This blog is a continuation of a three-part blog series on creating a real-time Trello board. This is going to be part 2 of the series. In the previous blog, we designed and implemented the API layer of the application. We added two tables i.e User and Task and also added the structs for the two tables. We've added and tested the API layer in the iex shell and it is working as per our expectations. In this blog, we are going to add the Trello board, Task cards, and integrate the functionalities with the previously designed API.

Blog series!!!

This is a 3 part blog series.

Part 1: We will be generating the application, adding the different tables, and the API layer, and we will test the API layer in the iex shell
Part 2: We will build the board, add tasks UI, and integrate the board with the functions (API) we created in Part 1 (This is Part 2)
Part 3: We will be adding real-time behavior to our board (under development)

Plan of attack

Getting the board and card UI ready ✓
Adding drag and drop feature to cards ✓
Adding JS hook and integrating with the UI✓
Integrating the UI with the API ✓

Getting the skeleton ready i.e Board

As per our planning, in this part of the series, we have to create our Trello board with cards and drag-drop functionality.
We are going to add our dashboard in our root URL of the application.

For this, we will open router.ex and add the following code

scope "/", TrelloAppWeb do
  pipe_through :browser

  live "/", HomeLive
end

We have registered the root URL i.e / with the home_live file.

Now, create a file trello_app/lib/trello_app_web/live/home_live.ex and add following code

defmodule TrelloAppWeb.HomeLive do
  use TrelloAppWeb, :live_view

  def mount(_params, _session, socket) do
    { :ok, socket }
  end
end

Before creating any view of the LiveView we will add some styling for the board and the cards.

Open the app.css file in the assets folder and paste the following CSS stylings.

html {
  font-family: sans-serif;
  background: #b1dade;
  color: #4a6064;
  font-weight: 400;
}

body {
  margin: 0;
}

* {
  box-sizing: border-box;
}

h1, h2, h3, h4, h5, h6 {
  font-weight: 400;
}

h1 {
  margin: 0;
  background: #303945;
  color: #fff;
  font-weight: 400;
  padding: 0.5rem;
  font-size: 1.2rem;
}

main {
  display: flex;
  flex-direction: column;
  height: 100vh;
  overflow: hidden;
}

.fullwidth {
  width: 100%;
}

.board {
  flex-grow: 1;
  width: 100%;
  padding: 1rem;
  overflow: scroll;
  display: flex;
  align-items: flex-start;
}

.list {
  margin: 0;
  min-width: 14rem;
  flex-basis: calc(100% / 6 - 1rem);
  padding: 0;
  list-style: none;
  margin: 0.5rem;
  background: #e7f3f4;
  color: #4a6064;
  border-radius: 0.2rem;
  overflow: hidden;
  padding-bottom: 8px;
}

.list-form {
  margin: 0;
  min-width: 14rem;
  flex-basis: calc(100% / 6 - 1rem);
  padding: 0;
  list-style: none;
  margin: 0.5rem;
  background: #e7f3f4;
  color: #4a6064;
  border-radius: 0.2rem;
  overflow: hidden;
}

.list-form form {
  padding: 0.5rem;
}

.list-form form > * + * {
  margin-top: 0.5rem;
}

.list-form h2,
.list-header {
  font-size: 0.8rem;
  font-weight: 600;
  margin: 0;
  padding: 0.5rem;
  padding-bottom: 0;
}

.list-footer {
  margin-top: 0.5rem;
  padding: 0.5rem;
  overflow: auto;
  background: #ddeff0;
  color: #4a6064;
}

.card {
  margin: 0.5rem;
  margin-bottom: 0;
  background: #fff;
  color: #4a6064;
  padding: 0.5rem;
  border-radius: 0.2rem;
  height: 100px;
}

.card:first-of-type {
  margin: 0;
}

.card a {
  color: inherit;
  text-decoration: none;
}

Now, add a file home_live.html.heex in the same folder(of home_live.ex) and add h1 tag with some random message for testing purposes.
As per our design we want three columns planning, progress, and completed to display our cards. Refer to the below image to get an idea.

Now, in the home_live.html.heex add these three columns with id as per the status.

<div class="board" id="trello-board">
  <ul class="list" id="planning">
      <div class="list-header"> Planning </div>
  </ul>

  <ul class="list" id="progress">
     <div class="list-header"> In Progress </div>
  </ul>

  <ul class="list" id="completed">
     <div class="list-header"> In Progress </div>
  </ul>
</div>

It will just create empty columns without any card because we haven't added any.

