NgRx-针对商店的减速器优先级和执行顺序

Question

If different reducers are associated to the same action and are performing changes to the store, are they receiving the same version of it before any edit happens? Is there a priority to consider?

Example:

Lets assume you dispatch an action Update to edit an entity on server side, once data is successfully updated, an effect will dispatch an Update_Success action with an instance of the newly received version of entity as payload. A first classic and logical reducer will use it to update the store:

case ItemActionTypes.UPDATE_ITEM_SUCCESS: {
    const item = action.payload;

    return {
    ...adapter.upsertOne(item, state),
    loaded: true,
    loading: false
    };
}

Now lets assume that in a different file, you have a different reducer associated to the same action and needs to compare the newly received entity against the old one in store:

case ItemActionTypes.UPDATE_ITEM_SUCCESS: {
    const item = action.payload;
    const oldItem = state.entities[item.id];
    const changes = getAffectedProperties(item, oldItem);

    // ...
}

The question is: Is there any chance oldItem is actually holding the newly received item instead of the old one as the first reducer may have already updated it? Is it a first come first serve case? or is there anything on its implementation that guarantees all reducers are performing changes to the the same version of the store and maybe merging those changes at a further step?

Answer 1

If different reducers are associated to the same action and are performing changes to the store, are they receiving the same version of it before any edit happens? Is there a priority to consider?

Reducers only have access to their piece of state. So you're not supposed to really care about that.

Also, when one action is dispatched, all the reducers are called in a synchronous way. Which means that if for the ACTION_A you're modifying your store from different places (/ different reducers), your selectors (or even the view), will only be refreshed once. When all the updates for that action are applied on the store.