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Let's take a look at the solution we're going to use to actually persist our list of cells back to our

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API.

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So we're going to create a save cells middleware.

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This nowhere's job is going to be to watch for actions that get dispatched to have a type of mousel

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update cell, insert cell after and delete cell.

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Remember, these are all the different action types that can somehow modify the list of cells that are

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stored inside of our cells reducer.

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So when we start thinking about saving our list of cells, whenever something changes, well, these

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are the only things that can actually cause a change.

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So if our middleware ever sees one of these actions, that is a sign that our list of cells is about

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to change.

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So we're going to take that action, forward it onto our store, and then immediately after, we're

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going to try to persist our list of cells using the safe cells.

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Action creator we just put together.

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This diagram is a little bit deceptively simple.

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It turns out there are going to be one or two really interesting things we need to think about as we

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put this middleware together.

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But right now, let's just start to write out the middleware and then just kind of encounter these little

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problems in turn.

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OK, so back inside my code editor, I'm going to find my state directory.

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Inside there will make a new folder called Middlebury's.

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And then inside of that, I'll make a new file and I'm going to call this persist middleware instead

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of save cells just to have a name that is different than that action creator.

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So I will call this persist middleware dot.

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It's not the best name, but good enough will deal with it.

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In general, I'm going to assume that you are familiar with Redox Middlebury's if you're not totally

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fine, just type along and you'll get pretty familiar with what's going on here pretty quickly.

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The first thing I want to remind you in general around Middlebury's is that, remember, they've got

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that really weird function signature.

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So we're going to define and export a function called persist middleware.

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And here's where things get weird, remember, a middleware is a function that returns, a function

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that returns a function.

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So this is why medal winners are just a little bit nasty.

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And then remember, each of these different functions get called with a slightly different argument.

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So the first one is going to be called with not exactly our Redux store, but it's frequently abbreviated

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and just called store.

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So this is not exactly our store, like our entire Redock store, but it is an object that is very similar.

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Then the second function is going to be called with our next function, which is how we take an action

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and for it along to the next middleware, where all of our different reducers and then finally the innermost

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function receives our action.

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So that's going to be the action that we want to take a look at and determine whether it is the Mousel

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update sell, blah, blah, blah, all those different action types.

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And right away, we do have to apply a couple of different type annotations to each of these different

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functions.

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On this store right here, the only thing that we really care about on the entire store object is dispatch.

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It's going to structure off just dispatch, and I'm going to annotate it in the same way that we've

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annotated the dispatch function inside of our different action creators.

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So I'm going to put in this is an object with a dispatch property.

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That is of type dispatch.

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And then put in action like so.

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I'm then going to make sure that I immediately import dispatch and action from the appropriate sources

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at the top, so I will import dispatch.

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From Redux.

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And action from up on directory actions.

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Next up, our next function, this is a function that is going to be called with some action that we

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want to put it on so we can just annotate this type manually.

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We can say that this will be a function.

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They'll be called with something that will call action, and it's going to be of type action.

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And I don't expect to return anything, so I'm going to put in a return type invitation avoid.

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Then finally, our innermost function right here is going to receive some action, which once again

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is just going to be of type action.

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OK, so now we can start to put together some implementation.

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The first thing we have to do is decide whether or not that incoming action has a type of one of these

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types.

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So we better import our action type in at the top so we can actually do some comparison.

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Up here will do import action type.

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From up on directory action type's.

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Then inside of our middleware itself, we receive on those action types, we want to dispatch that action

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creator of save cells.

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So let's make sure we also import that action to right away as well.

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So I'll get.

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Save cells from up on directory action creators.

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So then inside of our innermost function right here, the first thing we want to do is take whatever

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incoming action is flowing into our middleware and no matter what, we want to pass it on to the next

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middleware on our chain.

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We're not trying to stop or modify any actions here.

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We're trying to pass along every single action that we receive.

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The only exception is that we if we receive one of these actions, we want to dispatch an additional

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action as well.

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So I'm going to put in here next with action right away, because, again, no matter what, we always

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want to it on every single action.

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Now, at this point, let's just save this file as is and wired up to our Redock store and make sure

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that everything works as expected with just this very small amount of code we have.

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So I'm going to go back over to my Staats file.

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Inside of here at the very top, I'm going to import the fiercest middleware.

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We just put together.

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Middleware is persist middleware.

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And then I'm going to wired up to our applied middleware call, we can put this new middleware before

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or after Redux Thunk it doesn't make a difference in this case.

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So either location just fine.

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Let's then save this.

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Go back over to our application, do a quick refresh, and we should still see everything working as

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expected.

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I should still be able to change the contents of a cell, add a new cell in, or do whatever else I

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want to do.

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Looks like everything is still good.

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So let's take a pause right here and then continue working on our middleware in just a moment.