Sharpino 3.0.7

Sharpino

<img src="ico/sharpino.png" alt="drawing" width="50"/>

A little F# Event Sourcing Library

What is it?

Support for Event-sourcing in F#.

Overview

• Contexts: event sourced objects with no id, so only one instance is around

• Aggregates: event sourced objecst with id (Guid).

• Non-Saga transactions: execute multiple commands involving different aggregates as single db transactions.

• Sagas-like transactions: execute sequencial multiple commands with undoers (to rollback the transaction in case of failure of any command).

• Cache: Dictionary based cache of the current state of contexts or aggregates.

• Gdpr: functions to overwrite snapshots and events in case the users ask to delete their data.

• SqlTemplates contains skeleton of sql scripts to create tables for events and snapshots in Postgres.

• DbMate command line tool to setup eventstoredb (Postgres) tables (uses the templates to generate the scripts by substitution).

• Optimistic lock: commands will remember the event ids of the specific states of the aggregates involved and such event state ids will be checked again before adding any event to the event store.

• Note: I am not using examples on the basis of a fully distributed architecture and therefore I haven't implemented Kafka or any other message broker. However the library is ready to be extended to use actual message brokers (any command can virtually publish any event after storing them is a "send and forget" style).

Warning: the mini gitbook is outdated.

Info: - The various SAGA-like functions are "under investigation"(more tests and fixes needed). The "malboxprocessor" could also be removed as it has a little potential advantage but less control (in debug for example).

Projects

Sharpino.Lib.Core:

• Core.fs: Abstract definition of Events, Commands and Undoer (or compensator in case of Saga)

Sharpino.Lib:

• CommandHandler.fs: Gets and stores snapshots, executes commands, and produces and stores events using the event store.
• PgEventStore.fs and MemoryStorage.fs: Manages persistence of events in Postgres or in-memory respectively using string encoding (JSON)
• PgBinaryEventStore.fs: Manages persistence of events in Postgres using binary encoding (examples are based on Fspickler external lib)
• Cache.fs. Caches the current state of contexts or aggregates.

Sharpino.Sample: See the sources for the setup, and particularly for the database setup (username/password)

It could be convenient to write the api layer so that it can refer to any eventstore (Postgres, or in-memory) and an actual event broker (Kafka) or a neutral ("doNothing") event broker. There are some facilities in test to run them in a parametrized way respect to the actual instance of the api layer (with the actual db based eventstore or just the in-memory for example).

Warning: some examples may refer to previous version of the library as in the nuget repository. Check the .fsproj to make sure if you want to use them as a blueprint for your experiments/applications aligned with the latest version of the library.

How to use it

• You can run the Sharpino.Sample application as a rest service by running the following command from Sharpino.Sample folder:

dotnet run

• You can run the client Fable/Elmish sample application by running the following command from the Sharpino.Sample.Client folder:

npm install
npm start

• Just use ordinary dotnet command line tools for building the solution. Particularly you can run tests of the sample application by using the following command:

dotnet test 

You can also run the tests by the following command from Sharpino.Sample.Tests folder:

dotnet run

In the latter case, you get the output from Expecto test runner (in this case the console shows eventual standard output/printf).

This pattern is general for all the samles, even though it can changes (just dig into it to figure it out accurately).

By default, the tests run only the in-memory implementation of the storage. You can set up the Postgres tables and db by using dbmate. In the Sharpino.Sample folder you can run the following command to set up the Postgres database:

dbmate -e up

(see the .env to set up the DATABASE_URL environment variable to connect to the Postgres database with a connection string).

SAMPLE 4

Sample 4 uses SAFE stack (Fable/Elmish). The aggregates are rows of seats that I can book. A skeleton of Elmish client is provided.

SAMPLE 5

Sample 5 will just replace SAMPLE 4. uses SAFE stack (Fable/Elmish). Use the common SAFE stack basic operation for running and testing (under the directory Sharpino.Sample.5) Please just look at the domain, and don't care that much about the u.i. (Elmish part).

Tests on eventstoredb. EventStroreDb is not mantained that much at the moment

The following line needs to stay commented out.

        // (AppVersions.evSApp,                    AppVersions.evSApp,                 fun () -> () |> Result.Ok)

Sample application 2 is a problem of booking seats in two rows of five seats.

