使用PETAL(Phoenix、Elixir、TailwindCSS、AlpineJS、LiveView)技术栈构建一个简化版的Instagram Web应用程序
在第 3 部分中，我们添加了个人资料页面以及关注和显示帐户的功能，在这部分中，我们将处理用户的帖子。您可以赶上Instagram 克隆 GitHub Repo。
让我们首先添加一个路由来显示用于添加帖子的表单，打开lib/instagram_clone_web/router.ex：
scope "/", InstagramCloneWeb do
pipe_through :browser
live "/", PageLive, :index
live "/:username", UserLive.Profile, :index
live "/p/:id", PostLive.Show # <-- THIS LINE WAS ADDED
end
scope "/", InstagramCloneWeb do
pipe_through [:browser, :require_authenticated_user]
get "/users/settings/confirm_email/:token", UserSettingsController, :confirm_email
live "/accounts/edit", UserLive.Settings
live "/accounts/password/change", UserLive.PassSettings
live "/:username/following", UserLive.Profile, :following
live "/:username/followers", UserLive.Profile, :followers
live "/p/new", PostLive.New # <-- THIS LINE WAS ADDED
end在文件夹中创建我们的实时视图文件lib/instagram_clone_web/live/post_live：
lib/instagram_clone_web/live/post_live/new.ex lib/instagram_clone_web/live/post_live/new.html.leex lib/instagram_clone_web/live/post_live/show.ex lib/instagram_clone_web/live/post_live/show.html.leex
里面lib/instagram_clone_web/live/post_live/new.ex：
defmodule InstagramCloneWeb.PostLive.New do
use InstagramCloneWeb, :live_view
@impl true
def mount(_params, session, socket) do
socket = assign_defaults(session, socket)
{:ok,
socket
|> assign(page_title: "New Post")}
end
end打开lib/instagram_clone_web/live/header_nav_component.html.leex在第18行，使用我们的新route：
<%= live_redirect to: Routes.live_path(@socket, InstagramCloneWeb.PostLive.New) do %>
让我们创建一个帖子上下文，转到终端：
$ mix phx.gen.context Posts Post posts url_id:string description:text photo_url:string user_id:references:users total_likes:integer total_comments:integer
打开生成的迁移并添加以下内容：
defmodule InstagramClone.Repo.Migrations.CreatePosts do
use Ecto.Migration
def change do
create table(:posts) do
add :url_id, :string
add :description, :text
add :photo_url, :string
add :total_likes, :integer, default: 0
add :total_comments, :integer, default: 0
add :user_id, references(:users, on_delete: :nothing)
timestamps()
end
create index(:posts, [:user_id])
create unique_index(:posts, [:url_id])
end
end返回终端：$ mix ecto.migrate
我们还可以在终端中将帖子计数添加到用户架构中：
$ mix ecto.gen.migration adds_posts_count_to_users
打开生成的迁移并添加以下内容：
defmodule InstagramClone.Repo.Migrations.AddsPostsCountToUsers do
use Ecto.Migration
def change do
alter table(:users) do
add :posts_count, :integer, default: 0
end
end
end返回终端：$ mix ecto.migrate
打开lib/instagram_clone/accounts/user.ex并将架构编辑为以下内容：
@derive {Inspect, except: [:password]}
schema "users" do
field :email, :string
field :password, :string, virtual: true
field :hashed_password, :string
field :confirmed_at, :naive_datetime
field :username, :string
field :full_name, :strin
field :avatar_url, :string, default: "/images/default-avatar.png"
field :bio, :string
field :website, :string
field :followers_count, :integer, default: 0
field :following_count, :integer, default: 0
field :posts_count, :integer, default: 0 # <-- THIS LINE WAS ADDED
has_many :following, Follows, foreign_key: :follower_id
has_many :followers, Follows, foreign_key: :followed_id
has_many :posts, InstagramClone.Posts.Post # <-- THIS LINE WAS ADDED
timestamps()
end
打开lib/instagram_clone/posts/post.ex添加以下内容：
defmodule InstagramClone.Posts.Post do
use Ecto.Schema
import Ecto.Changeset
schema "posts" do
field :description, :string
field :photo_url, :string
field :url_id, :string
field :total_likes, :integer, default: 0
field :total_comments, :integer, default: 0
belongs_to :user, InstagramClone.Accounts.User
timestamps()
end
@doc false
def changeset(post, attrs) do
post
|> cast(attrs, [:url_id, :description, :photo_url])
|> validate_required([:url_id, :photo_url])
end
end让我们添加新的架构，并允许在其中上传lib/instagram_clone_web/live/post_live/new.ex：
defmodule InstagramCloneWeb.PostLive.New do
use InstagramCloneWeb, :live_view
alias InstagramClone.Posts.Post
alias InstagramClone.Posts
@extension_whitelist ~w(.jpg .jpeg .png)
@impl true
def mount(_params, session, socket) do
