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README

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Get a SpacetimeDB C# app running in under 5 minutes.

Prerequisites

Install the SpacetimeDB CLI before continuing.

Install .NET WASI workload

SpacetimeDB C# modules compile to WebAssembly using the WASI experimental workload.

bash
dotnet workload install wasi-experimental

Create your project

Run the spacetime dev command to create a new project with a C# SpacetimeDB module.

This will start the local SpacetimeDB server, compile and publish your module, and generate C# client bindings.

bash
spacetime dev --template basic-cs

Explore the project structure

Your project contains both server and client code.

Edit spacetimedb/Lib.cs to add tables and reducers. Use the generated bindings in the client project.

my-spacetime-app/
├── spacetimedb/             # Your SpacetimeDB module
│   ├── StdbModule.csproj
│   └── Lib.cs               # Server-side logic
├── client.csproj
├── Program.cs               # Client application
└── module_bindings/         # Auto-generated types

Understand tables and reducers

Open spacetimedb/Lib.cs to see the module code. The template includes a Person table and two reducers: Add to insert a person, and SayHello to greet everyone.

Tables store your data. Reducers are functions that modify data — they're the only way to write to the database.

csharp
using SpacetimeDB;

public static partial class Module
{
    [SpacetimeDB.Table(Accessor = "Person", Public = true)]
    public partial struct Person
    {
        public string Name;
    }

    [SpacetimeDB.Reducer]
    public static void Add(ReducerContext ctx, string name)
    {
        ctx.Db.Person.Insert(new Person { Name = name });
    }

    [SpacetimeDB.Reducer]
    public static void SayHello(ReducerContext ctx)
    {
        foreach (var person in ctx.Db.Person.Iter())
        {
            Log.Info($"Hello, {person.Name}!");
        }
        Log.Info("Hello, World!");
    }
}

Test with the CLI

Open a new terminal and navigate to your project directory. Then use the SpacetimeDB CLI to call reducers and query your data directly.

bash
cd my-spacetime-app

# Call the add reducer to insert a person
spacetime call add Alice

# Query the person table
spacetime sql "SELECT * FROM Person"
 name
---------
 "Alice"

# Call say_hello to greet everyone
spacetime call say_hello

# View the module logs
spacetime logs
2025-01-13T12:00:00.000000Z  INFO: Hello, Alice!
2025-01-13T12:00:00.000000Z  INFO: Hello, World!

Next steps