> Result<(), spacetimedb_sdk::Error>;
}

frame_tick will advance the connection until no work remains, then return rather than blocking or await-ing. Games might arrange for this message to be called every frame. frame_tick returns Ok if the connection remains active afterwards, or Err if the connection disconnected before or during the call.

Access tables and reducers

Field db

struct DbConnection {
    pub db: RemoteTables,
    /* other members */
}

The db field of the DbConnection provides access to the subscribed view of the remote database's tables. See Access the client cache.

Field reducers

struct DbConnection {
    pub reducers: RemoteReducers,
    /* other members */
}

The reducers field of the DbConnection provides access to reducers exposed by the remote module. See Observe and invoke reducers.

Trait DbContext

trait spacetimedb_sdk::DbContext {
    /* methods */
}

DbConnection, EventContext, ReducerEventContext, SubscriptionEventContext and ErrorContext all implement DbContext. DbContext has methods for inspecting and configuring your connection to the remote database, including ctx.db(), a trait-generic alternative to reading the .db property on a concrete-typed context object.

The DbContext trait is implemented by connections and contexts to every module. This means that its DbView and Reducers are associated types.

Name	Description
RemoteDbContext trait	Module-specific DbContext extension trait with associated types bound.
db method	Trait-generic alternative to the db field of DbConnection.
reducers method	Trait-generic alternative to the reducers field of DbConnection.
disconnect method	End the connection.
Subscribe to queries	Register SQL queries to receive updates about matching rows.
Read connection metadata	Access the connection's Identity and ConnectionId

Trait RemoteDbContext

trait module_bindings::RemoteDbContext
    : spacetimedb_sdk::DbContext</* Associated type constraints */> {}

Each module's module_bindings exports a trait RemoteDbContext which extends DbContext, with the associated types DbView and Reducers bound to the types defined for that module. This can be more convenient when creating functions that can be called from any callback for a specific module, but which access the database or invoke reducers, and so must know the type of the DbView or Reducers.

Method db

trait DbContext {
    fn db(&self) -> &Self::DbView;
}

When operating in trait-generic contexts, it is necessary to call the ctx.db() method, rather than accessing the ctx.db field, as Rust traits cannot expose fields.

Example

fn print_users(ctx: &impl RemoteDbContext) {
    for user in ctx.db().user().iter() {
        println!("{}", user.name);
    }
}

Method reducers

trait DbContext {
    fn reducerrs(&self) -> &Self::Reducers;
}

When operating in trait-generic contexts, it is necessary to call the ctx.reducers() method, rather than accessing the ctx.reducers field, as Rust traits cannot expose fields.

Example

fn call_say_hello(ctx: &impl RemoteDbContext) {
    ctx.reducers.say_hello();
}

Method disconnect

trait DbContext {
    fn disconnect(&self) -> spacetimedb_sdk::Result<()>;
}

Gracefully close the DbConnection. Returns an Err if the connection is already disconnected.

Subscribe to queries

Name	Description
SubscriptionBuilder type	Builder-pattern constructor to register subscribed queries.
SubscriptionHandle type	Manage an active subscripion.

Type SubscriptionBuilder

spacetimedb_sdk::SubscriptionBuilder

Name	Description
ctx.subscription_builder() constructor	Begin configuring a new subscription.
on_applied callback	Register a callback to run when matching rows become available.
on_error callback	Register a callback to run if the subscription fails.
subscribe method	Finish configuration and subscribe to one or more SQL queries.
subscribe_to_all_tables method	Convenience method to subscribe to the entire database.

Constructor ctx.subscription_builder()

trait DbContext {
    fn subscription_builder(&self) -> SubscriptionBuilder;
}

Subscribe to queries by calling ctx.subscription_builder() and chaining configuration methods, then calling .subscribe(queries).

Callback on_applied

impl SubscriptionBuilder {
    fn on_applied(self, callback: impl FnOnce(&SubscriptionEventContext)) -> Self;
}

Register a callback to run when the subscription is applied and the matching rows are inserted into the client cache.

Callback on_error

impl SubscriptionBuilder {
    fn on_error(self, callback: impl FnOnce(&ErrorContext, spacetimedb_sdk::Error)) -> Self;
}

Register a callback to run if the subscription is rejected or unexpectedly terminated by the server. This is most frequently caused by passing an invalid query to subscribe.