socket = assign_defaults(session, socket)
{:ok,
socket
|> assign(page_title: "New Post")
|> assign(changeset: Posts.change_post(%Post{}))
|> allow_upload(:photo_url,
accept: @extension_whitelist,
max_file_size: 30_000_000)}
end
@impl true
def handle_event("validate", %{"post" => post_params}, socket) do
changeset =
Posts.change_post(%Post{}, post_params)
|> Map.put(:action, :validate)
{:noreply, socket |> assign(changeset: changeset)}
end
def handle_event("cancel-entry", %{"ref" => ref}, socket) do
{:noreply, cancel_upload(socket, :photo_url, ref)}
end
end打开config/dev.exs第 61 行编辑：
~r"priv/static/[^uploads].*(js|css|png|jpeg|jpg|gif|svg)$",该配置可以避免每次上传文件时重新加载上传文件夹的实时重新加载，否则，您在尝试上传时会遇到奇怪的行为。
在里面添加以下内容lib/instagram_clone_web/live/post_live/new.html.leex：
<%= @page_title %>
<%= f = form_for @changeset, "#",
class: "mt-8",
phx_change: "validate",
phx_submit: "save" %>
<%= for {_ref, err} <- @uploads.photo_url.errors do %>
<%= Phoenix.Naming.humanize(err) %>
<% end %>
<%= live_file_input @uploads.photo_url, class: "cursor-pointer relative block opacity-0 w-full h-full p-20 z-30" %>
Drop files anywhere to upload
or
Select Files
<%= for entry <- @uploads.photo_url.entries do %>
<% end %>
<%= label f, :description, class: "font-semibold" %>
<%= textarea f, :description, class: "w-full border-2 border-gray-400 rounded p-1 text-semibold text-gray-500 focus:ring-transparent focus:border-gray-600", rows: 5 %>
<%= error_tag f, :description, class: "text-red-700 text-sm block" %>
<%= submit "Submit",
phx_disable_with: "Saving...",
class: "py-2 px-6 border-none shadow rounded font-semibold text-sm text-gray-50 hover:bg-light-blue-600 bg-light-blue-500 cursor-pointer" %>
lib/instagram_clone_web/live/uploaders在创建一个名为的文件下，post.ex在该文件中添加以下内容：
defmodule InstagramClone.Uploaders.Post do
alias InstagramCloneWeb.Router.Helpers, as: Routes
alias InstagramClone.Posts.Post
@upload_directory_name "uploads"
@upload_directory_path "priv/static/uploads"
defp ext(entry) do
[ext | _] = MIME.extensions(entry.client_type)
ext
end
def put_image_url(socket, %Post{} = post) do
{completed, []} = Phoenix.LiveView.uploaded_entries(socket, :photo_url)
urls =
for entry <- completed do
Routes.static_path(socket, "/#{@upload_directory_name}/#{entry.uuid}.#{ext(entry)}")
end
%Post{post | photo_url: List.to_string(urls)}
end
def save(socket) do
if !File.exists?(@upload_directory_path), do: File.mkdir!(@upload_directory_path)
Phoenix.LiveView.consume_uploaded_entries(socket, :photo_url, fn meta, entry ->
dest = Path.join(@upload_directory_path, "#{entry.uuid}.#{ext(entry)}")
File.cp!(meta.path, dest)
end)
:ok
end
end打开lib/instagram_clone/posts.ex编辑create_post()并添加一个私有函数来放置 url id：
...
def create_post(%Post{} = post, attrs \\ %{}, user) do
post = Ecto.build_assoc(user, :posts, put_url_id(post))
changeset = Post.changeset(post, attrs)
update_posts_count = from(u in User, where: u.id == ^user.id)
Ecto.Multi.new()
|> Ecto.Multi.update_all(:update_posts_count, update_posts_count, inc: [posts_count: 1])
|> Ecto.Multi.insert(:post, changeset)
|> Repo.transaction()
end
# Generates a base64-encoding 8 bytes
defp put_url_id(post) do
url_id = Base.encode64(:crypto.strong_rand_bytes(8), padding: false)
%Post{post | url_id: url_id}
end
...添加lib/instagram_clone_web/live/post_live/new.ex以下事件处理函数：
alias InstagramClone.Uploaders.Post, as: PostUploader
def handle_event("save", %{"post" => post_params}, socket) do
post = PostUploader.put_image_url(socket, %Post{})
case Posts.create_post(post, post_params, socket.assigns.current_user) do
{:ok, post} ->
PostUploader.save(socket, post)
{:noreply,
socket
|> put_flash(:info, "Post created successfully")
|> push_redirect(to: Routes.user_profile_path(socket, :index, socket.assigns.current_user.username))}
{:error, %Ecto.Changeset{} = changeset} ->
{:noreply, assign(socket, changeset: changeset)}
end
end在第 52 行打开，lib/instagram_clone_web/live/user_live/profile.html.leex让我们显示我们的帖子数：
<%= @user.posts_count %> Posts 现在让我们创建一个函数来获取个人资料帖子并使用无限滚动对结果进行分页，打开lib/instagram_clone/posts.ex：
...
