Question: Where to put business logic / validations?

[arunoda]

I'm right now learning Redux. So, I'm looking for some places where we can put business logic and validations.

The App

It's a simple counter. And the counter value must be sit between 1-5. I has no idea on where to put my app's business logic. So, this is what I did.

Inside Reducers

When there is no server side async stuff, I put my validations inside the reducer like this.
See: https://github.com/arunoda/learn-redux/blob/dir-structure/src/reducers/index.js#L6
It worked pretty well.

Inside Action Creators

When I need to sync the store with the server, I used redux-thunk. Now I had to validate in the action creators as well. So, instead of validating in the reducers, I moved validation logic into the action creators. See: https://goo.gl/VC8lmp

So, I think it's best to put validation/business logic into action creators, specially with redux-thunk. (where I can get the store state easily). Is this the pattern used normally, or is there any better approaches?

[dvdzkwsk]

I've had good success following the pattern mentioned in the docs, which is exactly what you describe with redux-thunk. Perhaps there are things that I'm missing out on, but it works especially well for operations such as only making a request if the redux cache is stale.

From: http://rackt.org/redux/docs/advanced/ExampleRedditAPI.html

function shouldFetchPosts(state, reddit) {
  const posts = state.postsByReddit[reddit]
  if (!posts) {
    return true
  } else if (posts.isFetching) {
    return false
  } else {
    return posts.didInvalidate
  }
}

export function fetchPostsIfNeeded(reddit) {
  return (dispatch, getState) => {
    if (shouldFetchPosts(getState(), reddit)) {
      return dispatch(fetchPosts(reddit))
    }
  }
}

[arunoda]

Thanks. I followed exactly something like this.
We' can close this issue now.

[ColCh]

@arunoda @davezuko why not using Smart components for it? Looks pretty good.

[sompylasar]

@ColCh Because "smart" (actually, "container") components are just thin wrappers that connect other views to the model (which in Redux is the reducer, and action creator thunks), but business logic should be in the model.

[gkrinc]

So is the consensus that business logic should exist in the action creators?

[markerikson]

It's reasonable to put it in both action creators and reducers, depending on your setup and how you want to divide things. See the answer on this topic in the Redux FAQ: http://redux.js.org/docs/FAQ.html#structure-business-logic .

[ezhikov]

Did put my logic to specific middleware. Not sure, if it is "best practices", but works well by now.

[zdila]

https://medium.com/@jeffbski/where-do-i-put-my-business-logic-in-a-react-redux-application-9253ef91ce1#.z49ah1act

[steodor]

How about in a redux-saga? It's overkill in simple cases but if you have to manage multiple sync and async validations and/or have a flow like validate these fields only if the previous async validation succeded etc., then it becomes a viable solution.

[kiss90benedek]

@markerikson the URL is now http://redux.js.org/docs/faq/CodeStructure.html#structure-business-logic

[Vanuan]

There's a third option: middleware + dedicated business logic objects:

// call it when needed (e.g. componentDidMount)
dispatch({ type: 'BUSINESS_ACTION', name: 'showSomethingUseful', params: { entityId: props.match.entityId } });

// call it in middleware
handlers[action.name]({ store, webApi, params: action.params });

// when it's called:
handlers = {
  'showSomethingUseful': async ({ store, webApi, params }) => {
    // show some spinners
    store.dispatch({ loading: true });
    try {
      // load some data
      const data = await webApi.load(params.entityId);
      // do some business logic
      const logic = new Logic(data);
      const displayFields = { field: logic.calculateSomething() };
      // display some data
      store.dispatch({ loading: false, data: displayFields });
    } catch(e) {
      // display some errors
      store.dispatch({ loading: false, error: e });
    }
  }
}

Here we divide our state into "UI" state and "Business" state. UI state is things like routes, client side filtering, menus opened, forms filled, options selected, etc. Business state is data from db along with calculated fields, errors, loading state and validation messages.

UI state is kept in redux store, while business state is calculated on the fly + some caching mechanism implemented in web api client.

Any feedback on such approach? Is it against the functional approach? Any caveats?