SpacetimeDB Unreal Engine Integration

This skill covers Unreal Engine-specific patterns for connecting to SpacetimeDB. For server-side module development, see the

rust-server

csharp-server

skills.

Installation

Add the SpacetimeDB Unreal SDK as a plugin:

Create a
```
Plugins
```
folder in your Unreal project root if it does not exist.
Copy the
```
SpacetimeDbSdk
```
folder into
```
Plugins/
```
.
Right-click your
```
.uproject
```
file and select Generate Visual Studio project files.
Add
```
"SpacetimeDbSdk"
```
to your module's
```
Build.cs
```
:

csharp

PublicDependencyModuleNames.AddRange(new string[] { "SpacetimeDbSdk" });

Generate Module Bindings

bash

spacetime generate --lang unrealcpp \
  --uproject-dir <path_to_uproject_directory> \
  --module-path <path_to_spacetimedb_module> \
  --unreal-module-name <your_unreal_module_name>

This generates C++ bindings in

ModuleBindings/

inside your project. Include the generated header:

cpp

#include "ModuleBindings/SpacetimeDBClient.g.h"

Regenerate whenever you change module tables, reducers, or types.

GameManager Actor Pattern

The recommended pattern is a singleton Actor that owns the connection. Enable ticking so

FrameTick

is called every frame.

Header (GameManager.h)

cpp

#pragma once
#include "CoreMinimal.h"
#include "GameFramework/Actor.h"
#include "ModuleBindings/SpacetimeDBClient.g.h"
#include "GameManager.generated.h"

class UDbConnection;

UCLASS()
class AGameManager : public AActor
{
    GENERATED_BODY()
public:
    AGameManager();
    static AGameManager* Instance;

    UPROPERTY(EditAnywhere, Category="SpacetimeDB")
    FString ServerUri = TEXT("127.0.0.1:3000");

    UPROPERTY(EditAnywhere, Category="SpacetimeDB")
    FString DatabaseName = TEXT("my-module");

    UPROPERTY(BlueprintReadOnly, Category="SpacetimeDB")
    UDbConnection* Conn = nullptr;

    UPROPERTY(BlueprintReadOnly, Category="SpacetimeDB")
    FSpacetimeDBIdentity LocalIdentity;

protected:
    virtual void BeginPlay() override;
    virtual void EndPlay(const EEndPlayReason::Type EndPlayReason) override;
public:
    virtual void Tick(float DeltaTime) override;

private:
    UFUNCTION() void HandleConnect(UDbConnection* InConn, FSpacetimeDBIdentity Identity, const FString& Token);
    UFUNCTION() void HandleConnectError(const FString& Error);
    UFUNCTION() void HandleDisconnect(UDbConnection* InConn, const FString& Error);
    UFUNCTION() void HandleSubscriptionApplied(FSubscriptionEventContext& Context);
};

Source (GameManager.cpp)

cpp

#include "GameManager.h"
#include "Connection/Credentials.h"

AGameManager* AGameManager::Instance = nullptr;

AGameManager::AGameManager()
{
    PrimaryActorTick.bCanEverTick = true;
    PrimaryActorTick.bStartWithTickEnabled = true;
}

void AGameManager::BeginPlay()
{
    Super::BeginPlay();
    Instance = this;

    FOnConnectDelegate ConnectDelegate;
    BIND_DELEGATE_SAFE(ConnectDelegate, this, AGameManager, HandleConnect);
    FOnDisconnectDelegate DisconnectDelegate;
    BIND_DELEGATE_SAFE(DisconnectDelegate, this, AGameManager, HandleDisconnect);
    FOnConnectErrorDelegate ConnectErrorDelegate;
    BIND_DELEGATE_SAFE(ConnectErrorDelegate, this, AGameManager, HandleConnectError);

    UCredentials::Init(TEXT(".spacetime_token"));
    FString Token = UCredentials::LoadToken();

    UDbConnectionBuilder* Builder = UDbConnection::Builder()
        ->WithUri(ServerUri)
        ->WithDatabaseName(DatabaseName)
        ->OnConnect(ConnectDelegate)
        ->OnDisconnect(DisconnectDelegate)
        ->OnConnectError(ConnectErrorDelegate);

    if (!Token.IsEmpty())
    {
        Builder->WithToken(Token);
    }

    Conn = Builder->Build();
}

void AGameManager::EndPlay(const EEndPlayReason::Type EndPlayReason)
{
    if (Conn) { Conn->Disconnect(); Conn = nullptr; }
    if (Instance == this) { Instance = nullptr; }
    Super::EndPlay(EndPlayReason);
}

void AGameManager::Tick(float DeltaTime)
{
    if (Conn && Conn->IsActive())
    {
        Conn->FrameTick();
    }
}

void AGameManager::HandleConnect(UDbConnection* InConn, FSpacetimeDBIdentity Identity, const FString& Token)
{
    LocalIdentity = Identity;
    UCredentials::SaveToken(Token);

