Why should you care?

Stock changes constantly (sales, returns, warehouse sync). Splitting Inventory prevents catalog deploys from breaking stock counts.

See it live — copy this example

Create a Web API project (dotnet new webapi), paste the code, then run dotnet run.

app.MapGet("/inventory/{productId:int}", async (int productId, InventoryDbContext db) =>
{
    var row = await db.Stock.FindAsync(productId);
    return row is null ? Results.NotFound() : Results.Ok(new { productId, row.Available });
});

app.MapPost("/inventory/reserve", async (ReserveStockDto dto, InventoryDbContext db) =>
{
    var row = await db.Stock.FindAsync(dto.ProductId)
        ?? throw new InvalidOperationException("SKU not found");
    if (row.Available < dto.Qty) return Results.Conflict("Insufficient stock");
    row.Available -= dto.Qty;
    row.Reserved += dto.Qty;
    await db.SaveChangesAsync();
    return Results.Ok();
});

Run Example »

Edit the code and click Run — like W3Schools Try it Yourself.

What happened?

• Reserve moves units from Available to Reserved when order starts.
• Commit or release happens on payment success/failure — saga in module 4.

Try it yourself

1. Create Inventory.Api with Stock table (ProductId, Available, Reserved).
2. Seed stock for products from Product service ids.
3. build GET and POST reserve.
4. Change a string or route in the example and save — watch Swagger or the RabbitMQ Management UI update.
5. Break the code on purpose (remove a semicolon), read the error message, then fix it.

Remember

Inventory owns stock counts and reserve/commit. Overselling is fought with reservations + saga compensation. Product catalog displays stock; Inventory enforces it.

Real-world: Flipkart oversell incident

Without reserve, two customers buy last TV simultaneously. Inventory service serializes reserve with transaction or optimistic concurrency.

Outcome: Only one checkout wins; other gets clear "out of stock" message.