Introduction

The implementation of the status feed that appears in the Rails tutorial was a bit complicated, so I'll summarize it myself.

Status feed

The status feed is a TL (tweet list) on Twitter. It is possible to display the posts of the users you are following.

Implementation method

Create a feed method.

`user.rb`


#Returns a feed of status.
def feed
end

First, I will draw from the conclusion. Describe as follows in the feed method.

`user.rb`


#Returns a feed of status.
  def feed
    following_ids = "SELECT followed_id FROM relationships WHERE follower_id = :user_id"
    Micropost.where("user_id IN (#{following_ids}) OR user_id = :user_id", user_id: id)
  end

Even if you look at this alone, it's Wakewakarimasen. Let's take a closer look. First, focus on the following.

`user.rb`


    following_ids = "SELECT followed_id FROM relationships WHERE follower_id = :user_id"

The above code is represented by a SQL statement and the SELECT command is used.

SQL command	meaning
SELECT	Search the data in the table.

SELECT command parameters	meaning
FROM	Specify the target source table.
WHERE	Set the condition of the value you want to get

In other words, what we mean here is ... This means that the followed_id column of the relationships table gets the users that match the user_id. You can get the following_ids variable ** following user information **.

Next, let's focus on the code below.

`user.rb`


Micropost.where("user_id IN (#{following_ids}) OR user_id = :user_id", user_id: id)

It uses the rails where method. The where method was also a little complicated to use, so I will organize it.

First, let's look at IN and OR. IN is used to define ** multiple conditions **. An example is given below.

#Single designation
#Gets the user whose age column is "20".
user = User.where("age = 20")

#Multiple designation
#Get users whose age column is "20 and 30".
user = User.where("age IN (20, 30)")

If you go back to the code above and think about it ... The value of user_id will get the post with the id value of following_ids (list of following users) defined earlier.

`user.rb`


Micropost.where("user_id IN (#{following_ids}) OR user_id = :user_id", user_id: id)

Next, let's focus on OR. OR means ** to get data that matches either condition **. An example is given below.

#Gets the user whose name column is "Taro" and whose age column is "20".
user = User.where("name = 'Taro' and age = 20")

If you go back to the code above and think about it ... If the value of user_id is the id of following_ids (list of following users) or "id" (your id), that value will be returned.

`user.rb`


Micropost.where("user_id IN (#{following_ids}) OR user_id = :user_id", user_id: id)

By the way, for the part of user_id =: user_id", user_id: id, the value specified by : is assigned to the value specified after ,.

`python`


#Gets the user whose age column is "20".
user = User.where("age = :xxx", xxx: 20)

#Gets the user whose age column is "20".
user = User.where("age = 20")

I understand the feed method. You can use the feed method as follows to get posts from users that the logged-in user is following.