[RUBY] Continued ・ Flow to implement image posting function using ActiveStorage

Introduction

Explanation from image saving to display using Active Storage. In my last post, I explained how to install Active Storage.

Link ↓ Flow to implement image posting function using ActiveStorage

Flow from saving an image to displaying it

1. Definition of association
2. Allow strong parameters to save images
3. Generated as HTML img element
4. Error resolution
5. Image resizing
6. Validation settings

1. Definition of association

Use the has_one_attached method to associate each record with the image file in a one-to-one relationship. Describe in the model file you want to link

model

class model< ApplicationRecord
 has_one_attached :file name
end

For the file name, set the name when calling. It also becomes a parameter key. ex):image, :file etc As an image, it feels like there is a file name column with attachments in it. By making this association, You can access the attached file with model name.file name.

2. Allow strong parameters to save images

controllers

 params.require(:message).permit(:text, :image)

As mentioned when defining the association, use the file name as the parameter key. Even at this time, the image that the column is formed will be applicable.

The above is the flow until storage.

The following is the flow until it is displayed.

3. Generated as HTML img element

Generate an img tag in HTML using a helper method called ʻimage_tag method`.

html.erb

<%= image_tag model name.file name%>
<%= image_tag message.image %>  #Example

Since it is associated, the image can be displayed by describing only model name.file name.

Basically, the image can be displayed up to this point. However, if there is no image at this rate, an error will occur.

4. Error resolution

Conditionally branch to the previous ʻimage_tag method` with an if statement.

html.erb

<%= image_tag message.image, if message.image.attached? %>

If an image is attached with the ʻattached? method`, it returns true and is read. If no image is attached, it returns false, is not loaded and no error occurs.

5. Image resizing

Use the variant method, which is a method that can be used when ActiveStorage is installed. If you add it to the above code,

html.erb

<%= image_tag message.image.variant(resize: '500×500'), if message.image.attached? %>

If you specify the display size of the image, it will not be larger than that.

6. Validation settings

In the current situation, if you imagine LINE, you will get an error if you do not have both text and image. Since it is not easy to use, the specification is that either text or image should exist.

model

validates :message, presence: true, unless: :was_attacher?

def was_attached?
 self.image.attached?
end

If the return value of the method is false, validation is verified. (If message does not exist)

Finally

It's too convenient to be able to easily access images just by associating! !!