Practical Microservices

Adding Validation to a Component

Let’s handle that NameVideo command in the video-publishing Component:

video-tutorials/src/components/video-publishing/index.js

function createHandlers ({ messageStore }) {
  return {
    NameVideo: command => {
      const context = { 
        command: command,
        messageStore: messageStore
      }

      return Bluebird.resolve(context)
        .then(loadVideo) 
        .then(ensureCommandHasNotBeenProcessed)
        .then(ensureNameIsValid)
        .then(writeVideoNamedEvent)
        .catch(CommandAlreadyProcessedError, () => {}) 
        .catch( 
          ValidationError,
          err => writeVideoNameRejectedEvent(context, err.message)
        )
    },
    // ...
  }
}

​①​

First, build a context consisting of the command in question and the messageStore.

​②​