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  <section id="intro">
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    <p>
      After reading this tutorial you will know how to create full-stack apps using MEAN stack.
    </p>
  </section>

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  <section id="whatis-mean">
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    <h2 class="mb-4">What does MEAN stand for?</h2>

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        <p>
          <strong>MEAN</strong> is an acronym for web development tech stack consisting of these
          four technologies:
        </p>
        <ul>
          <li><strong>M</strong>ongoDB</li>
          <li><strong>E</strong>xpress.js</li>
          <li><strong>A</strong>ngular</li>
          <li><strong>N</strong>ode.js</li>
        </ul>

        <p>Let's quickly recall what are these.</p>
      </div>
    </div>
  </section>

  <section id="mean-recap">
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    <h2 class="mb-4">MEAN recap</h2>

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        <p>Here's a quick recap what are the main technologies used in the MEAN stack:</p>
        <ul>
          <li>
            <strong>MongoDB</strong> is a document-oriented NoSQL database meant to store
            non-tabular data. If you want to learn more about it check out a
            <a href="/docs/standard/cli/getting-started/mongo/" target="_blank">separate tutorial</a
            >.
          </li>
          <li>
            <strong>Express.js</strong> is a web framework built for Node.js that allows you to
            create web servers in a very convenient way. Learn more about it
            <a href="https://mdbootstrap.com/docs/standard/cli/getting-started/express/">here</a>.
          </li>
          <li>
            <strong>Angular</strong> is a JavaScript framework that allows you to create very
            advanced single-page apps. You can check out how to create an Angular project in
            <a href="/docs/standard/cli/getting-started/angular/">another tutorial</a>.
          </li>
          <li>
            <strong>Node.js</strong> is a multi-platform JavaScript runtime built on V8 engine. It's
            used as a backend side of web apps. Read more about it
            <a href="https://mdbgo.com/docs/tutorials/node/">here</a>.
          </li>
        </ul>

        <p>
          We won't dive deep into details about how to get started with these technologies using MDB
          GO. Go ahead and check the linked tutorials and once you learn a few things get back here.
        </p>
        <p>If you have enough knowledge to get started, let's do this.</p>
      </div>
    </div>
  </section>

  <section id="building-mean-app">
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    <h2 class="mb-4">Building the MEAN app</h2>

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        <p>
          Our example app will be a TODO list. It's a very popular use-case so let's simply get
          things done one at a time. We will go through the following steps:
        </p>
        <ul>
          <li>Create a MongoDB database named <code>todo_app</code></li>
          <li>Create Node.js API with Express and Mongoose</li>
          <li>Connect our frontend app to the Node.js API.</li>
        </ul>

        <p>Let's go!</p>

        <h3>Creating MongoDB database</h3>
        <p>In order to create a new database you need to run the following command:</p>
        <mdbsnippet>
          <code data-lang="shell" data-name="Shell">
            $ mdb database init -db mongodb
          </code>
        </mdbsnippet>
        <p>
          Now you need to provide your user data and then the database details. Please provide the
          values of your choice. For example:
        </p>
        <pre><code>? Enter username tony
? Enter password Stark_12
? Repeat password Stark_12
? Enter database name todo_app
? Enter description Database for the TODO app
</code></pre>
        <p class="note note-warning">
          <strong>Note:</strong> the password must contain <i>at least</i> one uppercase letter, one
          lowercase letter, one number, one special symbol and have minimum length of 8.
        </p>

        <p>Hit <kbd>Enter</kbd> and it's done.</p>

        <p>
          Please notice that in the command output the username and database name slightly differs
          from what you provided earlier. Don't worry - it's OK. A few random characters have been
          added to these values to randomize them and improve security of your database credentials.
        </p>
        <p class="note note-danger">
          <strong>Important:</strong> Do not close your terminal window until you save your
          credentials somewhere. This is the only time we will show you your database password. If
          you won't save it you'll loose it.
        </p>

        <p>
          That's pretty much it. You can now see how to connect with this database from the Node.js
          API.
        </p>

        <p class="note note-warning">
          <strong>Note:</strong> in MongoDB you don't need to create collections before they are
          used. MongoDB will create a collection when it's first time accessed.
        </p>