1. Booking seats among multiple rows (where those rows are aggregates) in an event-sourcing way.
2. Booking seats in a single row by two concurrent commands that singularly do not violate any invariant rule and yet the final state is potentially invalid.

Problem 1

I have two rows of seats related to two different streams of events. Each row has 5 seats. I want to book a seat in row 1 and a seat in row 2. I want to do this in a single transaction so that if just one of the claimed seats is already booked then the entire multiple-row transaction fails and no seats are booked at all.

Problem 2

There is an invariant rule that says that no booking can end up in leaving the only middle seat free in a row. This invariant rule must be preserved even if two concurrent transactions try to book the two left seats and the two right seats independently so violating (together) this invariant.

Sample application 4

The domain Sample application 4 is the same of the Sample 2 and uses aggregates to be able to create an arbitrary number of seat rows. Invariants can be represented by quoted expressions so that, ideally, this may allow us to move toward a DSL (Example: "no booking can end up in leaving the only middle seat free in a row").

Faq:

• Why the name "Sharpino"?
  • It's a mix of "Sharp" (as the '#' of C# or F#) and fino (Italian for "thin"). "sciarpino" (same pronunciation) in Italian means also "little scarf".
• Why another event-sourcing library?
  • I wanted to study the subject and it ended up in a tiny little framework.
• Why F#?
  • Any functional language of the ML family language in my opinion is a good fit for the following reasons:
    • Events are immutable, building the state of the context is a function of those events.
    • Discriminated Unions are suitable to represent events and commands.
    • The use of the lambda expression is a nice trick for the undoers (compensators for using Saga in multiple commands).
    • It is a .net language, so you can use everything in the .net ecosystem (including C# libraries).
• How to use it
  • add the nuget package Sharpino to your project.
  • note: if you gets in a setup errors like "A function labeled with the 'EntryPointAttribute' attribute must be the last declaration" then you may fix by adding this line in the .fsproj file:

  <GenerateProgramFile>false</GenerateProgramFile>
  

Useful info:

Examples 4 and 5 are using the SAFE stack. To run the tests use the common SAFE way (dotnet run and dotnet run -- RunTests from their root dir )

Todo list. Help welcome:

• Rewrite from scratch the Kafka integration making it work as is supposed to (send and and forget with limited retries or transactional outbox pattern). Implement aggregate state viewer based on processing events via messages with some way to resync data when in trouble.
• Implementing event store using Postgres event store but using Azure sql instead.
• Add metadata to events in json format. We should be able to pass those metadata via commands (example runAggregateCommandMd may be the same as runAggregateCommand with metadata added). That must be useful for debugging.
• Write more examples (porting classic DDD examples implemented to test other libraries is fine).
• Write a full-Saga/Process manager for running multiple commands involving arbitrary types. The "compensator"/"undoer" must be able to rollback the transaction in case of failure of any command.
• Add metadata to events in json format. We should be able to pass those metadata via commands (example runAggregateCommandMd may be the same as runAggregateCommand with metadata added). That must be useful for debugging.

Comparison with the style of examples in other event-sourcing libraries

• Equinox

See these examples to compare:

• Counter in Sharpino
• Counter in Equinox
• Invoices in Sharpino
• Invoices in Equinox

Acknowledgements

A heartfelt thank you to Jetbrains who have generously provided free licenses to support this project.

Upcasting techniques.

In this section, I will describe the upcasting techniques that any application may use to allow read snapshots in old format. Goal: using upcast techniques to be able to read the old (serialized) version of typeX into a new version of it.

1. The following premise must be true: If you clone any TypeX into a new one with only a different name (example: TypeX001), then your serialization technique/library must be able to read any stored serialized instance of typeX and get the equivalent instance of TypeX001, so it will be able to indifferently have TypeX and TypeX001 as the target for deserialization (some libraries may allow this out of the box, some other may need some extra config/tuning and/or specific converters).
2. Now you can make some changes to TypeX that make it different from the old TypeX/TypeX001 (example: add new property) making sure that there exists a proper logical conversion (or better: "isomorphic immersion" if you like algebraic terms) from the old TypeX (i.e. TypeX001) into the new TypeX.
3. Define the Upcast function/instance member form TypeX001 that actually implements that conversion from an instance of the old typeX to an instance of the new typeX.
4. Define a "fallback" action in the deserialization related to the new TypeX so that it can, in case of failure because of encountering an old TypeX/TypeX001, apply the deserialization obtaining a typeX001 instance and use its Upcastor to get, finally, the equivalent instance of TypeX.

