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Simple CQRS example
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Latest commit b521257 Dec 2, 2013

m-r (RESTful)

This prototype exposes Greg Young's m-r sample - which has arguably been the de-facto CRQS + ES (ES = Event Sourcing) sample in the community - through a RESTful interface. While in CQRS commands and queries live in disparate systems, they will be represented as a unified resource at the API Layer.

This prototype exemplifies:

  • Forming the API's Public Domain abstracing Server/BoundedCountext's internal domain. Public domain is composed of DTOs and commands.
  • Service has been exposed as resources. Resource accept GET, POST, DELETE and PUT requests - currently OPTIONS is not implemented.
    • GET /api/InventoryItem [gets all items]
    • GET /api/InventoryItem/{id} [gets detail of a single item]
    • POST /api/InventoryItem [creates an item]
    • POST /api/InventoryItem/{id}* [checks in stock items to the inventory]
    • POST /api/InventoryItem/{id}* [removes stock items from the inventory]
    • PUT /api/InventoryItem/{id} [renames an item]
    • DELETE /api/InventoryItem/{id} [de-activates an item]
  • Operations marked with the * above require passing the command type as described by the 5 levels of media type. This helps to avoid RPC-style URLs where a verb is defined on the top of a resource: so instead of /api/InventoryItem/{id}/AddToStock, we send a request with media type application/json;domain-model=CheckInItemsToInventoryCommand. This also moves away from the common misconception that HTTP Verbs must be mapped to CRUD.
  • Exposing ES concurrency through HTTP's ETag and If-Match and If-None-Match conditional PUT and GET requests.
  • Enabling caching on the top of single resources and returning 304 for resources that are not modified. Also returning 412 (PreconditionFailed) on unsuccessful If-Match conditional PUT calls.
  • As per RFC 2616, ETag has been opacified so that the client cannot guess the values - this would have been possible if we had exposed version numbers directly.
  • Other HTTP-level semantics such as status codes, populating Location header after POST, etc.
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