Create source generators to minimize boilerplate code

[alexeyfv]

Hi,

I recently came up with the idea of creating a source code generator for aggregates because I got tired of writing repetitive boilerplate code.

Let's say we have the following aggregate:

public class OrderAggregate(OrderAggregateId id) : 
    AggregateRoot<OrderAggregate, OrderAggregateId>(id)
{
    public Task DoSomething() 
    {
        // Some code
    }
}

public class OrderAggregateId(string value) :
    Identity<OrderAggregateId>(value);

To update the aggregate, we usually write this

await store.UpdateAsync<OrderAggregate, OrderAggregateId>(
    id,
    SourceId.New,
    (order, _) => order.DoSomething(),
    cancellationToken);

With source generators, we can omit the type declarations, skip the source ID, and avoid the cancellation token:

await store.UpdateAsync(
    id,
    order => order.DoSomething(),
    cancellationToken);

The source code generator creates the following extension method for IAggregateStore

public static class IAggregateStoreExtensions
{
    public static Task<IReadOnlyCollection<IDomainEvent>> UpdateAsync(
        this IAggregateStore aggregateStore,
        OrderAggregateId id,
        Func<OrderAggregate, Task> update,
        CancellationToken cancellationToken) =>
            aggregateStore.UpdateAsync<OrderAggregate, OrderAggregateId>(
                id,
                SourceId.New,
                (aggregate, _) => update(aggregate),
                cancellationToken);

    // other code
}

What do you think about adding something like this to EventFlow?

You can see the full example here.

[rasmus]

Seems simple enough and I'm all for making it easier for developers. Only minor change is that the class should properly be named AggregateStoreExtensions to follow the existing code.