    FOnSubscriptionApplied AppliedDelegate;
    BIND_DELEGATE_SAFE(AppliedDelegate, this, AGameManager, HandleSubscriptionApplied);
    Conn->SubscriptionBuilder()
        ->OnApplied(AppliedDelegate)
        ->SubscribeToAllTables();
}

void AGameManager::HandleConnectError(const FString& Error)
{
    UE_LOG(LogTemp, Error, TEXT("Connection error: %s"), *Error);
}

void AGameManager::HandleDisconnect(UDbConnection* InConn, const FString& Error)
{
    UE_LOG(LogTemp, Warning, TEXT("Disconnected: %s"), *Error);
}

void AGameManager::HandleSubscriptionApplied(FSubscriptionEventContext& Context)
{
    UE_LOG(LogTemp, Log, TEXT("Subscription applied - game state loaded"));
}

FrameTick -- Critical

You must either call
Conn->FrameTick()
every frame in your Actor's
Tick()
, or call
Conn->SetAutoTicking(true)
once at startup. The SDK queues all network messages and only processes them on tick. Without one of these, no callbacks fire and the client appears frozen.

Connection Builder

Build a connection with the builder pattern. All builder methods return pointers for chaining with

->

cpp

UDbConnection* Conn = UDbConnection::Builder()
    ->WithUri(TEXT("127.0.0.1:3000"))
    ->WithDatabaseName(TEXT("my-module"))
    ->WithToken(SavedToken)                              // optional
    ->WithCompression(ESpacetimeDBCompression::Gzip)     // optional
    ->OnConnect(ConnectDelegate)
    ->OnConnectError(ErrorDelegate)
    ->OnDisconnect(DisconnectDelegate)
    ->Build();

OnConnect callback signature

cpp

UFUNCTION()
void OnConnected(UDbConnection* Connection, FSpacetimeDBIdentity Identity, const FString& Token);

Save the

Token

for future reconnection. The

Identity

is the user's persistent identifier.

Subscribing to Tables

After connecting, subscribe to receive table data:

cpp

// Subscribe to all public tables
Conn->SubscriptionBuilder()
    ->OnApplied(AppliedDelegate)
    ->SubscribeToAllTables();

// Subscribe to specific queries
TArray<FString> Queries = { TEXT("SELECT * FROM player"), TEXT("SELECT * FROM entity") };
Conn->SubscriptionBuilder()
    ->OnApplied(AppliedDelegate)
    ->OnError(ErrorDelegate)
    ->Subscribe(Queries);

Subscription Handle

Subscribe

and

SubscribeToAllTables

return a

USubscriptionHandle*

cpp

USubscriptionHandle* Handle = Conn->SubscriptionBuilder()->...->Subscribe(Queries);
Handle->IsActive();      // true while subscription is live
Handle->Unsubscribe();   // cancel the subscription
Handle->UnsubscribeThen(OnEndDelegate); // cancel with callback
Handle->GetQuerySqls();  // get the SQL queries

For views with arguments (2.13+), use only raw SQL

SELECT * FROM view_name(literal_args)

. Use explicit queries for every table on that connection, not subscribe-all. All argument values share one cache table; unsubscribe from obsolete arguments to avoid combining their rows. Validate/encode dynamic values as SQL literals rather than concatenating untrusted input.

Reading the Client Cache

Access tables through

Conn->Db

cpp

// Find by unique/primary key (returns by value; default-constructed if not found)
FUserType User = Conn->Db->User->Identity->Find(SomeIdentity);

// Filter by BTree index
TArray<FPlayerType> LevelFive = Conn->Db->Player->Level->Filter(5);

// Iterate all rows
TArray<FEntityType> AllEntities = Conn->Db->Entity->Iter();

// Count
int32 Total = Conn->Db->Player->Count();

Row Callbacks

cpp

// OnInsert
Conn->Db->User->OnInsert.AddDynamic(this, &AMyActor::OnUserInsert);

// OnDelete
Conn->Db->User->OnDelete.AddDynamic(this, &AMyActor::OnUserDelete);

// OnUpdate (only fires for rows with a primary key)
Conn->Db->User->OnUpdate.AddDynamic(this, &AMyActor::OnUserUpdate);

Callback signatures (must be UFUNCTION)

cpp

UFUNCTION()
void OnUserInsert(const FEventContext& Context, const FUserType& NewRow);

