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QueryBus

The QueryBus handles queries (read operations) in a CQRS architecture.

Class Definition​

class QueryBus implements QueryBusInterface {
  constructor(props?: QueryBusConstructorProps);
  
  dispatch<TQuery extends UntypedQueryType>(
    query: TQuery
  ): Promise<QueryResult<TQuery>>;
  
  register<TQuery extends UntypedQueryType>(
    handler: QueryHandlerInterface<TQuery>
  ): void;
}

Constructor​

new QueryBus(props?: QueryBusConstructorProps)​

Creates a new QueryBus instance.

Parameters:

  • props?: QueryBusConstructorProps - Optional configuration 
    interface QueryBusConstructorProps {
      monitoringService?: MonitoringService | null;
    }

Example:

const queryBus = new QueryBus();
// or with options
const queryBus = new QueryBus({
  monitoringService: myMonitoringService,
});

Methods​

register<TQuery>(handler: QueryHandlerInterface<TQuery>): void​

Registers a query handler.

Type Parameters:

  • TQuery - The query type (must extend UntypedQueryType)

Parameters:

  • handler: QueryHandlerInterface<TQuery> - The handler function 
    interface QueryHandlerInterface<TQuery extends UntypedQueryType> {
      (query: TQuery): Promise<TQuery["result"]>;
    }

Example:

queryBus.register(async (query: GetTodosQuery) => {
  return await todosRepository.findAll();
});

dispatch<TQuery>(query: TQuery): Promise<QueryResult<TQuery>>​

Dispatches a query to registered handlers and returns the result.

Type Parameters:

  • TQuery - The query type

Parameters:

  • query: TQuery - The query to dispatch

Returns: Promise<QueryResult<TQuery>> - The query result

Example:

const query = new GetTodosQuery();
const todos = await queryBus.dispatch(query); // Promise<Todo[]>

Interface​

interface QueryBusInterface {
  dispatch<TQuery extends UntypedQueryType>(
    query: TQuery
  ): Promise<QueryResult<TQuery>>;
  
  register<TQuery extends UntypedQueryType>(
    handler: QueryHandlerInterface<TQuery>
  ): void;
}

type QueryResult<TQuery> = TQuery extends QueryInterface<
  string,
  unknown,
  infer TResult
>
  ? TResult
  : never;