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Docs: Fix linting error and misc. changes
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@mysticmind
mysticmind committed Jul 25, 2024
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37 changes: 30 additions & 7 deletions docs/scenarios/command_handler_workflow.md
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Expand Up @@ -62,7 +62,7 @@ public class Order
}
}
```
<sup><a href='https://github.com/JasperFx/marten/blob/master/src/EventSourcingTests/Examples/OptimizedCommandHandling.cs#L21-L59' title='Snippet source file'>snippet source</a> | <a href='#snippet-sample_order_for_optimized_command_handling' title='Start of snippet'>anchor</a></sup>
<sup><a href='https://github.com/JasperFx/marten/blob/master/src/EventSourcingTests/Examples/OptimizedCommandHandling.cs#L23-L61' title='Snippet source file'>snippet source</a> | <a href='#snippet-sample_order_for_optimized_command_handling' title='Start of snippet'>anchor</a></sup>
<!-- endSnippet -->

And with some events like these:
Expand All @@ -76,7 +76,7 @@ public record OrderReady;

public record ItemReady(string Name);
```
<sup><a href='https://github.com/JasperFx/marten/blob/master/src/EventSourcingTests/Examples/OptimizedCommandHandling.cs#L11-L19' title='Snippet source file'>snippet source</a> | <a href='#snippet-sample_order_events_for_optimized_command_handling' title='Start of snippet'>anchor</a></sup>
<sup><a href='https://github.com/JasperFx/marten/blob/master/src/EventSourcingTests/Examples/OptimizedCommandHandling.cs#L13-L21' title='Snippet source file'>snippet source</a> | <a href='#snippet-sample_order_events_for_optimized_command_handling' title='Start of snippet'>anchor</a></sup>
<!-- endSnippet -->

Let's jump right into the first sample with simple concurrency handling:
Expand Down Expand Up @@ -113,7 +113,7 @@ public async Task Handle1(MarkItemReady command, IDocumentSession session)
await session.SaveChangesAsync();
}
```
<sup><a href='https://github.com/JasperFx/marten/blob/master/src/EventSourcingTests/Examples/OptimizedCommandHandling.cs#L66-L97' title='Snippet source file'>snippet source</a> | <a href='#snippet-sample_fetch_for_writing_naive' title='Start of snippet'>anchor</a></sup>
<sup><a href='https://github.com/JasperFx/marten/blob/master/src/EventSourcingTests/Examples/OptimizedCommandHandling.cs#L68-L99' title='Snippet source file'>snippet source</a> | <a href='#snippet-sample_fetch_for_writing_naive' title='Start of snippet'>anchor</a></sup>
<!-- endSnippet -->

In this usage, `FetchForWriting<Order>()` is finding the current state of the stream based on the stream id we passed in. If the `Order` aggregate
Expand Down Expand Up @@ -189,7 +189,7 @@ public async Task Handle2(MarkItemReady command, IDocumentSession session)
await session.SaveChangesAsync();
}
```
<sup><a href='https://github.com/JasperFx/marten/blob/master/src/EventSourcingTests/Examples/OptimizedCommandHandling.cs#L99-L133' title='Snippet source file'>snippet source</a> | <a href='#snippet-sample_fetch_for_writing_explicit_optimistic_concurrency' title='Start of snippet'>anchor</a></sup>
<sup><a href='https://github.com/JasperFx/marten/blob/master/src/EventSourcingTests/Examples/OptimizedCommandHandling.cs#L101-L135' title='Snippet source file'>snippet source</a> | <a href='#snippet-sample_fetch_for_writing_explicit_optimistic_concurrency' title='Start of snippet'>anchor</a></sup>
<!-- endSnippet -->

In this case, Marten will throw a `ConcurrencyException` if the expected starting version being passed to `FetchForWriting()` has
Expand Down Expand Up @@ -237,7 +237,7 @@ public async Task Handle3(MarkItemReady command, IDocumentSession session)
await session.SaveChangesAsync();
}
```
<sup><a href='https://github.com/JasperFx/marten/blob/master/src/EventSourcingTests/Examples/OptimizedCommandHandling.cs#L135-L169' title='Snippet source file'>snippet source</a> | <a href='#snippet-sample_sample_fetch_for_writing_exclusive_lock' title='Start of snippet'>anchor</a></sup>
<sup><a href='https://github.com/JasperFx/marten/blob/master/src/EventSourcingTests/Examples/OptimizedCommandHandling.cs#L137-L171' title='Snippet source file'>snippet source</a> | <a href='#snippet-sample_sample_fetch_for_writing_exclusive_lock' title='Start of snippet'>anchor</a></sup>
<!-- endSnippet -->

Do note that the `FetchForExclusiveWriting()` command can time out if it is unable to achieve a lock in a timely manner. In this case,
Expand Down Expand Up @@ -277,15 +277,38 @@ public Task Handle4(MarkItemReady command, IDocumentSession session)
});
}
```
<sup><a href='https://github.com/JasperFx/marten/blob/master/src/EventSourcingTests/Examples/OptimizedCommandHandling.cs#L171-L198' title='Snippet source file'>snippet source</a> | <a href='#snippet-sample_using_writetoaggregate' title='Start of snippet'>anchor</a></sup>
<sup><a href='https://github.com/JasperFx/marten/blob/master/src/EventSourcingTests/Examples/OptimizedCommandHandling.cs#L173-L200' title='Snippet source file'>snippet source</a> | <a href='#snippet-sample_using_writetoaggregate' title='Start of snippet'>anchor</a></sup>
<!-- endSnippet -->

## Optimizing FetchForWriting with Inline Aggregates

If you are utilizing `FetchForWriting()` for your command handlers -- and you really, really should! -- and at least
some of your aggregates are updated `Inline` as shown below:

snippet: sample_registering_Order_as_Inline
<!-- snippet: sample_registering_Order_as_Inline -->
<a id='snippet-sample_registering_order_as_inline'></a>
```cs
var builder = Host.CreateApplicationBuilder();
builder.Services.AddMarten(opts =>
{
opts.Connection("some connection string");

// The Order aggregate is updated Inline inside the
// same transaction as the events being appended
opts.Projections.Snapshot<Order>(SnapshotLifecycle.Inline);

// Opt into an optimization for the inline aggregates
// used with FetchForWriting()
opts.Projections.UseIdentityMapForInlineAggregates = true;
})

// This is also a performance optimization in Marten to disable the
// identity map tracking overall in Marten sessions if you don't
// need that tracking at runtime
.UseLightweightSessions();
```
<sup><a href='https://github.com/JasperFx/marten/blob/master/src/EventSourcingTests/Examples/OptimizedCommandHandling.cs#L207-L228' title='Snippet source file'>snippet source</a> | <a href='#snippet-sample_registering_order_as_inline' title='Start of snippet'>anchor</a></sup>
<!-- endSnippet -->

You can potentially gain some significant performance optimization by using the `UseIdentityMapForInlineAggregates`
flag shown above. To be clear, this optimization mostly helps when you have the combination in a command handler that:
Expand Down

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