Method subscribe

impl SubscriptionBuilder {
    fn subscribe(self, queries: impl IntoQueries) -> SubscriptionHandle;
}

Subscribe to a set of queries. queries should be a string or an array, vec or slice of strings.

See the SpacetimeDB SQL Reference for information on the queries SpacetimeDB supports as subscriptions.

Method subscribe_to_all_tables

impl SubscriptionBuilder {
    fn subscribe_to_all_tables(self);
}

Subscribe to all rows from all public tables. This method is provided as a convenience for simple clients. The subscription initiated by subscribe_to_all_tables cannot be canceled after it is initiated. You should subscribe to specific queries if you need fine-grained control over the lifecycle of your subscriptions.

Type SubscriptionHandle

module_bindings::SubscriptionHandle

A SubscriptionHandle represents a subscribed query or a group of subscribed queries.

The SubscriptionHandle does not contain or provide access to the subscribed rows. Subscribed rows of all subscriptions by a connection are contained within that connection's ctx.db. See Access the client cache.

Name	Description
is_ended method	Determine whether the subscription has ended.
is_active method	Determine whether the subscription is active and its matching rows are present in the client cache.
unsubscribe method	Discard a subscription.
unsubscribe_then method	Discard a subscription, and register a callback to run when its matching rows are removed from the client cache.

Method is_ended

impl SubscriptionHandle {
    fn is_ended(&self) -> bool;
}

Returns true if this subscription has been terminated due to an unsubscribe call or an error.

Method is_active

impl SubscriptionHandle {
    fn is_active(&self) -> bool;
}

Returns true if this subscription has been applied and has not yet been unsubscribed.

Method unsubscribe

impl SubscriptionHandle {
    fn unsubscribe(&self) -> Result<(), spacetimedb_sdk::Error>;
}

Terminate this subscription, causing matching rows to be removed from the client cache. Any rows removed from the client cache this way will have on_delete callbacks run for them.

Unsubscribing is an asynchronous operation. Matching rows are not removed from the client cache immediately. Use unsubscribe_then to run a callback once the unsubscribe operation is completed.

Returns an error if the subscription has already ended, either due to a previous call to unsubscribe or unsubscribe_then, or due to an error.

Method unsubscribe_then

impl SubscriptionHandle {
    fn unsubscribe_then(
        self,
        on_end: impl FnOnce(&SubscriptionEventContext),
    ) -> Result<(), spacetimedb_sdk::Error>;
}

Terminate this subscription, and run the on_end callback when the subscription is ended and its matching rows are removed from the client cache. Any rows removed from the client cache this way will have on_delete callbacks run for them.

Returns an error if the subscription has already ended, either due to a previous call to unsubscribe or unsubscribe_then, or due to an error.

Read connection metadata

Method identity

trait DbContext {
    fn identity(&self) -> Identity;
}

Get the Identity with which SpacetimeDB identifies the connection. This method may panic if the connection was initiated anonymously and the newly-generated Identity has not yet been received, i.e. if called before the on_connect callback is invoked.

Method try_identity

trait DbContext {
    fn try_identity(&self) -> Option<Identity>;
}

Like DbContext::identity, but returns None instead of panicking if the Identity is not yet available.

Method connection_id

trait DbContext {
    fn connection_id(&self) -> ConnectionId;
}

Get the ConnectionId with which SpacetimeDB identifies the connection.

Method is_active

trait DbContext {
    fn is_active(&self) -> bool;
}

true if the connection has not yet disconnected. Note that a connection is_active when it is constructed, before its on_connect callback is invoked.

Type EventContext

module_bindings::EventContext

An EventContext is a DbContext augmented with a field event: Event. EventContexts are passed as the first argument to row callbacks on_insert, on_delete and on_update.

Name	Description
event field	Enum describing the cause of the current row callback.
db field	Provides access to the client cache.
reducers field	Allows requesting reducers run on the remote database.
Event enum	Possible events which can cause a row callback to be invoked.

