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    Cache Data from TCP/IP Connections with IndexedDB


    sw-precache caches nicely both static assets and external resources. But real time systems, such as Firebase or, work on TCP/IP.

    In this lesson I’ll show you how you can use IndexedDB in order to cache the data coming from Firebase.



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    Instructor: When we click on any match, we're going to a detail view where we can write a message. This detail view is in the detail component. In here, we're using a Firebase stream to synchronize a method as a state with the Firebase database.

    These messages are not cached because Firebase works through TCP circuits. They cannot be cached, neither by static caching or run time caching, so we have to do the caching ourselves. For that, we have several options. While local storage and session storage or synchronous storages, IndexedDB is asynchronous, which makes it perfect to cache the messages without blocking the UA.

    Let's start by opening a terminal and install idb-keyval. Then let's create, under the src folder, a store.js Here, let's import idb-keyval from idb-keyval. IndexedDB is somewhat complex, and it's not the scope of this lesson, but idb-keyval allow us to use it with a simplified API, similar to the local storage or session storage by using a key value storage.

    This module should have a get method with states and ID, and then it calls the get method of idb-keyval. It will have, as well, a save method that will take an ID and messages. It will call the send method of idb-keyval, passing the ID and the messages. Don't forget to support these functions.

    Then let's go to the detail view, and I start by defining the data option for the component state, which has a cache messages property inaudible to a empty array. Since we are going to use a computed property with the name of messages, let's rename this one to fireMessages.

    Now let's create that computed property, so messages and this property will check that we have fireMessages by checking the length. Then, it will return the fireMessages, but if not, it will return the cached messages. If you think about it, we are using a work-first approach. We check that we have fireMessages, which will mean we have the connection open. If not, it will load the cached messages.

    In order to interact with the IndexedDB, let's import the getUnsaved methods from our store, and then let's create a created hook. In here, we'll get the cached messages for the ID of this picture, and IndexedDB returns a promise in the case of using IDB. Let's use them to get the messages, and then we'll set the cached messages to those messages.

    We're still not saving the messages to into IndexedDB. For that, an easy way is by using the watch install method of Vue, so we watch over the messages in the way that, when they change, we'll save them using the ID and passing the messages.

    In this case, we have to specify deep true as the option for the watch method. Otherwise, the messages array will be watched only by reference, which means that if we add a message to the array it will not change. By using deep true, it will be deeply watched.

    Finally, if we run this and go the images, let's open up an image and write something. If we go and turn off the Internet, we reload it, the messages are still there. Of course, if we try to send now a message, it will break, because we have no Internet. We'll take care of that later.

    You can inspect your IndexedDB storage by opening the dev tools. In the application tab, you have an IndexedDB entry in the storage section. We can click in the keyval, and we see and entry with the key two and an array of one, which is this message. The IndexedDB storage capacity is quite high, but be careful and set a limit on what data you store.