TrainDiscovery

ITrainDiscoveryService scans the DI container for all registered IServiceTrain<TIn, TOut> implementations and returns structured metadata about each one. It lives in Trax.Mediator and is used by both the Dashboard (train listing) and the API layer (input schema generation, train lookup by name).

Registered automatically by AddMediator() as a singleton.

ITrainDiscoveryService

public interface ITrainDiscoveryService
{
    IReadOnlyList<TrainRegistration> DiscoverTrains();
}

DiscoverTrains

Returns all discovered train registrations. Results are cached after the first call — subsequent calls return the same list.

Returns: IReadOnlyList<TrainRegistration>

TrainRegistration

Represents a single discovered train in the DI container.

public class TrainRegistration
{
    public required Type ServiceType { get; init; }
    public required Type ImplementationType { get; init; }
    public required Type InputType { get; init; }
    public required Type OutputType { get; init; }
    public required ServiceLifetime Lifetime { get; init; }
 
    public required string ServiceTypeName { get; init; }
    public required string ImplementationTypeName { get; init; }
    public required string InputTypeName { get; init; }
    public required string OutputTypeName { get; init; }
 
    public required IReadOnlyList<string> RequiredPolicies { get; init; }
    public required IReadOnlyList<string> RequiredRoles { get; init; }
 
    public required bool IsQuery { get; init; }
    public required bool IsMutation { get; init; }
    public required bool IsBroadcastEnabled { get; init; }
    public string? GraphQLName { get; init; }
    public string? GraphQLDescription { get; init; }
    public string? GraphQLDeprecationReason { get; init; }
    public required GraphQLOperation GraphQLOperations { get; init; }
}

Properties

Property	Type	Description
`ServiceType`	`Type`	The interface or concrete type registered in DI (e.g. `IProcessOrderTrain`)
`ImplementationType`	`Type`	The concrete class (e.g. `ProcessOrderTrain`)
`InputType`	`Type`	The `TInput` generic argument from `IServiceTrain<TInput, TOutput>`
`OutputType`	`Type`	The `TOutput` generic argument
`Lifetime`	`ServiceLifetime`	DI lifetime (`Singleton`, `Scoped`, `Transient`)
`ServiceTypeName`	`string`	Friendly display name for `ServiceType` (e.g. `IServiceTrain<OrderInput, OrderResult>`)
`ImplementationTypeName`	`string`	Friendly display name for `ImplementationType`
`InputTypeName`	`string`	Friendly display name for `InputType`
`OutputTypeName`	`string`	Friendly display name for `OutputType`
`RequiredPolicies`	`IReadOnlyList<string>`	Authorization policy names from `[TraxAuthorize]` attributes on the implementation class. Empty if no auth required.
`RequiredRoles`	`IReadOnlyList<string>`	Role names from `[TraxAuthorize(Roles = "...")]` attributes. Empty if no roles required.
`IsQuery`	`bool`	Whether the train has a `[TraxQuery]` attribute and will be exposed as a typed GraphQL query.
`IsMutation`	`bool`	Whether the train has a `[TraxMutation]` attribute and will be exposed as typed GraphQL mutation(s).
`IsBroadcastEnabled`	`bool`	Whether the train has a `[TraxBroadcast]` attribute and will broadcast lifecycle events to subscribers.
`GraphQLName`	`string?`	Custom name override from `[TraxQuery(Name = "...")]` or `[TraxMutation(Name = "...")]`. Null means auto-derived.
`GraphQLDescription`	`string?`	Description for the generated GraphQL fields.
`GraphQLDeprecationReason`	`string?`	If non-null, the generated fields are marked as deprecated.
`GraphQLOperations`	`GraphQLOperation`	Which mutation operations (Run, Queue, or both) to generate. Only applies when `IsMutation` is true. Defaults to `Run`.

How Discovery Works

Iterates every ServiceDescriptor in IServiceCollection.
For each descriptor, checks whether the service type (or any of its interfaces) is a closed generic of IServiceTrain<,>.
Skips concrete-type registrations that come from the dual-registration pattern (AddScopedTraxRoute registers both TImplementation and TService).
Extracts InputType and OutputType from the generic arguments.
Deduplicates by InputType: when multiple registrations share the same input type (interface + concrete from dual-registration), prefers the interface as ServiceType and the concrete class as ImplementationType.
Reads [TraxAuthorize] attributes from the implementation type and extracts policy and role requirements into RequiredPolicies and RequiredRoles. 6b. Reads [TraxQuery] and [TraxMutation] attributes from the implementation type and populates IsQuery, IsMutation, GraphQLName, GraphQLDescription, GraphQLDeprecationReason, and GraphQLOperations. 6c. Reads the [TraxBroadcast] attribute and populates IsBroadcastEnabled.
Caches the result — the list is computed once and reused for the lifetime of the service.

Example

public class TrainListController(ITrainDiscoveryService discovery) : ControllerBase
{
    [HttpGet("trains")]
    public IActionResult GetTrains()
    {
        var trains = discovery.DiscoverTrains();
 
        return Ok(trains.Select(t => new
        {
            t.ServiceTypeName,
            t.ImplementationTypeName,
            t.InputTypeName,
            t.OutputTypeName,
            Lifetime = t.Lifetime.ToString()
        }));
    }
}

Package

dotnet add package Trax.Mediator