• Now you can deploy the new version and in case the code tries to read an old TypeX/TypeX001 it must be able to correctly interpret it as the new TypeX by adopting the following steps in deserialization of the existing snapshot:
• try to read and deserialize it as TypeX
• if Ok then Ok
• if it fails try to read it as TypeX001 and then upcast to TypeX

5. If it is not expensive, transform any snapshot of old typeX/TypeX001 into the new TypeX in one shot: make a massive upfront aggregate upcast and re-snapshot: retrieve all the existing current state of aggregates of old TypeX/TypeX001 (that will do upcast under the neath) and generate and store snapshots for all of them so that those snapshot will surely respect the format of the new TypeX. After doing it, assume that the fallback action of reading old versions and then upcasting will never be necessary again and that part of the code can be simply deleted from TypeX.
6. If you decided not to do the previous step 5 or if there is the possibility that you'll need to downgrade the new TypeX again to the previous TypeX001 (which would mean creating a "downcastor" making essentially the reverse of the Upcast process described), then keep the older typeX (or TypeX001) for a while so you will still be able to upcast "on the fly" any older typeX and you will also are prepared to eventually downgrade/downcast again. Note that keeping the TypeX001 around for a long time means that a further upgrade may complicate things as you may have to go deeper in having more older versions in the form of TypeX002, with a more complicated and error-prone recursive chain of fallback/upcast among older versions. So rather you will prefer to doing the full step 7 to make sure that the upgrade will affect all the snapshots.
7. Last but not least. Having events that depend strictly on the old type X format could be a problem because you don't know if that may imply the necessity to change/upcast also the events, or just test the hypothesis that events based on typeX (say Event.Update (x: Type/X)) can be correctly parsed if TypeX changes. If not, then just don't use TypeX as an argument for whatever event.

News/Updates

• Version 2.7.7: The md field is mandatory for any event table: Any run(Aggregate)Commands are redirecting to the equivalent 'run(Aggregate)CommandsMd' that accepts metadata as a string.

• Version 2.7.5: Can view history of events related to a set of aggregates in a time interval (StateView.getFilteredMultipleAggregateEventsInATimeInterval)

• Version 2.7.4: A (quick)fix allows adding compensating events in pgEventstore in saga-ish that were rejected because of strict eventId control

• Live example is here: restaurant management system tech stack: Blazor as Front end, Sharpino as backend, Postgres as event store, Azure as hosting.

• Version 2.7.2: Support metadata field in db (any command has the correspondent commandMd that accepts any string as metadata). Those metadata can be used for debugging purposes. To use them any event table in the db needs a new nullable text field called "md". New db functions are also needed. See the functions like "insert_md{Version}{AggregateStorageName}_events_and_return_id" in the sql scripts in the SqlTemplate dir doing a proper substitution in {Version} and {Format} and {AggregateStorageName}. Similar function is in the ContextTemplate.sql.

• Version 2.7.1: Bug fix

• Version 2.7.0: Fix bug in Saga-ish multi-command and added some tests for it.

• Version 2.6.8: Remove EventStoreDb and starting removing Kafka (for future rewrite or replacement).

• Version 2.6.7: Optimize snapshotting by using the in-memory cached value to avoid multiple reads of the same aggregate.

• Version 2.6.6: Can create new snapshots for aggregates that have no events yet (can happen when you want to do massive upcast/snapshot for any aggregate)

• Version 2.6.4: the mkAggregateSnapshots and mkSnapshots are now public in commandhandler so that they can be used in the user application to create snapshots of the aggregates and contexts. This is userful after an aggregate refactoring update so that any application can do upcast of all aggregates and then store them as snapshots (and then foreget about the need to keep upcast logic active i.e. can get rid of any older version upcast chain).

• Version 2.6.3: Stateview added getFilteredAggregateSnapshotsInATimeIntervalwhich returns a list of snapshots of a specific type/version of aggregate in a time interval filtered by some criteria no matter if any context contains references to those aggregates, so you can retrieve aggregates even if no context has references to them (for instance "inactive users").