Field event

struct EventContext {
    pub event: spacetimedb_sdk::Event<module_bindings::Reducer>,
    /* other fields */
}

The Event contained in the EventContext describes what happened to cause the current row callback to be invoked.

Field db

struct EventContext {
    pub db: RemoteTables,
    /* other members */
}

The db field of the context provides access to the subscribed view of the remote database's tables. See Access the client cache.

Field reducers

struct EventContext {
    pub reducers: RemoteReducers,
    /* other members */
}

The reducers field of the context provides access to reducers exposed by the remote module. See Observe and invoke reducers.

Enum Event

spacetimedb_sdk::Event<module_bindings::Reducer>

Name	Description
Reducer variant	A reducer ran in the remote database.
SubscribeApplied variant	A new subscription was applied to the client cache.
UnsubscribeApplied variant	A previous subscription was removed from the client cache after a call to unsubscribe.
SubscribeError variant	A previous subscription was removed from the client cache due to an error.
UnknownTransaction variant	A transaction ran in the remote database, but was not attributed to a known reducer.
ReducerEvent struct	Metadata about a reducer run. Contained in Event::Reducer and ReducerEventContext.
Status enum	Completion status of a reducer run.
Reducer enum	Module-specific generated enum with a variant for each reducer defined by the module.

Variant Reducer

spacetimedb_sdk::Event::Reducer(spacetimedb_sdk::ReducerEvent<module_bindings::Reducer>)

Event when we are notified that a reducer ran in the remote database. The ReducerEvent contains metadata about the reducer run, including its arguments and termination Status.

This event is passed to row callbacks resulting from modifications by the reducer.

Variant SubscribeApplied

spacetimedb_sdk::Event::SubscribeApplied

Event when our subscription is applied and its rows are inserted into the client cache.

This event is passed to row on_insert callbacks resulting from the new subscription.

Variant UnsubscribeApplied

spacetimedb_sdk::Event::UnsubscribeApplied

Event when our subscription is removed after a call to SubscriptionHandle::unsubscribe or SubscriptionHandle::unsubscribe_then and its matching rows are deleted from the client cache.

This event is passed to row on_delete callbacks resulting from the subscription ending.

Variant SubscribeError

spacetimedb_sdk::Event::SubscribeError(spacetimedb_sdk::Error)

Event when a subscription ends unexpectedly due to an error.

This event is passed to row on_delete callbacks resulting from the subscription ending.

Variant UnknownTransaction

Event when we are notified of a transaction in the remote database which we cannot associate with a known reducer. This may be an ad-hoc SQL query or a reducer for which we do not have bindings.

This event is passed to row callbacks resulting from modifications by the transaction.

Struct ReducerEvent

spacetimedb_sdk::ReducerEvent<module_bindings::Reducer>

A ReducerEvent contains metadata about a reducer run.

struct spacetimedb_sdk::ReducerEvent<R> {
    /// The time at which the reducer was invoked.
    timestamp: SystemTime,

    /// Whether the reducer committed, was aborted due to insufficient energy, or failed with an error message.
    status: Status,

    /// The `Identity` of the SpacetimeDB actor which invoked the reducer.
    caller_identity: Identity,

    /// The `ConnectionId` of the SpacetimeDB actor which invoked the reducer,
    /// or `None` for scheduled reducers.
    caller_connection_id: Option<ConnectionId>,

    /// The amount of energy consumed by the reducer run, in eV.
    /// (Not literal eV, but our SpacetimeDB energy unit eV.)
    ///
    /// May be `None` if the module is configured not to broadcast energy consumed.
    energy_consumed: Option<u128>,

    /// The `Reducer` enum defined by the `module_bindings`, which encodes which reducer ran and its arguments.
    reducer: R,

    // ...private fields
}

Enum Status

spacetimedb_sdk::Status

Name	Description
Committed variant	The reducer ran successfully.
Failed variant	The reducer errored.
OutOfEnergy variant	The reducer was aborted due to insufficient energy.

Variant Committed

spacetimedb_sdk::Status::Committed

The reducer returned successfully and its changes were committed into the database state. An Event::Reducer passed to a row callback must have this status in its ReducerEvent.