        <h3>Creating Node.js API with Express and Mongoose</h3>
        <p>
          In case you don't know, Mongoose is a MongoDB object modeling tool. It helps managing
          MongoDB access and models. You can initialize a MDB GO starter that already has configured
          Mongoose. Simply run the following command:
        </p>
        <mdbsnippet>
          <code data-lang="shell" data-name="Shell">
            $ mdb backend init
          </code>
        </mdbsnippet>
        <p>and choose <code>Express.js + MongoDB API starter</code> from the list that shows up.</p>
        <p>
          After initialization just go to the newly created project directory and open the
          <code>.env</code> file. After that edit the <code>DB_CONNECTION_STRING</code> value. You
          should paste the connection string that's been shown to you in the previous step. In my
          case the updated value looks like this:
        </p>
        <pre><code>DB_CONNECTION_STRING=mongodb://tonye9c88223:Stark_12@mongo.db.mdbgo.com:8604/todo_appbd2f70e0</code></pre>
        <p>Save the file and close it.</p>
        <p>
          The starter project is ready to use. You don't have to change anything to run the example
          app for the sake of this tutorial. Simply publish it using the following command:
        </p>
        <mdbsnippet>
          <code data-lang="shell" data-name="Shell">
            $ mdb publish -p node12
          </code>
        </mdbsnippet>

        <p>
          After your files get uploaded you can access your app under the address shown in the
          output.
        </p>

        <p class="note note-danger">
          <strong>Note:</strong> You may want to check
          <a href="https://mdbgo.com/docs/tutorials/node/">the tutorial</a> where we explain in
          detail what can go wrong here and how to deal with it.
        </p>

        <p class="note note-warning">
          <strong>Note:</strong> Since we need to install dependencies and run your app, it may take
          a few moments until it will be available under the provided URL.
        </p>

        <p>
          When you open the app URL you will see the default view on the <code>/</code> endpoint but
          when you'll visit <code>/tasks</code> you will see an empty array indicating that the
          <code>tasks</code> collection has been created and is empty. There are also other
          endpoints defined like this:
        </p>
        <ul>
          <li><code>GET /tasks/:id</code></li>
          <li><code>POST /tasks</code></li>
          <li><code>PUT /tasks/:id</code></li>
          <li><code>DELETE /tasks/:id</code></li>
        </ul>

        <p>
          These are self-explanatory but if you don't know how to operate on that go and check the
          <a href="https://mdbgo.com/docs/tutorials/node/">tutorial</a> where it is explained.
        </p>

        <p>
          Alright, only one step left for the fully-working TODO app - Angular frontend. Let's
          create it.
        </p>

        <h3>Connecting to the API via Angular app</h3>
        <p>
          We won't show how to create the whole Angular app here. Instead, you'll learn how to
          connect to the API <strong>assuming you already have a working app</strong>.
        </p>
        <p>Here's what we are going to do:</p>
        <ul>
          <li>Import <code>HttpClientModule</code> in the <code>app/app.module.ts</code> file</li>
          <li>Create an <code>TodoApiService</code> that will perform requests</li>
          <li>
            Demonstrate how to use our service in an example
            <code>app/todo-list.component.ts</code> component
          </li>
        </ul>

        <p>So the first thing is quite quick - let's see how to do it</p>

        <h4>Importing <code>HttpClientModule</code></h4>

        <p>
          You surely have the <code>app/app.module.ts</code> file in your app. Open it and do two
          things:
        </p>
        <ul>
          <li>
            Add the following import at the top of the file:
            <!-- prettier-ignore -->
            <mdbsnippet>
              <code data-lang="typescript" data-name="app.module.ts">
                import { HttpClientModule } from '@angular/common/http';
              </code>
            </mdbsnippet>
          </li>
          <li>
            Add <code>HttpClientModule</code> to the <code>imports</code> array like this:
            <!-- prettier-ignore -->
            <mdbsnippet>
              <code data-lang="typescript" data-name="app.module.ts">
                // ... imports: [ // ... other modules, HttpClientModule ] // ...
              </code>
            </mdbsnippet>
          </li>
        </ul>

        <p>Now let's create the <code>TodoApiService</code> service.</p>

        <h4>Creating <code>TodoApiService</code></h4>
        <p>
          In order to do that you can make use of the Angular CLI and generate appropriate class.
          Just run this command:
        </p>
        <!-- prettier-ignore -->
        <mdbsnippet>
          <code data-lang="shell" data-name="Shell">
            $ ng g s todo-api
          </code>
        </mdbsnippet>

        <p>
          It will generate necessary files and add required imports where necessary. Open the
          <code>app/todo-api.service.ts</code> file.
        </p>

        <p>
          Next step is to add required imports. In order to do that add the following lines at the
          top of the file:
        </p>
        <!-- prettier-ignore -->
        <mdbsnippet>
          <code data-lang="typescript" data-name="todo-api.service.ts">
            import { HttpClient } from '@angular/common/http'; import { Observable, throwError }
            from 'rxjs'; import { catchError, retry } from 'rxjs/operators';
          </code>
        </mdbsnippet>

