The traditional application | laravel-event-sourcing | Spatie SPATIE Laravel Event Sourcing ========================= spatie.be/open-source [Docs](https://spatie.be/docs) [Laravel-event-sourcing](https://spatie.be/docs/laravel-event-sourcing/v3) Getting-familiar-with-event-sourcing The traditional application Version v7 v6 v5 v4 v3 v2 v1 Other versions for crawler [v7](https://spatie.be/docs/laravel-event-sourcing/v7) [v6](https://spatie.be/docs/laravel-event-sourcing/v6) [v5](https://spatie.be/docs/laravel-event-sourcing/v5) [v4](https://spatie.be/docs/laravel-event-sourcing/v4) [v3](https://spatie.be/docs/laravel-event-sourcing/v3) [v2](https://spatie.be/docs/laravel-event-sourcing/v2) [v1](https://spatie.be/docs/laravel-event-sourcing/v1) - [ Introduction ](https://spatie.be/docs/laravel-event-sourcing/v3/introduction) - [ Support us ](https://spatie.be/docs/laravel-event-sourcing/v3/support-us) - [ Requirements ](https://spatie.be/docs/laravel-event-sourcing/v3/requirements) - [ Installation & setup ](https://spatie.be/docs/laravel-event-sourcing/v3/installation-setup) - [ Questions and issues ](https://spatie.be/docs/laravel-event-sourcing/v3/questions-issues) - [ Changelog ](https://spatie.be/docs/laravel-event-sourcing/v3/changelog) - [ Upgrading ](https://spatie.be/docs/laravel-event-sourcing/v3/upgrading) - [ Resources and alternatives ](https://spatie.be/docs/laravel-event-sourcing/v3/resources-and-alternatives) - [ About us ](https://spatie.be/docs/laravel-event-sourcing/v3/about-us) Getting familiar with event sourcing ------------------------------------ - [ Introduction ](https://spatie.be/docs/laravel-event-sourcing/v3/getting-familiar-with-event-sourcing/introduction) - [ The traditional application ](https://spatie.be/docs/laravel-event-sourcing/v3/getting-familiar-with-event-sourcing/the-traditional-application) - [ Using projectors to transform events ](https://spatie.be/docs/laravel-event-sourcing/v3/getting-familiar-with-event-sourcing/using-projectors-to-transform-events) - [ Using aggregates to make decisions based on the past ](https://spatie.be/docs/laravel-event-sourcing/v3/getting-familiar-with-event-sourcing/using-aggregates-to-make-decisions-based-on-the-past) Using projectors ---------------- - [ Writing your first projector ](https://spatie.be/docs/laravel-event-sourcing/v3/using-projectors/writing-your-first-projector) - [ Creating and registering projectors ](https://spatie.be/docs/laravel-event-sourcing/v3/using-projectors/creating-and-configuring-projectors) - [ Making sure events get handled in the right order ](https://spatie.be/docs/laravel-event-sourcing/v3/using-projectors/making-sure-events-get-handled-in-the-right-order) - [ Thinking in events ](https://spatie.be/docs/laravel-event-sourcing/v3/using-projectors/thinking-in-events) Using reactors -------------- - [ Writing your first reactor ](https://spatie.be/docs/laravel-event-sourcing/v3/using-reactors/writing-your-first-reactor) - [ Creating and configuring reactors ](https://spatie.be/docs/laravel-event-sourcing/v3/using-reactors/creating-and-configuring-reactors) Using aggregates ---------------- - [ Writing your first aggregate ](https://spatie.be/docs/laravel-event-sourcing/v3/using-aggregates/writing-your-first-aggregate) - [ Creating and configuring aggregates ](https://spatie.be/docs/laravel-event-sourcing/v3/using-aggregates/creating-and-configuring-aggregates) - [ Testing aggregates ](https://spatie.be/docs/laravel-event-sourcing/v3/using-aggregates/testing-aggregates) - [ Snapshots ](https://spatie.be/docs/laravel-event-sourcing/v3/using-aggregates/snapshots) Advanced usage -------------- - [ Preparing events ](https://spatie.be/docs/laravel-event-sourcing/v3/advanced-usage/preparing-events) - [ Replaying events ](https://spatie.be/docs/laravel-event-sourcing/v3/advanced-usage/replaying-events) - [ Storing metadata ](https://spatie.be/docs/laravel-event-sourcing/v3/advanced-usage/storing-metadata) - [ Handling exceptions ](https://spatie.be/docs/laravel-event-sourcing/v3/advanced-usage/handling-exceptions) - [ Discovering projectors and reactors ](https://spatie.be/docs/laravel-event-sourcing/v3/advanced-usage/discovering-projectors-and-reactors) - [ Using your own event storage model ](https://spatie.be/docs/laravel-event-sourcing/v3/advanced-usage/using-your-own-event-storage-model) - [ Using your own event storage repository ](https://spatie.be/docs/laravel-event-sourcing/v3/advanced-usage/using-your-own-event-storage-repository) - [ Using your own event serializer ](https://spatie.be/docs/laravel-event-sourcing/v3/advanced-usage/using-your-own-event-serializer) - [ Using aliases for stored event classes ](https://spatie.be/docs/laravel-event-sourcing/v3/advanced-usage/using-aliases-for-stored-event-classes) - [ Adding and Removing Projectors and Reactors ](https://spatie.be/docs/laravel-event-sourcing/v3/advanced-usage/adding-and-removing-projectors-and-reactors) - [ Allowing concurrent persists ](https://spatie.be/docs/laravel-event-sourcing/v3/advanced-usage/allowing-concurrent-persists) You are viewing the documentation for **an older version** of this package. You can check the version you are using with the following command: ` composer show spatie/laravel-event-sourcing ` The traditional application =========================== In a traditional application, you're probably going to use a database to hold the state of your application. Whenever you want to update a state, you're simply going to overwrite the old value. That old value isn't accessible anymore. Your application only holds the current state. You might think that you still have the old state inside your backups. But they don't count. Your app probably can't, nor should it, make decisions on data inside those backups. First, we write value X ![](/docs/laravel-event-sourcing/v3/images/db-01.svg) Next, we overwrite X by Y. X cannot be accessed anymore. ![](/docs/laravel-event-sourcing/v3/images/db-02.svg)Here's a demo application that uses a traditional architecture. Inside the [`AccountsController`](https://github.com/spatie/larabank-traditional/blob/9cc38858c50a4f2ac5a36e64719c891fac85bd3f/app/Http/Controllers/AccountsController.php) we are just going to [create new accounts](https://github.com/spatie/larabank-traditional/blob/9cc38858c50a4f2ac5a36e64719c891fac85bd3f/app/Http/Controllers/AccountsController.php#L19-L27) and [update the balance](https://github.com/spatie/larabank-traditional/blob/9cc38858c50a4f2ac5a36e64719c891fac85bd3f/app/Http/Controllers/AccountsController.php#L29-L36). We're using an eloquent model to update the database. Whenever we change the balance of the account, the old value is lost.