• Version 2.6.2: CommandHandler, PgEventStore and PgBinaryEventstore expose as setLogger (newLogger: Ilogger) based on the ILogger interface replacing Log4net. You can then pass that value after retrieving it from the DI container (straightforward in a .net core/asp.net app).

• Version 2.6.0: Added a function for the GDPR in command handler able to virtuallty delete snapshots and events, i.e. replace any event with an events that returns an empty version of the state and also replace any snapshot with the voided/empty version of that state (and also fill the cache with that empty value).

• Version 2.5.9: Added the possibility via StateView to retrieve the initial state/initial snapshot of any aggregate to allow retrieving the data that the users claims. So when users unsubscribe to any app then they have the rights to get any data. This is possibile by getting the initial states and any following event. I think it will be ok to give the user a json of the initial snapshots and any events via an anonymous record and then let the use download that JSON.

• Version 2.5.8: Added query for aggregate events in a time interval. StateView/Readmodel can use it passing a predicate to filter events (example: Query all the payment events). Aggregate should not keep those list ob objects to avoid unlimited grow.

• A short pdf: why do we need upcastors for aggregates and not for events (sorry for typos)

• Blog post: Upcasting aggregates in Sharpino

• Blog post: comparing the example of the "Counter" app in Equnox and in Sharpino https://medium.com/@tonyx1/equinox-vs-sharpino-comparing-the-counter-example-0e2bd6e9bbf2

• Version 2.5.7 added mixtures of saga-like multi-commands and saga-less multi-aggregate commands (not ideal at all, but useful for some use cases that I found that I will describe later, I hope)

• Blogged About Sharpino. An Event Shourcing library

• Version 2.5.4 added runInitAndTwoAggregateCommands that creates a new aggregate snapshot and run two commands in a single transaction.

• Version 2.5.3 added runSagaThreeNAggregateCommands this is needed when transaction cannot be simultaneous for instance when it needs to involve the same aggregate in multiple commands. (A short example will come but here is an idea, pretending the aggregate types can be two, and not three: A1, A2, A3, A3 needs to merge into An: I cannot run the "indpendent" saga-free version of running multiple commands (pairs) because I should repeat the id of An many times which is invalid, so I run the saga version that executes the single "merge" i.e. merge A1 into An, then merge A2 into An etc...: if somethings goes wrong I have accuulted the "future undoers" that may rollback the eventually suffessful merges)

• A "porting" of an example from Equinox https://github.com/tonyx/sharpinoinvoices

• Version 2.5.2. add the runThreeNAggregateCommands (means being able to run simultaneusly n-ples of commands related to three different kind of aggregates)!

• Kafka status: No update. Use the only database version of the events and the "doNothing" broker for (not) publishing.

• Version 4.5.0 changed the signature of any command in user application. Commands and AggregateCommands return also the new computed state and not only the related events. Example:

                | UpdateName name -> 
                    dish.UpdateName name
                    |> Result.map (fun x -> (x, [NameUpdated name]))

Any application needs a little rewrite in the command part (vim macros may be helpful).

In this way the commandhandler takes advantage of it to be able to memoize the state in the cache, so that virtually the state will never be processed and at any state the cache will always be ready for the current state (unless the system restarts, and in that case the state will be taken by reading the last snapshot and processing the events from that point on).

• Version 2.4.2: Added a constraints that forbids using the same aggregate for multiple commands in the same transaction. The various version of RunMultiCommands are not ready to guarantee that they can always work in a consistent way when this happens.
• Disable Kafka on notification and subscribtion as well. Just use the "donothingbroker" until I go back on this and fix it. This is a sample of the doNothingBroker:

    let doNothingBroker =
        {
            notify = None
            notifyAggregate = None
        }

• Version 2.4.0: for aggregate commands use the AggregateCommand<..> interface instead of Aggregate<..> The undoer has changed its signature.

Usually the way we run commands against multiple aggregate doesn't require undoer, however it may happen. Plus: I am planning to use the undoer in the future for the proper user level undo/redo feature.

