Understanding DDD and CQRS: Utilizing Multiple Repositories in a Single Command Handler
Discover effective strategies for handling multiple repositories in Domain-Driven Design (DDD) and Command Query Responsibility Segregation (CQRS) during e-shop checkout processes.
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This video is based on the question https://stackoverflow.com/q/69690198/ asked by the user 'CKK' ( https://stackoverflow.com/u/10705906/ ) and on the answer https://stackoverflow.com/a/69692586/ provided by the user 'Neil W' ( https://stackoverflow.com/u/2936204/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.
Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: DDD and CQRS: use multiple repositories from a single command handler?
Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/licensing
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/by-sa/4.0/ ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/by-sa/4.0/ ) license.
If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
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Understanding DDD and CQRS: Utilizing Multiple Repositories in a Single Command Handler
When developing an e-commerce application, one of the key challenges developers face is managing the flow of commands and ensuring data consistency during complex operations, such as processing a customer's checkout. This is especially true when using design patterns like Domain-Driven Design (DDD) and Command Query Responsibility Segregation (CQRS). A practical scenario to explore this challenge is the "Create Order" process in an e-shop, where multiple repositories may be involved. Let's delve into the problem and outline effective solutions.
The Problem: Creating an Order and Managing Inventory
Imagine a situation where a user adds items to their cart and decides to check out. The action triggers the issuance of a "Create Order" command. However, before creating an order record, several actions must take place:
Check if the items are still available.
Reserve the items to prevent stock from being sold to other customers during the checkout process.
This leads to a vital question: How can we implement this "check and reserve" routine effectively while adhering to the principles of DDD and CQRS? Here are some potential approaches:
Using Multiple Repositories in a Single Command Handler: Directly invoke both ProductStockRepository to reserve items and OrderRepository to create the order within the same command handler.
Abstracting Repository Calls: Instead of interacting with ProductStockRepository directly in the command handler, create a ProductStockService to manage these operations more cleanly.
Implementing an Internal Command: Dispatch a "Reserve Products" command within the "Create Order" handler to handle the reservation separately.
Splitting Command Actions: Have the frontend send a "Reserve Products" command initially, which then triggers an event to create the order once the reservation is confirmed.
To find the most appropriate approach, we need to consider whether the reservation and order processes reside within the same bounded context (BC) or different ones.
The Solution: Approaches Based on Context
1. Reservation and Order in the Same Bounded Context
If both operations exist within the same bounded context, here are three detailed options to implement them:
Option 1: Using a Domain Service
The CreateOrderCommand is dispatched.
A transaction is started at the infrastructure level.
The command handler invokes the CreateOrderDomainService.
This service retrieves products and reserves them, throwing an error if it fails.
It then attempts to create the order and save it to the repository.
If everything succeeds, the transaction is committed; otherwise, it is aborted.
Option 2: Employing Domain Events
The CreateOrderCommand initializes the process.
The command handler creates the order and triggers an OrderCreated domain event.
An event handler listens for the OrderCreated event and handles the reservation of products.
Transaction management is similar: commit on success, abort on failure.
Option 3: Injecting Products into the Order
The command prints a dispatch.
In the command handler, retrieve the products and pass them into the order being created.
The order then attempts to reserve these products directly and throws an error if it cannot.
Again, transaction success leads to commitment; otherwise, it aborts.
2. Reservation and Order in Different Bounded Contexts
If these processes exist in separate bounded contexts, we can take a more distributed approach:
Option 1: Using a Domain Service Across Boundaries
The CreateOrderCommand is dispatched.
Start a transaction in the infrastructure.
The command ha
Видео Understanding DDD and CQRS: Utilizing Multiple Repositories in a Single Command Handler канала vlogize
---
This video is based on the question https://stackoverflow.com/q/69690198/ asked by the user 'CKK' ( https://stackoverflow.com/u/10705906/ ) and on the answer https://stackoverflow.com/a/69692586/ provided by the user 'Neil W' ( https://stackoverflow.com/u/2936204/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.
Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: DDD and CQRS: use multiple repositories from a single command handler?
Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/licensing
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/by-sa/4.0/ ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/by-sa/4.0/ ) license.
If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding DDD and CQRS: Utilizing Multiple Repositories in a Single Command Handler
When developing an e-commerce application, one of the key challenges developers face is managing the flow of commands and ensuring data consistency during complex operations, such as processing a customer's checkout. This is especially true when using design patterns like Domain-Driven Design (DDD) and Command Query Responsibility Segregation (CQRS). A practical scenario to explore this challenge is the "Create Order" process in an e-shop, where multiple repositories may be involved. Let's delve into the problem and outline effective solutions.
The Problem: Creating an Order and Managing Inventory
Imagine a situation where a user adds items to their cart and decides to check out. The action triggers the issuance of a "Create Order" command. However, before creating an order record, several actions must take place:
Check if the items are still available.
Reserve the items to prevent stock from being sold to other customers during the checkout process.
This leads to a vital question: How can we implement this "check and reserve" routine effectively while adhering to the principles of DDD and CQRS? Here are some potential approaches:
Using Multiple Repositories in a Single Command Handler: Directly invoke both ProductStockRepository to reserve items and OrderRepository to create the order within the same command handler.
Abstracting Repository Calls: Instead of interacting with ProductStockRepository directly in the command handler, create a ProductStockService to manage these operations more cleanly.
Implementing an Internal Command: Dispatch a "Reserve Products" command within the "Create Order" handler to handle the reservation separately.
Splitting Command Actions: Have the frontend send a "Reserve Products" command initially, which then triggers an event to create the order once the reservation is confirmed.
To find the most appropriate approach, we need to consider whether the reservation and order processes reside within the same bounded context (BC) or different ones.
The Solution: Approaches Based on Context
1. Reservation and Order in the Same Bounded Context
If both operations exist within the same bounded context, here are three detailed options to implement them:
Option 1: Using a Domain Service
The CreateOrderCommand is dispatched.
A transaction is started at the infrastructure level.
The command handler invokes the CreateOrderDomainService.
This service retrieves products and reserves them, throwing an error if it fails.
It then attempts to create the order and save it to the repository.
If everything succeeds, the transaction is committed; otherwise, it is aborted.
Option 2: Employing Domain Events
The CreateOrderCommand initializes the process.
The command handler creates the order and triggers an OrderCreated domain event.
An event handler listens for the OrderCreated event and handles the reservation of products.
Transaction management is similar: commit on success, abort on failure.
Option 3: Injecting Products into the Order
The command prints a dispatch.
In the command handler, retrieve the products and pass them into the order being created.
The order then attempts to reserve these products directly and throws an error if it cannot.
Again, transaction success leads to commitment; otherwise, it aborts.
2. Reservation and Order in Different Bounded Contexts
If these processes exist in separate bounded contexts, we can take a more distributed approach:
Option 1: Using a Domain Service Across Boundaries
The CreateOrderCommand is dispatched.
Start a transaction in the infrastructure.
The command ha
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