Variant Failed

spacetimedb_sdk::Status::Failed(Box<str>)

The reducer returned an error, panicked, or threw an exception. The enum payload is the stringified error message. Formatting of the error message is unstable and subject to change, so clients should use it only as a human-readable diagnostic, and in particular should not attempt to parse the message.

Variant OutOfEnergy

The reducer was aborted due to insufficient energy balance of the module owner.

Enum Reducer

module_bindings::Reducer

The module bindings contains an enum Reducer with a variant for each reducer defined by the module. Each variant has a payload containing the arguments to the reducer.

Type ReducerEventContext

A ReducerEventContext is a DbContext augmented with a field event: ReducerEvent. ReducerEventContexts are passed as the first argument to reducer callbacks.

Name	Description
event field	ReducerEvent containing reducer metadata.
db field	Provides access to the client cache.
reducers field	Allows requesting reducers run on the remote database.

Field event

struct ReducerEventContext {
    pub event: spacetimedb_sdk::ReducerEvent<module_bindings::Reducer>,
    /* other fields */
}

The ReducerEvent contained in the ReducerEventContext has metadata about the reducer which ran.

Field db

struct ReducerEventContext {
    pub db: RemoteTables,
    /* other members */
}

The db field of the context provides access to the subscribed view of the remote database's tables. See Access the client cache.

Field reducers

struct ReducerEventContext {
    pub reducers: RemoteReducers,
    /* other members */
}

The reducers field of the context provides access to reducers exposed by the remote module. See Observe and invoke reducers.

Type SubscriptionEventContext

A SubscriptionEventContext is a DbContext. Unlike the other context types, SubscriptionEventContext doesn't have an event field. SubscriptionEventContexts are passed to subscription on_applied and unsubscribe_then callbacks.

Name	Description
db field	Provides access to the client cache.
reducers field	Allows requesting reducers run on the remote database.

Field db

struct SubscriptionEventContext {
    pub db: RemoteTables,
    /* other members */
}

The db field of the context provides access to the subscribed view of the remote database's tables. See Access the client cache.

Field reducers

struct SubscriptionEventContext {
    pub reducers: RemoteReducers,
    /* other members */
}

The reducers field of the context provides access to reducers exposed by the remote module. See Observe and invoke reducers.

Type ErrorContext

An ErrorContext is a DbContext augmented with a field event: spacetimedb_sdk::Error. ErrorContexts are to connections' on_disconnect and on_connect_error callbacks, and to subscriptions' on_error callbacks.

Name	Description
event field	The error which caused the current error callback.
db field	Provides access to the client cache.
reducers field	Allows requesting reducers run on the remote database.

Field event

struct ErrorContext {
    pub event: spacetimedb_sdk::Error,
    /* other fields */
}

Field db

struct ErrorContext {
    pub db: RemoteTables,
    /* other members */
}

The db field of the context provides access to the subscribed view of the remote database's tables. See Access the client cache.

Field reducers

struct ErrorContext {
    pub reducers: RemoteReducers,
    /* other members */
}

The reducers field of the context provides access to reducers exposed by the remote module. See Observe and invoke reducers.

Access the client cache

All DbContext implementors, including DbConnection and EventContext, have fields .db, which in turn has methods for accessing tables in the client cache. The trait method DbContext::db(&self) can also be used in contexts with an impl DbContext rather than a concrete-typed EventContext or DbConnection.

Each table defined by a module has an accessor method, whose name is the table name converted to snake_case, on this .db field. The methods are defined via extension traits, which rustc or your IDE should help you identify and import where necessary. The table accessor methods return table handles, which implement Table, may implement TableWithPrimaryKey, and have methods for searching by unique index.

Name	Description
Table trait	Provides access to subscribed rows of a specific table within the client cache.
TableWithPrimaryKey trait	Extension trait for tables which have a column designated as a primary key.
Unique constraint index access	Seek a subscribed row by the value in its unique or primary key column.
BTree index access	Not supported.

Trait Table

spacetimedb_sdk::Table

Implemented by all table handles.

Name	Description
Row associated type	The type of rows in the table.
count method	The number of subscribed rows in the table.
iter method	Iterate over all subscribed rows in the table.
on_insert callback	Register a callback to run whenever a row is inserted into the client cache.
on_delete callback	Register a callback to run whenever a row is deleted from the client cache.