@doc """
Returns the list of paginated posts of a given user id.
## Examples
iex> list_user_posts(page: 1, per_page: 10, user_id: 1)
[%{photo_url: "", url_id: ""}, ...]
"""
def list_profile_posts(page: page, per_page: per_page, user_id: user_id) do
Post
|> select([p], map(p, [:url_id, :photo_url]))
|> where(user_id: ^user_id)
|> limit(^per_page)
|> offset(^((page - 1) * per_page))
|> order_by(desc: :id)
|> Repo.all
end
...打开lib/instagram_clone_web/live/user_live/profile.ex并分配帖子：
...
alias InstagramClone.Posts
@impl true
def mount(%{"username" => username}, session, socket) do
socket = assign_defaults(session, socket)
user = Accounts.profile(username)
{:ok,
socket
|> assign(page: 1, per_page: 15)
|> assign(user: user)
|> assign(page_title: "#{user.full_name} (@#{user.username})")
|> assign_posts(),
temporary_assigns: [posts: []]}
end
defp assign_posts(socket) do
socket
|> assign(posts:
Posts.list_profile_posts(
page: socket.assigns.page,
per_page: socket.assigns.per_page,
user_id: socket.assigns.user.id
)
)
end
@impl true
def handle_event("load-more-profile-posts", _, socket) do
{:noreply, socket |> load_posts}
end
defp load_posts(socket) do
total_posts = socket.assigns.user.posts_count
page = socket.assigns.page
per_page = socket.assigns.per_page
total_pages = ceil(total_posts / per_page)
if page == total_pages do
socket
else
socket
|> update(:page, &(&1 + 1))
|> assign_posts()
end
end
...一切都保持不变，我们只需分配页面并设置每页的限制，然后在我们的mount()函数中分配个人资料帖子。我们添加了一个事件处理函数，该函数将在模板中使用 javascript 挂钩触发，如果不是最后一页，它将加载更多页面。
lib/instagram_clone_web/live/user_live/profile.html.leex在文件底部打开以下内容：
...
<%= for post <- @posts do %>
<%= live_redirect img_tag(post.photo_url, class: "object-cover h-80 w-full"),
id: post.url_id,
to: Routes.live_path(@socket, InstagramCloneWeb.PostLive.Show, post.url_id) %>
<% end %>
我们将每个新页面附加到 posts div 中，底部有一个空的 div，每次可见时都会触发事件来加载更多页面。
打开assets/js/app.js并添加我们的钩子：
...
let Hooks = {}
Hooks.ProfilePostsScroll = {
mounted() {
this.observer = new IntersectionObserver(entries => {
const entry = entries[0];
if (entry.isIntersecting) {
this.pushEvent("load-more-profile-posts");
}
});
this.observer.observe(this.el);
},
destroyed() {
this.observer.disconnect();
},
}
let csrfToken = document.querySelector("meta[name='csrf-token']").getAttribute("content")
let liveSocket = new LiveSocket("/live", Socket, {
hooks: Hooks,
params: { _csrf_token: csrfToken },
dom: {
onBeforeElUpdated(from, to) {
if (from.__x) { Alpine.clone(from.__x, to) }
}
}
})
...每次到达或可见空页脚 div 时，我们使用观察者来推送事件以加载更多帖子。
打开lib/instagram_clone/posts.ex并添加一个函数来通过 url id 获取帖子：
...
def get_post_by_url!(id) do
Repo.get_by!(Post, url_id: id)
|> Repo.preload(:user)
end
...让我们在 mount 函数中分配 post lib/instagram_clone_web/live/post_live/show.ex：
defmodule InstagramCloneWeb.PostLive.Show do
use InstagramCloneWeb, :live_view
alias InstagramClone.Posts
alias InstagramClone.Uploaders.Avatar
@impl true
def mount(%{"id" => id}, session, socket) do
socket = assign_defaults(session, socket)
post = Posts.get_post_by_url!(URI.decode(id))
{:ok, socket |> assign(post: post)}
end
end我们正在对 URL ID 进行解码，因为在我们的个人资料模板中，当我们发布帖子时，live_redirect URL ID 会被编码。我们Base.encode64用来生成 id 的 ，有时会产生特殊字符，例如/需要在 URL 中进行编码的字符。
这就是这部分的内容，这是一项正在进行的工作。在下一部分中，我们将使用 show-post 页面。