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    Manage Data in the ngrx Store through a Reducer in Angular

    Lukas RuebbelkeLukas Ruebbelke
    angularAngular
    ^7.0.3
    ngrx-store@ngrx/store

    The ngrx store is responsible for storing application state while the reducer is responsible for managing how it that state manipulated. In this lesson, we are going to build out the feature reducer to handle basic operations like select, create, update, and delete. We will discuss how actions flow into a reducer and how operations in the reducer must be immutable. From there, we will replace the service calls within our feature component to dispatch the equivalent action objects for consumption within our reducer.

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    Transcript

    Transcript

    Now that we have our basic reducer defined, let's go ahead and start to flesh this out so that it can perform meaningful units of work. Right now we have a default switch case where we are returning the state as it is at any given time. This is considered just a fallback for if there is not a match between the action type and the available case statements.

    To flesh this out, let's hop into the switch statement, and let's start to build out some of the available cases that we would want. For instance, let's do a select case, then we could do create. We could also do update and as well delete. So we are, for the most part, covering most of the crud operations, and then, within these cases, we are going to perform a specific unit of work for that specific action type.

    Every one of these operations, they are going to be immutable by nature, and so, for instance, in the select case, we are going to just return a new object. Using an object literal will define selected project ID, and then we'll pull the payload off of the action objects. Actions typically have a type and a payload property, and so we're just going to set a new selected project ID, and then we'll set projects to whatever the projects were.

    That is going to remain unchanged. For the create update and delete operations, this is going to be slightly different as we're not dealing with the selected project ID but rather we're dealing with the project's collection. So I'll do a new object literal and from selected project ID, I'm just going to set it to the existing selected project ID off of state.

    From our projects, I'm going to copy this, and I'm going to paste the structure into create, update and delete, because they're going to be exactly the same in every one of these cases up to this ppoint. Let me just clean this up real quick, and then from here we need to do some sort of manipulation.

    Now, remember we need to use immutable operations so I have these helper functions, create project, update project, delete project that, in this case, create project is just concatenating a project onto the existing array. Update project is just mapping over and filtering or mapping over and assigning a new object to the one that we want to update. Delete project is just filtering out the project that we want to delete.

    These are just some helper functions that I've provided, that are immutable in nature. Let's go ahead and in our create case, we'll call create project, and we'll pass in state.projects, and then the project we want to add, which is under action.payload.

    We'll go ahead and do the same thing for update. This is going to be update project. It's going to take state.projects as well as the action payload.

    One of the things I enjoy about NgRx is that it's very conventional. And so delete project. We're going to also send in state.projects in the action payload, so you can see this consistency across your application. Depending on select create, update or delete, that it takes in state and then, based on the action type, it would perform some immutable operations such as create, update or delete.

    Now that we have filled this reducer out for the operations that we want, it's time to go into our projects feature and start to communicate or intent or issue a command into the reducer for this work to be done. If we go into the bottom of this, you can see that we have these service calls that are happening, and we are going to just get rid of these.

    Let's copy out just some of the guts here, and this will eventually go away, but for now we still want to keep this. And so we'll just paste this into the bottom of the other two methods. Then from here, once we've kind of updated these to be appropriately descriptive, we're going to go through and replace these service calls.

    We can get rid of this project.service.create call. Instead we are going to dispatch an action object. So this is the first time we've seen this, but we're going to call this .store, and we're going to dispatch, in this case, just a simple object literal that's going to have two properties.

    We can kind of infer this from the reducer that we've been working with as a type and a payload property. Type is create and then the payload is the project we want to create.

    Now let's go ahead and do the same thing for update. So this store dispatch, we're going to pass in an appropriate action object which is going to be type update, also passing in the payload. This is how you communicate to a reducer is via an action object. Once it's dispatched, then the reducer will pick that up, then, based on the action type, perform some operation.

    We'll go ahead and do this for delete as well. So type is delete and then we'll pass in the project payload as well.

    Let's hop into our browser and let's see if this is working. So we'll go over here. Let's go ahead and we will change this and then update it. And as you can see now, we're basically just manipulating this collection in memory.

    Let's go ahead and create a new project. We'll just give it a big holla, fill this out here real quick, and then we'll go save. You can see now that we're dispatching that action, and then it's going and heading our reducer, and then adding that to the project's collection.

    Quick review -- all we've done is we've defined cases within our switch block to handle that unit of work that, based on the action type, that then returns a new object that is either updating the project ID or the projects itself using the helper functions that I have defined.

    So this is incoming, that we have an action object coming in, and we're performing some operation. Then within the application itself, we are going to dispatch these action objects, which in this case for now, is just a very simple object literal that has a type and a payload property. This is how you flesh out a reducer within your application.