Associated type Row

trait spacetimedb_sdk::Table {
    type Table::Row;
}

The type of rows in the table.

Method count

trait spacetimedb_sdk::Table {
    fn count(&self) -> u64;
}

Returns the number of rows of this table resident in the client cache, i.e. the total number which match any subscribed query.

Method iter

trait spacetimedb_sdk::Table {
    fn iter(&self) -> impl Iterator<Item = Self::Row>;
}

An iterator over all the subscribed rows in the client cache, i.e. those which match any subscribed query.

Callback on_insert

trait spacetimedb_sdk::Table {
    type InsertCallbackId;

    fn on_insert(&self, callback: impl FnMut(&EventContext, &Self::Row)) -> Self::InsertCallbackId;

    fn remove_on_insert(&self, callback: Self::InsertCallbackId);
}

The on_insert callback runs whenever a new row is inserted into the client cache, either when applying a subscription or being notified of a transaction. The passed EventContext contains an Event which can identify the change which caused the insertion, and also allows the callback to interact with the connection, inspect the client cache and invoke reducers.

Registering an on_insert callback returns a callback id, which can later be passed to remove_on_insert to cancel the callback. Newly registered or canceled callbacks do not take effect until the following event.

Callback on_delete

trait spacetimedb_sdk::Table {
    type DeleteCallbackId;

    fn on_delete(&self, callback: impl FnMut(&EventContext, &Self::Row)) -> Self::DeleteCallbackId;

    fn remove_on_delete(&self, callback: Self::DeleteCallbackId);
}

The on_delete callback runs whenever a previously-resident row is deleted from the client cache. Registering an on_delete callback returns a callback id, which can later be passed to remove_on_delete to cancel the callback. Newly registered or canceled callbacks do not take effect until the following event.

Trait TableWithPrimaryKey

spacetimedb_sdk::TableWithPrimaryKey

Implemented for table handles whose tables have a primary key.

Name	Description
on_update callback	Register a callback to run whenever a subscribed row is replaced with a new version.

Callback on_update

trait spacetimedb_sdk::TableWithPrimaryKey {
    type UpdateCallbackId;

    fn on_update(&self, callback: impl FnMut(&EventContext, &Self::Row, &Self::Row)) -> Self::UpdateCallbackId;

    fn remove_on_update(&self, callback: Self::UpdateCallbackId);
}

The on_update callback runs whenever an already-resident row in the client cache is updated, i.e. replaced with a new row that has the same primary key. Registering an on_update callback returns a callback id, which can later be passed to remove_on_update to cancel the callback. Newly registered or canceled callbacks do not take effect until the following event.

Unique constraint index access

For each unique constraint on a table, its table handle has a method whose name is the unique column name which returns a unique index handle. The unique index handle has a method .find(desired_val: &Col) -> Option<Row>, where Col is the type of the column, and Row the type of rows. If a row with desired_val in the unique column is resident in the client cache, .find returns it.

BTree index access

The SpacetimeDB Rust client SDK does not support non-unique BTree indexes.

Observe and invoke reducers

All DbContext implementors, including DbConnection and EventContext, have fields .reducers, which in turn has methods for invoking reducers defined by the module and registering callbacks on it. The trait method DbContext::reducers(&self) can also be used in contexts with an impl DbContext rather than a concrete-typed EventContext or DbConnection.

Each reducer defined by the module has three methods on the .reducers:

• An invoke method, whose name is the reducer's name converted to snake case, like set_name. This requests that the module run the reducer.
• A callback registation method, whose name is prefixed with on_, like on_set_name. This registers a callback to run whenever we are notified that the reducer ran, including successfully committed runs and runs we requested which failed. This method returns a callback id, which can be passed to the callback remove method.
• A callback remove method, whose name is prefixed with remove_on_, like remove_on_set_name. This cancels a callback previously registered via the callback registration method.

Identify a client

Type Identity

spacetimedb_sdk::Identity

A unique public identifier for a client connected to a database.

Type ConnectionId

spacetimedb_sdk::ConnectionId

An opaque identifier for a client connection to a database, intended to differentiate between connections from the same Identity.