An example of the undoer for an aggregate is in the following module.

module CartCommands =
    type CartCommands =
    | AddGood of Guid * int
    | RemoveGood of Guid
        interface AggregateCommand<Cart, CartEvents> with
            member this.Execute (cart: Cart) =
                match this with
                | AddGood (goodRef, quantity) -> 
                    cart.AddGood (goodRef, quantity)
                    |> Result.map (fun s -> (s, [GoodAdded (goodRef, quantity)]))
                | RemoveGood goodRef ->
                    cart.RemoveGood goodRef
                    |> Result.map (fun s -> (s, [GoodRemoved goodRef]))
            member this.Undoer = 
                match this with
                | AddGood (goodRef, _) -> 
                    Some 
                        (fun (cart: Cart) (viewer: AggregateViewer<Cart>) ->
                            result {
                                let! (i, _) = viewer (cart.Id) 
                                return
                                    fun () ->
                                        result {
                                            let! (j, state) = viewer (cart.Id)
                                            let! isGreater = 
                                                (j >= i)
                                                |> Result.ofBool (sprintf "execution undo state '%d' must be after the undo command state '%d'" j i)
                                            let result =
                                                state.RemoveGood goodRef
                                                |> Result.map (fun _ -> [GoodRemoved goodRef])
                                            return! result
                                        }
                                }
                        )
                | RemoveGood goodRef ->
                    Some
                        (fun (cart: Cart) (viewer: AggregateViewer<Cart>) ->
                            result {
                                let! (i, state) = viewer (cart.Id) 
                                let! goodQuantity = state.GetGoodAndQuantity goodRef
                                return
                                    fun () ->
                                        result {
                                            let! (j, state) = viewer (cart.Id)
                                            let! isGreater = 
                                                // this check depends also on the number of events generated by the command (i.e. the j >= (i+1) if command generates 2 event)
                                                (j >= i)
                                                |> Result.ofBool (sprintf "execution undo state '%d' must be after the undo command state '%d'" j i)
                                            let result =
                                                state.AddGood (goodRef, goodQuantity)
                                                |> Result.map (fun _ -> [GoodAdded (goodRef, goodQuantity)])
                                            return! result
                                        }
                                }
                        )

• WARNING!!! Version 2.2.9 is DEPRECATED. Fixing it.
• Version 2.2.9: introduced timeout in connection with postgres as eventstore. Plus more error control. New parameter in sharpinoSeettings.json needed:

{
    "LockType":{"Case":"Optimistic"},
    "RefreshTimeout": 100,
    "CacheAggregateSize": 100,
    "PgSqlJsonFormat":{"Case":"PlainText"},
    "MailBoxCommandProcessorsSize": 100,
    "EventStoreTimeout": 100
}

• Version 2.2.8: renamed the config from appSettings.json to sharpinoSettings.json. An example of the config file is as follows:

{
    "LockType":{"Case":"Optimistic"},
    "RefreshTimeout": 100,
    "CacheAggregateSize": 100,
    "PgSqlJsonFormat":{"Case":"PlainText"},
    "MailBoxCommandProcessorsSize": 100
}

Example of line in your .fsproj or .csproj file:

  <ItemGroup>
    <None Include="sharpinoSettings.json" CopyToOutputDirectory="PreserveNewest" />
  </ItemGroup>

• Changes to the classic Blazor counter app to use Sharpino in the backend: https://github.com/tonyx/blazorCounterSharpino.git

• Version 2.2.6: runCommands work in threads for aggregates and context using mailboxprocessors for aggregates (the number of those active mailboxprocessors can be limited in config)

• Version 2.2.5: fix runCommand eventbroker notification.

• Version 2.2.4: some changes in runCommand: no need to pass state and aggregateViewer as it will just use the ones based on the eventstore (source of truth). Supporting also net7.0. The "core" gets rid of TailCall attribute not compatible with net7.0. There is the possibility that including Sharpino.Core must be explicitly included. For an example of app that has been upagraded to the newest version of library see shopping cart

• Version 2.1.3: added local fork of FsKafka (with library dependencies updated) to be able to use it in the project.

• Version 2.1.0: going to remove newtonsoft, introduced FsPickler, FsKafka, changed kafka publisher way (binary and textencoding). Removed Kafkareceiver. Preparing to replace it with one based on FSKafka

• I am porting the examples to use the newer version (2.0.6). The porting of the first example(Sharpino.Sample) is incomplete (At the moment I disabled the "migrate between version" function in that example).