        <p>Now, inject the module into the constructor like this:</p>
        <!-- prettier-ignore -->
        <mdbsnippet>
          <code data-lang="typescript" data-name="todo-api.service.ts">
            @Injectable({
              providedIn: 'root'
            })
            export class TodoApiService {
                constructor(private http: HttpClient) { }
            }
          </code>
        </mdbsnippet>

        <p>
          Alright, let's add CRUD operations so that we could talk to our API. Before we do that
          let's <code>apiUrl</code> field in our class so that we don't have to repeat it every
          time:
        </p>
        <!-- prettier-ignore -->
        <mdbsnippet>
          <code data-lang="typescript" data-name="todo-api.service.ts">
            @Injectable({
              providedIn: 'root'
            })
            export class TodoApiService {
              apiUrl = 'http://express-mongoose-starter.mdbgo.io'; // in your case it will be different

              constructor(private http: HttpClient) { }
            }
          </code>
        </mdbsnippet>

        <p>
          In order to read data from the server we need to make a <code>GET /tasks</code> request.
          You can do it like this:
        </p>
        <!-- prettier-ignore -->
        <mdbsnippet>
          <code data-lang="typescript" data-name="todo-api.service.ts">
            getTasks() {
              return this.http.get(`${this.apiUrl}/tasks`);
            }
          </code>
        </mdbsnippet>

        <p>
          It's a new method that performs the GET request and returns the result. We will take care
          of this result later. In a meantime let's add the remaining three methods:
        </p>
        <!-- prettier-ignore -->
        <mdbsnippet>
          <code data-lang="typescript" data-name="todo-api.service.ts">
            addTask(name: string, desc: string) {
              return this.http.post(`${this.apiUrl}/tasks`, { name, desc });
            }

            updateTask(id: number, name: string, desc: string) {
              return this.http.put(`${this.apiUrl}/tasks/${id}`, { name, desc });
            }

            deleteTask(id: number) {
              return this.http.delete(`{this.apiUrl}/tasks/${id}`);
            }
          </code>
        </mdbsnippet>

        <p>
          These are very simple methods that work the same way as the first one - performing POST,
          PUT and DELETE requests and returning the result.
        </p>

        <p>Alright, let's find out how to use this.</p>

        <h4>Using the <code>TodoApiService</code> in an example component</h4>

        <p>
          Assume you have a component named <code>TodoListComponent</code> where you want to display
          a list of tasks from the database. You need to make an API request to fetch the real data.
        </p>
        <p>
          This is how you can make use of our service. First, import your service and inject it into
          the constructor:
        </p>
        <!-- prettier-ignore -->
        <mdbsnippet>
          <code data-lang="typescript" data-name="todo-list.component.ts">
            import { Component, OnInit } from '@angular/core';
            import { TodoApiService } from '../todo-api.service.ts';

            @Component({
                selector: 'app-todo-list',
                templateUrl: './todo-list.component.html',
                styleUrls: ['./todo-list.component.scss']
            })
            export class TodoListComponent implements OnInit {

                constructor(private api: TodoApiService) { }

                ngOnInit() {
                }
            }
          </code>
        </mdbsnippet>

        <p>Now you can simply invoke our service method like this:</p>
        <!-- prettier-ignore -->
        <mdbsnippet>
          <code data-lang="typescript" data-name="todo-list.component.ts">
            ngOnInit() {
                this.api.getTasks()
                    .subscribe((tasks) => {
                      this.tasks = tasks;
                    });
            }
          </code>
        </mdbsnippet>

        <p>
          It will make an API request and assign the result to the <code>tasks</code> field in your
          component (we did not show how to create one).
        </p>

        <p>Making POST, PUT and DELETE requests is just as easy:</p>
        <!-- prettier-ignore -->
        <mdbsnippet>
          <code data-lang="typescript" data-name="todo-list.component.ts">
            createTask() {
                this.api.addTask('Wash the dishes', 'will take a while')
                    .subscribe((newTask) => {
                      this.tasks.push(newTask);
                    });
            }

            updateTask() {
                const currentTaskId = 1;
                this.api.updateTask(currentTaskId, 'Wash the dishes', 'Will take 30 mins')
                    .subscribe((updatedTask) => {
                        const oldTask = this.tasks.find((t => t.id === currentTaskId));
                        oldTask.id = updatedTask.id;
                        oldTask.name = updatedTask.name;
                        oldTask.desc = updatedTask.desc;
                    });
            }

            deleteTask() {
                const currentTaskId = 1;
                this.api.deleteTask(currentTaskId)
                    .subscribe(() => {
                        const idx = this.tasks.findIndex(t => t.id === currentTaskId);
                        this.tasks.splice(idx, 1);
                    });
            }
          </code>
        </mdbsnippet>

        <p>And that's how you communicate with your API from the Angular app.</p>
      </div>
    </div>
  </section>

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