# Switch a template to Postgres

The [project templates](/docs/reference/templates) record runs with the in-memory provider, which
loses them on restart, shares nothing between processes, and leaves `mode: QUEUE` refused with
`TRAX_QUEUE_UNAVAILABLE`. These steps move Trax's own tables to Postgres.

1. Start a Postgres and add the provider package, at the version the project's other `Trax.*`
   packages already have in `Directory.Packages.props`:

   ```bash
   docker run -d --name trax-db -p 127.0.0.1:5432:5432 \
     -e POSTGRES_USER=trax -e POSTGRES_PASSWORD=trax123 -e POSTGRES_DB=trax postgres:17
   dotnet add package Trax.Effect.Data.Postgres --version <the Trax.Effect version>
   ```

2. Put the connection string in `appsettings.Development.json`:

   ```json
   {
     "ConnectionStrings": {
       "TraxDatabase": "Host=localhost;Port=5432;Database=trax;Username=trax;Password=trax123"
     }
   }
   ```

3. In `Program.cs`, add `using Trax.Effect.Data.Postgres.Extensions;` and replace `UseInMemory()`
   in `AddEffects` with:

   ```csharp fragment
   effects.UsePostgres(
       builder.Configuration.GetConnectionString("TraxDatabase")
           ?? throw new InvalidOperationException("Set ConnectionStrings:TraxDatabase.")
   )
   ```

4. Run the host. Trax creates and migrates its `trax` schema at startup, and the dashboard's runs
   now survive a restart.

With a database, the scheduler queues work in it and runs it on local workers, so a
`[TraxMutation]` called with `mode: QUEUE` runs, and several processes on one database share the
work. `HelloWorldTrain` exposes `Run` only; change its `[TraxMutation(GraphQLOperation.Run)]` to
`[TraxMutation]` to serve the queue mode too.

The application context, `AppDbContext`, is separate and stays in memory. To move it, add
`Npgsql.EntityFrameworkCore.PostgreSQL` and change its `UseInMemoryDatabase("app")` to
`UseNpgsql(...)`; its tables go under the schema in `Data/AppSchema.cs`.

The schema changes each release applies are listed in
[Schema migrations](/docs/reference/schema-migrations).

## SDK Reference

> [UsePostgres](/docs/sdk-reference/configuration/use-postgres) | [UseInMemory](/docs/sdk-reference/configuration/use-in-memory) | [TraxQuery / TraxMutation](/docs/sdk-reference/graphql-api/trax-graphql-attribute)