Getting the Card ready

If you remember we have created a function get_grouped_tasks/0 in the Project context.
We will assign the value of this function to the assigns in the mount function and later will iterate over these values in the view.

In the mount function of the home_live.ex, add the following code.

defmodule TrelloAppWeb.HomeLive do
  ....
  alias TrelloApp.Organization

  def mount(_params, _session, socket) do
    tasks = Organization.get_grouped_tasks()
    {:ok, assign(socket, tasks: tasks)}
  end  
end

We added an alias of the Organization context and assigned tasks to the socket using the get_grouped_tasks function.
If you remember get_grouped_tasks returns key-value pair of task status as key and a list of tasks as value.

Something like this

%{
"planning" => [
    %TrelloApp.Organization.Task{
      __meta__: #Ecto.Schema.Metadata<:loaded, "tasks">,
      description: "designing api",
      id: 2,
      inserted_at: ~N[2022-08-25 09:30:08],
      state: "planning",
      title: "Designing API",
      updated_at: ~N[2022-08-25 09:30:08],
      user: %TrelloApp.Organization.User{
        __meta__: #Ecto.Schema.Metadata<:loaded, "users">,
        first_name: "Michael",
        id: 1,
        inserted_at: ~N[2022-08-25 08:45:25],
        last_name: "holding",
        tasks: #Ecto.Association.NotLoaded<association :tasks is not loaded>,
        updated_at: ~N[2022-08-25 08:45:25]
      },
      user_id: 1
    }
],
"progress" => [
    // two tasks under progress
    %TrelloApp.Organization.Task{ id: 2 },  
    %TrelloApp.Organization.Task{ id: 3 }
 ],
 "completed" => [
    // one task under completed
    %TrelloApp.Organization.Task{id: 4}
 ]
}

Now, we will iterate over each of the lists in each column.

<div class="board" id="trello-board">
    <ul class="list" id="planning">
        <div class="list-header"> Planning </div>
        <%= for task <- @tasks["planning"] || [] do %>
           <li class="card">
              <a href><%= task.title %></a>
               <i><%= full_name({title.user}) %></i>
            </li>
        <% end %>
    </ul>

    <ul class="list" id="progress">
       <div class="list-header"> In Progress </div>
       <%= for task <- @tasks["progress"] || [] do %>
           <li class="card">
              <a href><%= task.title %></a>
               <i><%= full_name({title.user}) %></i>
            </li>
        <% end %>
    </ul>

    <ul class="list" id="completed">
       <div class="list-header"> In Progress </div>
       <%= for task <- @tasks["completed"] || [] do %>
           <li class="card">
              <a href><%= task.title %></a>
               <i><%= full_name({title.user}) %></i>
            </li>
        <% end %>
    </ul>
</div>

This will render all cards in each column. Now, we will work on adding the drag and drop feature to our board.

Adding drag and drop feature to cards

I wanted a vanilla javascript library that should be lightweight and highly supportive in the js community. While doing some research I came across sortable-js. Let's install it in the application. Navigate to the assets directory by running cd assets then run

  npm install sortablejs --save

I went through sortablejs documentation and came across a create method which can help us to move the cards from one point to another.
It takes the element reference of the column that you want to be sortable as the first argument and the second argument will be an object with different properties you want to apply(as per documentation).
```
  Sortable.create(planning, {
      group: 'shared',
      animation: 150,
      sort: false,
      onEnd: function (/**Event*/evt) {}
  });
```
The last property in the object i.e onEnd callback is where we have to do all manipulation. It is going to execute as soon as we drop the card on the other column. It has one event parameter which will have all information like the detail of the dragged element and the column where it is dropped.

Adding meta-data to each card

We've discussed the onEnd callback in the create method. It has some information about the dragged element and the point where it is dropped.

We are going to add a data property with the name task-id and value as id of the task on each card. Notice, the data-task-id property in the li tag.

  <%= for task <- @tasks["completed"] || [] do %>
     <li class="card" data-task-id={"#{task.id}"}> <==Notice this
        <a href><%= task.title %></a>
         <i><%= full_name({title.user}) %></i>
      </li>
    <% end %>

This data-task-id will act as the information of the element that is being dragged.
Also, if you remember the id on each column i.e ul tag, will act as information where the card is being dropped.
```
<ul class="list" id="completed">
```

So, in onEnd callback we can access id and taskId as follows

  console.log(`Id: ${evt.to.id}`) 
  console.log(`taskId: ${evt.item.dataset.taskId}`)

We will use this information when we are going to write our javascript hook to make all things work.