UFUNCTION()
void OnUserDelete(const FEventContext& Context, const FUserType& DeletedRow);

UFUNCTION()
void OnUserUpdate(const FEventContext& Context, const FUserType& OldRow, const FUserType& NewRow);

HandleSubscriptionApplied

Calling Reducers

Invoke reducers through

Conn->Reducers

cpp

Conn->Reducers->SendMessage(TEXT("Hello!"));
Conn->Reducers->SetName(TEXT("Alice"));
Conn->Reducers->MovePlayer(1.0f, 0.0f);

Reducer Result Callbacks

Observe when a reducer you called completes:

cpp

Conn->Reducers->OnSendMessage.AddDynamic(this, &AMyActor::OnSendMessageResult);

cpp

UFUNCTION()
void OnSendMessageResult(const FReducerEventContext& Context, const FString& Text)
{
    UE_LOG(LogTemp, Log, TEXT("SendMessage result for: %s"), *Text);
}

These delegates fire only for reducer calls made by this connection, not for other clients' calls.

Delegate Binding with BIND_DELEGATE_SAFE

Use the

BIND_DELEGATE_SAFE

macro to safely bind delegates to member functions:

cpp

FOnConnectDelegate ConnectDelegate;
BIND_DELEGATE_SAFE(ConnectDelegate, this, AMyActor, HandleConnect);

This is the recommended pattern for all SpacetimeDB delegate bindings in C++.

Identity and ConnectionId

cpp

// FSpacetimeDBIdentity -- 256-bit unique user identifier, persists across connections
FSpacetimeDBIdentity Identity;
Identity.ToHex();

// FSpacetimeDBConnectionId -- 128-bit per-session connection identifier
FSpacetimeDBConnectionId ConnId = Conn->GetConnectionId();

// From any context
FSpacetimeDBIdentity Id;
bool Found = Context.TryGetIdentity(Id);
FSpacetimeDBConnectionId CId = Context.GetConnectionId();

Token Persistence

Use the built-in

UCredentials

helper to save and load tokens. Passing the saved server-issued token back on reconnect keeps the same identity. This token does not expire and a lost one can't be recovered, so self-issued identities are for development. For production, authenticate with an OIDC provider such as SpacetimeAuth, which handles token lifecycle.

cpp

UCredentials::Init(TEXT(".spacetime_token"));
FString Token = UCredentials::LoadToken();
// ... after connect:
UCredentials::SaveToken(Token);

Context Types

All callbacks receive a context struct that provides access to

Db

and

Reducers

Type	Used In
`FEventContext`	Table row callbacks (OnInsert, OnDelete, OnUpdate)
`FReducerEventContext`	Reducer result callbacks
`FSubscriptionEventContext`	Subscription lifecycle callbacks (OnApplied, OnError)
`FErrorContext`	Error callbacks

All inherit from

FContextBase

which provides:

cpp

Context.Db          // URemoteTables* -- client cache
Context.Reducers    // URemoteReducers* -- invoke reducers
Context.SubscriptionBuilder()  // start a new subscription

Blueprint Integration

All core classes are Blueprint-accessible via

UFUNCTION(BlueprintCallable)

and

UPROPERTY(BlueprintReadOnly/BlueprintAssignable)

UDbConnection::Builder()

and all builder methods are

BlueprintCallable

Table callbacks (

OnInsert

OnDelete

OnUpdate

) are

BlueprintAssignable

delegates.

Reducer invoke methods and result delegates are Blueprint-accessible.
```
Conn->Db
```
and
```
Conn->Reducers
```
are
```
BlueprintReadOnly
```
properties.
Generated row types are
```
BlueprintType
```
USTRUCTs with
```
BlueprintReadWrite
```
properties.

This means you can build the entire connection and callback flow in Blueprints without writing C++.

Unreal-Specific Considerations

Auto Ticking Alternative

UDbConnection

inherits from

FTickableGameObject

, but auto ticking is off by default. You have two options:

cpp

// Option 1: Call FrameTick() manually in your Actor's Tick() (shown in GameManager above)
void Tick(float DeltaTime) { Conn->FrameTick(); }

// Option 2: Enable auto ticking. The SDK then processes messages every frame automatically
Conn->SetAutoTicking(true);

Pick one. Without either, no callbacks fire.

Compression

cpp

Builder->WithCompression(ESpacetimeDBCompression::Gzip);  // default
Builder->WithCompression(ESpacetimeDBCompression::None);   // no compression

Generated Types

Codegen produces USTRUCTs prefixed with

(e.g.,

FUserType

FEntityType

) and table classes prefixed with