Rails-Gem-carrierwave 上传文件

# 步骤

## 安装
```
gem 'carrierwave'
```

cli中
```
bundle install
```

然后可以新建一个uploader
```
rails g uploader attachment
```

然后需要设置一下app/uploaders/attachment_uploader.rb，一般默认即可
```
  storage :file

def store_dir
    "uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
  end
```
结果大致是这样的
```
  # Include RMagick or MiniMagick support:
  # include CarrierWave::RMagick
  # include CarrierWave::MiniMagick

# Choose what kind of storage to use for this uploader:
  storage :file
  # storage :fog

# Override the directory where uploaded files will be stored.
  # This is a sensible default for uploaders that are meant to be mounted:
  def store_dir
    "uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
  end

```

## 使用
Model中
需要将其设置如下 ，当然需要先添加一个对应的column
```
rails g migration add_attachment_to_product
```

修改db/migrate/add_attachment_to_product.rb
```
class AddImgToProduct < ActiveRecord::Migration[5.0]
  def change
    add_column :products, :attachment, :string
  end
end
```

修改model挂载
```
class Resume < ApplicationRecord
    # 添加上传设置
    mount_uploader :attachment, AttachmentUploader
end
```

Controller中
注意打开上传的新项目
```
def product_params
    params.require(:product).permit(:title, :description, :image,:quantity, :price, :feet,:attachment)
end
```

View中
使用
```
<%= f.input :attachment ,label: '附件'%>
```
链接
```
      <% if resume.attachment.present? %>
      <a href="<%= resume.attachment_url %>" target="_blank" class="btn btn-primary btn-xs">预览</a>
      <% else %>
      <p>无附件</p>
      <% end %>
```
或者也可以用`image_tag`
```
<%= image_tag(current_user.avatar_url, :height => '120', :width => '90')  %>
```
文件名
```
.attachment_identifier
```

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