• version 2.0.7: a fix in runThreeCommand. CommandHandler will just use fresh data ignoring the viewer that has been passed.

• version 2.0.6:

  • eventstore checks the eventId of the state that produces any event before adding them. That will ensure that events are added in the right order and cannot fail (so the optimistic lock stateId will be superfluous and will be dropped). Serialization can be binary or JSON (see appSettings.json). The default is binary. The samples use Fspickler to serialize/deserialize events and snapshots. There is no use of ISerializer interface which was by default newtonsoft. Therefore the user needs to provide a serializer (pickler is ok for binary and for json as well). Pickler will not work with jsonb fields in Postgres as the indexes change their order in jsonb and pickler doesn't want it, so they must be text. Kafka is still not working on the read part. The write part is ok even though any read test has been dropped for incompatibility and will be rewritten.

• version 2.0.3: changes from "now()" to utcNow() format in eventstores (Postgres and inMemory) and Sql template scripts.

• published version 2.0.0 supporting binary serialization for events and snapshots on Postgres. Note: the current examples provided are still referencing the previous 1.6.6 version. Here is an example compatible with 2.0.0. with binary serialization

• Old videos (I need to review them because they may contain some errors or outdated info):

https://youtu.be/OQKD5uluFPc https://youtu.be/ToZ_I_xRA-g https://youtu.be/WtGEQqznPnQ https://youtu.be/j2XoLkCt31c

• added a few new examples (can be used for dojos) pub system
• version 1.6.6: can use plain text instead of JSON data type for database (see scripts in SqlTemplate dir). The appSettings has a new settings for it:

{
    "LockType":{"Case":"Optimistic"},
    "RefreshTimeout": 100,
    "CacheAggregateSize": 100,
    "PgSqlJsonFormat":{"Case":"PlainText"},
    "MailBoxCommandProcessorsSize": 100
}

The other option is:

    "PgSqlJsonFormat":{"Case":"PgJson"}

Basically you may wan to write json fields into text fields for various reasons (on my side I exprienced that an external library may require further tuning to properly work with jsonb fields in Postgres, so in that case a quick fix is just using text fields). Remember that we don't necessarily need Json fields as at the moment we just do serialize/deserialize and not querying on the json fields (at the moment).

• version 1.6.0: starting removing kafka for aggregates (will be replaced somehow). Use eventstore (postgres) based state viewers instead. New sample: started an example of Restaurant/Pub management. (Sample 6)

• Version 1.5.8: fix in adding events with stateId when adding more events (only the first stateId matters in adding many events, so the rest are new generated on the fly)

• Version 1.5.7:

• Added runInitAndCommand that creates a new aggregate and a command context in a single transaction.

• Changed the signature of runAggregate and runNAggregate (simplified the viewer passed as parameter avoiding a labmda)

• Version 1.5.5:

• fixed a key problem in dictionary keys in memory based eventstore (MemoryStorage). Note it is supposed to be used only for dev and testing.

• WARNING: Kafka publishing is ok but Kafka client integration needs heavy refactoring and fixing, particularly about aggregate viewer.T That means that any program that tries to build the state using KafkaStateViewer may have some inefficiencies of even errors. Just use the storage base state viewers for now (or build your own state viewers by subscribing to the Kafka topic and building the state locally). I am ready to refactor now because I have an elmish sample app for (manual) testing. An example of hot try it is by taking a look in the src/Server/server.fs in Sample4 (commented code with different ways to instantiate the "bookingsystem" sample app)

• Added SqlTempate dir with template examples for creating table relate to events and snapshots for aggregates and contexts.

• Addes sample4 witch is almost the same as sample3 but using SAFE stack (Fable/Elmish) as envelope (going to ditch sample3 because it is going to be messy)

• Version 1.5.4 Replaces version 1.5.3 (that was deprecated )

  • Aggregate snapshots added (in addition to contexts snapshots)

• Version 1.5.3 (don't use it: it is deprecated: missing packages)

• Version 1.5.1: -

  • Added a new configuration file named appSettings.json in the root of the project with the following content:

  {
      "LockType":{"Case":"Optimistic"},
      "RefreshTimeout": 100,
      "CacheAggregateSize": 100
  }

• Moreover, the specific variant of optimitic lock (classic or more permissive) can be changed by code (evenstore method). The "more permissive" optmistic lock will skip aggregate state version control so it allows that events generated in the same moment can be stored and published. Nevertheless if they end up in a violation of the invariant rule the core will skip them anyway. The more permissive optimistic lock cannot ensure that multiple aggregate transactions are handled properly: if I book seats from multiple rows it is theoretically possible that only seats from one row are booked.