Adding Javascript Hook

We have installed sortablejs and discussed the method and made some changes in the Html to make it work with our javascript logic. Now, we will add the javascript logic. We will add a mounted callback, which is called and initialized with some initial value as soon as the element on which we are applying it is mounted in the DOM.

Let's add a file in trello_board.js in assets/js folder.

We will initialize Sortable.create for all of the three columns. We will get all of the three columns using document.getElementById('column_id'). Refer to the code below.

import Sortable from 'sortablejs';

TrelloBoard = {
  mounted(){ 
    const planning = document.getElementById('planning')
    const progress = document.getElementById('progress')
    const completed = document.getElementById('completed')
    const pushEvent = (target, taskId) => {
      this.pushEvent("move_task", {target, taskId})
    }

    Sortable.create(planning, {
        group: 'shared',
        animation: 150,
        sort: false,
        onEnd: function (/**Event*/evt) {
          pushEvent(evt.to.id, evt.item.dataset.taskId) 
        }
    });

    Sortable.create(progress, {
        group: 'shared',
        animation: 150,
        sort: false,
        onEnd: function (/**Event*/evt) {
          pushEvent(evt.to.id, evt.item.dataset.taskId) 
        }
    });

    Sortable.create(completed, {
        group: 'shared',
        animation: 150,
        sort: false,
        onEnd: function (/**Event*/evt) {
          pushEvent(evt.to.id, evt.item.dataset.taskId) 
        }
    });
}
export default TrelloBoard

Everything seems similar to what we discussed earlier, except the pushEvent function.
This function is initialized on the fourth line of the mounted function and it takes target and taskId as the parameter and creates an event "move_task"usingthis.pushEvent` function and passes these two parameters as an object.
At last but not least we will include our TrelloBoard hook in our LiveSocket. For this, we will open the app.js file and import TrelloBoard and include it in our Hooks object, and add the Hooks to our LiveSocket constructor as follows.
```
  import TrelloBoard from "./trello_board"
  let Hooks = { TrelloBoard }

  let liveSocket = new LiveSocket("/live", Socket, {params: {_csrf_token: csrfToken}, hooks: Hooks }) 
  # Notice `hooks: Hooks`
```

Calling the Hook

To call our Javascript logic i.e hook we’ll add the phx-hook attribute on the Trello board with value as the hook name i.e TrelloBoard where we want to perform our drag-drop operations.

<div class="board" id="trello-board" phx-hook="TrelloBoard">
  <ul class="list" id="planning">
    <div class="list-header"> Planning </div>
      .........
      .........
      .........
   // Remaining UI code
</div>

Handling `move_task` event in LiveView

In our javascript hooks onEnd callback we created a pushEvent named move_task which also sends target and taskId.
In LiveView, the events which are sent by the client using pushEvents can be handled using handle_event.

Open thehome_live.ex file and add the following function.

defmodule TrelloAppWeb.HomeLive do
   .........
   .........
   .........

  def handle_event("move_task", %{"target" => target, "taskId" => taskId}, socket) do
      Project.change_task_state(taskId, target)
      {:noreply, socket}
  end
end

As you can see in this handle_event function we are extracting target and taskId using pattern matching.
Later, we used the change_task_state/2 function(which we created in Part 1 of this blog series) and passed the taskId and target parameters to the function.
This not only moves the card in UI but also persists the state in the database.

This completes the second blog of this series. In this part, we build the board, add tasks UI along with drag and drop functionality and integrated the board with our API layer. In the next part, we will make our Trello board in real-time. I hope you like this blog. If you have any questions then please comment below. Thanks for reading 😊.

Creating a real-time Trello board with Phoenix LiveView-Part-2

Table of contents

Blog series!!!

Plan of attack

Getting the skeleton ready i.e Board

Getting the Card ready

Adding drag and drop feature to cards

Adding meta-data to each card

Adding Javascript Hook

Calling the Hook

Handling `move_task` event in LiveView

References

Subscribe to my newsletter

AbulAsar S.

AbulAsar S.

Creating a real-time Trello board with Phoenix LiveView-Part-2

Table of contents

Blog series!!!

Plan of attack

Getting the skeleton ready i.e Board

Getting the Card ready

Adding drag and drop feature to cards

Adding meta-data to each card

Adding Javascript Hook

Calling the Hook

Handling move_task event in LiveView

References

Subscribe to my newsletter

AbulAsar S.

AbulAsar S.

Handling `move_task` event in LiveView