Continuing with the theme of storing data within our NativeScript application. In this exercise, we'll look at the use of the NoSQL database supported using Couchbase. So here, we will install the Couchbase Lite plugin within our NativeScript application and then store our data in a NoSQL database using the document like storage, that Couchbase provides for us. We will use this Couchbase storage for storing the favorites for our users. So, whenever the user saves any of the dishes into his or her list of favorites, the favorites information will be persistent in the Couchbase database so that even if the application is restarted or the device is restarted and app is restored, the favorites for the user will still remain and will be shown within the application. In the earlier version of the application, you saw that when you quit the application, restarted it, the favorites for the user will completely disappear. So this is where we will show how we can persist data within our application using the Couchbase database. To install the Couchbase plugin, add the prompt type, tns plugin add nativescript-couchbase. And once the plugin is installed, we switch to our application. A good pattern for us to follow is when you are using a database, create a service that takes care of all the interactions with the database and then exports an API that can be used by the other components within your application. So to do that, going to my services folder, I'm going to create a service called couchbase.service.ts file here. And in this couchbase.service.ts file, I'm going to create the couchbase.service by importing injectable from angular/core and also import couchbase from nativescript-couchbase. So the nativescript-couchbase should be in the node buttons folder and let's create the service here. So we'll say, injectable export class CouchbaseService. And in this CouchBaseService, we will declare a variable called database, which will keep a reference to our database. And then in the constructor, I'm going to create the database and then name it as 'confusion'. So, to create the database as you can see, new couchbase confusion. If this database already exists then that will be opened and we'll get a reference to it. If not, then the database will be created here. Now, for this database let's support a few methods here. So we'll support public getDocument and we will supply a document ID which is the type string for getting the document. So from the database, we'll say, return this database getDocument and pass in the docID as the parameter here. This allows us to get a document from the database. The next method that we are going to introduce is createDocument. This method takes data which is a JavaScript object or equivalently a JSON string, as the first parameter and the document identifier, as the second parameter. So, we are creating a document with a pre-specified document ID so that it's more easy for us to refer to this in our code. So, we'll say, return this database createDocument and two parameters, so that is data and docID. So this allows us to create a new document and put it into our database. If we have an existing document whose docID is already known, then we can use the updateDocument to update the document with the docID as given here. And the corresponding data again, in that form of a JavasScript object or equivalently the JSON string there. And this will be inserted into the document in place of what already exists in the document. So we'll say, return this database updateDocument and the two parameters pass in the parameters to the updateDocument method from Couchbase. And then finally, of course, we have the read, create, update, and we need the delete method. So going in, introducing public deleteDocument and specifying the docID as the parameter here, and this should delete the document with the given docID. The getDocument will return the entire document including the data that we have inserted into the document, so that we can use in our code to retrieve a document with a given docId. If the document does not exist then it will return a null. So that is what we will check for in our code. The createDocument will return the docID corresponding to that document since we already specify the docID, so that would be the same here. UpdateDocument will update the document and the delete will delete the corresponding document. With these changes, let's go ahead and now include this into our app.module.ts file so that the CouchbaseService can be used within the remaining components of our application. So importing the CouchbaseService here from services couchbase.service and then going into the providers. Let me inject the CouchbaseService here. Now, my CouchbaseService is now available for use within my application. So, going into the services in my favorites service, or recall that in the favorite's service, this is where I am providing the interface for the users to save and retrieve their favorites. So in the favorite service, I'm going to inject the CouchbaseService, so let me import the CouchbaseService in here from couchbase.service which is in the same folder. And then, I will go into the constructor. And in addition to the DishService, I will inject CouchbaseService into the constructor. Let me, next, go ahead and inject a variable called docID which I will use as the ID of the document that I saved in the Couchbase database. So they will give the stock ID as favorites. Now, within the constructor, when I start, as you see initially I have the favorites to null but if the favorites is in the database, I want to fetch that and then set that this favorites to the favorites that has been saved in the database. So right there, let me go ahead and try to find the document with this docID that we have just set up. So we will search for a document with favorites as the ID by doing getDocument. If the document exists, then the document will return. If not, this will return a null value. So if it returns a null value that means that the favorites are have not been saved into the database. So on that point, we will say, if doc equal to null, then we will create the document in the database. So, to create this document, there, I will store the favorites, is to create a JavaScript object with favorites as the property and then set that to an empty array here. Because at this moment, we don't have anything in our favorites so we'll set that to an empty array. So that is where will start out as the initial value for our favorites that is saved in our database. The second parameter of course is the docID and so that should create a document with the ID favorites in my database. If the doc already exists, so this is where we know that, that favorites has been saved into the database. So on that point, as this favorites is equal to doc, and note that we have saved the favorites in that favorites property here. So we'll say, doc.favorites and that should initialize the favorites to what is retrieved from the database. So this way, when I start out my favorite service it will be initialized with the favorites saved in the database if it exists. Otherwise, of course, that favorites is empty. So which is what we start up with and we will create the document in the database at this point. Now, whenever we modify the favorites, we want to update the favorites in our database. So the two places where we will do the modification is in the add favorite and the delete favorite. So, going to the add favorite method here, right there, we are modifying the favorite. So, at this point, I will save it to the Couchbase by saying, this Couchbase updateDocument and the first parameter is the docID that I have already initialized earlier. And the second parameter, of course, is the JavaScript object with the property favorites just like we used earlier. But here, the second value would be the current value of the favorites. So notice that we are saving the updated value of favorites into our database. So this is how we will persist the change that we make to the favorites. So this is where we are making a change to favorites by adding the new one to the favorites. And then, this is where we will persist that change to our database. I need to do exactly the same operation also in my delete favorites. So going to the delete favorites, notice that right there we are modifying the favorites here by splicing out the item, the index from the favorite. So right there, also I need to save the changes into the database. So that is where I will do this CouchbaseService updateDocument and update the current favorites that is saved in my Couchbase. That's it. Let's save all the changes and then go and take a look at our application. My app did not get reinstalled. Sometimes this happens, in that case, I'm just restarting the tns run android one more time to redeploy the application onto the device. So if anytime your app doesn't automatically update, just relaunch the tns run android, and the app should automatically update itself. So when my app is now ready, I'm going to first demonstrate to you that my favorites is currently empty. Nothing exists there. So let's go to our dishes and then add a couple to my favorites. So let me add in, this dish to my favorites and also going to the second one. For the second dish, bring up the action dialogue and click on add to favorites and that should also add into the favorites. So this, you should have done as part of your second assignment. So now, we have two dishes in our favorites. Then we go and check our favorites. You'll notice that now there are two dishes in our favorites. Let me close the application, so I'm going to close the application and then we'll restart the application. When you now bring up my favorites, you would notice that my favorites what I have saved will still persist in my application. So even if I restart my application, even if I restart my device, the list of favorites that I've saved will always be there within my application and will be brought up whenever I go to my list of favorites. Now, after this point, you will have to explicitly delete your favorites if you don't want them to be in your list of favorites. Because, even if you restart your application, the favorites will still be displayed in the list of favorites. So, you see how we can use the Couchbase to persist our favorites data within our application. With this, we complete this exercise. In this exercise, we have seen how we can use Couchbase within our application. This is a good time for you to do a get comment with the message storage with Couchbase.