• See the sql script of sample 4: it includes the steps related to change "on the fly" (by application) the db level constraints that inhibit adding two events with the same aggregate stateid.

• (in the same stream) in the event store.

• Current version 1.5.0: - Kafka integration for fine-grained aggregates (identified by Id) is included.

• Version 1.4.8: streams of events can relate to proper aggregate identified by id (and not only context). I can run commands for an arbitrary number of aggregates of some specific type. See Sample4 (booking seats of rows where rows are aggregates of a context which is a stadium). Integration with Kafka for those "fine" aggregates identified by Id is not included in this version.

• Booking seat example: https://github.com/tonyx/seatsLockWithSharpinoExample (it shows some scalability issues that will be fixed in future releases)

• Version 1.4.7: contains sample app that builds state of contexts by using Kafka subscriber (receives and processes events to build locally the state of those contexts, despite can still access the "souce of truth", which is the db/event store, when something goes wrong in processing its state, i.e. out of sync events).

• Version 1.4.6: fix bug in Postgres AddEvents

• Version 1.4.5: Upgrade to net8.0

• Info: in adding new features I may risk breaking backward compatibility. At the moment I am handling in this simple way: if I change the signature of a function I add a new function with the new signature and I deprecate the old one. I will keep the old one for a while. I will remove it only if I am sure that nobody is using it.

• Version: 1.4.4 Postgres tables of events need a new column: kafkaoffset of type BigInt. It is used to store the offset/position of the event in the Kafka topic. See the new four last alter_ Db script in Sharpino.Sample app. This feature is Not backward compatible: You need your equivalent script to update the tables of your stream of events. (Error handling can be improved in writing/reading Kafka event info there). Those data will be used in the future to feed the "kafkaViewer" on initialization. Note: kafkaoffset/kafkatopic fields on db in future versions will be unused.

• From Version 1.4.1 CommandHandler changed: runCommand requires a further parameter: todoViewer of type (stateViewer: unit → Result<EventId * 'A, string>). It can be obtained by the CommandHandler module itself.getStorageStateViewera<'A, 'E> (for database event-store based state viewer.)

• new blog post

• Version 1.4.1: little change in Kafka consumer. Can use DeliveryResults to optimize tests. Note: Kafka consumer is still in progress.

• Version 1.4.0: runCommand instead of Result<unit, string> returns, under result, info about event-store created IDs (Postgres based) of new events and eventually Kafka Delivery result (if Kafka is configured).

• Version 1.3.9: Repository interface changed (using Result type when it is needed). Note: the new Repository interface (and implementation) is not compatible with the one introduced in Version 1.3.8!

• Version 1.3.8: can use a new Repository type instead of lists (even though they are still implemented as plain lists at the moment) to handle collections of entities. Note repository is only an interface with only a plain list implementation.

• Version 1.3.5: the library is split into two nuget packages: Sharpino.Core and Sharpino.Lib. the Sharpino.Core can be included in a Shared project in the Fable Remoting style. The collections of the entities used in the Sharpino.Sample are not lists anymore but use Repository data type (which at the moment uses plain lists anyway).

• Version 1.3.4 there is the possibility to choose a pessimistic lock (or not) in command processing. Needed a configuration file named appSettings.json in the root of the project with the following content: don't use this because the configuration is changed in version 1.5.1

• this entry is ignored as the lock is always optimistic.

    "SharpinoConfig": {
        "PessimisticLock": false // or true
    }

More documentation (a little bit out of date. Will fix it soon) (Sharpino gitbook)

<a href="https://www.buymeacoffee.com/Now7pmK92m" target="_blank"><img src="https://cdn.buymeacoffee.com/buttons/v2/default-yellow.png" alt="Buy Me A Coffee" style="height: 60px !important;width: 217px !important;" ></a>