爲什麼當我的表單中的實例變量返回nil時，該語句的賦值部分不是？

我app/views/videos/upload.html.erb看起來是這樣的：

<div class="bootstrap-styles"> 
<div class="modal-header"> 
    <button type="button" class="close" data-dismiss="modal" aria-hidden="true">×</button> 
    <h3 id="myModalLabel">Upload your Video</h3> 
    <p><i>Step 2 of 2 - TEST</i></p> 
    </div> 
    <div class="modal-body"> 
    <div class="form"> 
     <% binding.pry %> 
     <%= form_tag @upload_info[:url], :multipart => true do %> 
     <div>Step 2 of 2</div> 
     <%= hidden_field_tag :token, @upload_info[:token] %> 
     <%= file_field_tag :file, title: 'Choose video to upload' %> 
     <p class="uploader"> 
      <button class="btn btn-success ladda-button" data-color="green" data-style="expand-left"><span class="ladda-label">Upload Video</span><span class="ladda-spinner"></span></button> 
     </p> 
     <% end %> 

    </div> 
    </div> 
    <div class="modal-footer"> 
    </div> 
</div>

相應Videos#Upload控制器看起來是這樣的：

def upload 
    authorize! :read, @family_tree 
    @video = Video.find(params[:video_id]) 
    @upload_info = Video.token_form(@video, video_save_video_path(@family_tree, @video)) 

    respond_to do |format| 
     format.html 
     format.js 
    end 
    end

每當執行此upload動作，我得到這個錯誤：

NoMethodError - undefined method `[]' for nil:NilClass: 
    app/views/videos/upload.html.erb:9:in `_app_views_videos_upload_html_erb___1805626926918975871_70299844626480'

所以我爆發了我可信的binding.pry，這是它得到VELLY有趣/不可思議：

[1] pry(#<#<Class:0x007fdfea1e34e0>>)> @upload_info 
=> nil 
[2] pry(#<#<Class:0x007fdfea1e34e0>>)> @video 
=> #<Video id: 39, title: "Drones", description: "Down in drones", yt_video_id: nil, is_complete: nil, created_at: "2014-11-21 00:41:03", updated_at: "2014-11-21 00:41:03", reply_id: nil, circa: nil> 
[3] pry(#<#<Class:0x007fdfea1e34e0>>)> @family_tree 
=> #<FamilyTree id: 1, name: "'s Family Tree", user_id: 1, created_at: "2014-10-04 15:37:18", updated_at: "2014-10-04 15:37:18"> 
[4] pry(#<#<Class:0x007fdfea1e34e0>>)> Video.token_form(@video, video_save_video_path(@family_tree, @video)) 
=> {:url=> 
    "http://uploads.gdata.youtube.com/action/FormDataUpload/AIwbFASzqNJ1rg?nexturl=/videos/1/save_video.39", 
:token=> 
    "AI-SOME-TOKEN-b9ftw"} 
[5] pry(#<#<Class:0x007fdfea1e34e0>>)> video_save_video_path 
ActionController::UrlGenerationError: No route matches {:action=>"save_video", :controller=>"videos", :family_tree_id=>"1"} missing required keys: [:video_id] 
from /.rvm/gems/[email protected]/gems/actionpack-4.1.6/lib/action_dispatch/journey/formatter.rb:39:in `generate' 
[6] pry(#<#<Class:0x007fdfea1e34e0>>)> @upload_info 
=> nil 
[7] pry(#<#<Class:0x007fdfea1e34e0>>)> @upload_info[:url] 
NoMethodError: undefined method `[]' for nil:NilClass 
from (pry):8:in `_app_views_videos_upload_html_erb___1805626926918975871_70299841189460'

所以@upload_info如設置在我的控制器返回nil，但分配部分，即：

Video.token_form(@video, video_save_video_path(@family_tree, @video))

返回值我期待內撬。

編輯1

的Upload行動正在從叫我Video#Create控制器內，像這樣：

def create 
    authorize! :read, @family_tree 
    @video = Video.new(video_params) 

    respond_to do |format| 
     if @video.save 
     format.html { render action: 'upload' } 
     else 
     format.html { render action: 'new' } 
     format.json { render json: @video.errors, status: :unprocessable_entity } 
     end 
    end 
    end

我修改了upload行動，包括調試信息，和我看到什麼幸福寫入日誌文件 - 這表明Video#Upload動作未被執行。

這是有道理的，因爲我的Video#Create過程的日誌是這樣的：

Started POST "/family_trees/1/videos" for 127.0.0.1 at 2014-11-21 00:01:11 -0500 
Processing by VideosController#create as JS 
    Parameters: {"utf8"=>"✓", "video"=>{"title"=>"Hello There", "description"=>"Hello World", "circa"=>"", "user_ids"=>[""]}, "commit"=>"Add Video", "family_tree_id"=>"1"} 
    User Load (1.9ms) SELECT "users".* FROM "users" WHERE "users"."id" = 1 ORDER BY "users"."id" ASC LIMIT 1 
    FamilyTree Load (0.9ms) SELECT "family_trees".* FROM "family_trees" WHERE "family_trees"."user_id" = $1 LIMIT 1 [["user_id", 1]] 
    FamilyTree Load (2.8ms) SELECT "family_trees".* FROM "family_trees" WHERE "family_trees"."id" = $1 LIMIT 1 [["id", 1]] 
    (1.0ms) SELECT COUNT(*) FROM "roles" INNER JOIN "users_roles" ON "roles"."id" = "users_roles"."role_id" WHERE "users_roles"."user_id" = $1 AND (((roles.name = 'admin') AND (roles.resource_type IS NULL) AND (roles.resource_id IS NULL))) [["user_id", 1]] 
    Membership Load (1.6ms) SELECT "memberships".* FROM "memberships" WHERE "memberships"."user_id" = 1 AND "memberships"."family_tree_id" = 1 
    (2.2ms) BEGIN 
    SQL (3.0ms) INSERT INTO "videos" ("created_at", "description", "title", "updated_at") VALUES ($1, $2, $3, $4) RETURNING "id" [["created_at", "2014-11-21 05:01:11.486342"], ["description", "Hello World"], ["title", "Hello There"], ["updated_at", "2014-11-21 05:01:11.486342"]] 
    (2.4ms) COMMIT 
    Rendered videos/upload.html.erb within layouts/application (3.3ms) 
Completed 500 Internal Server Error in 42ms 

NoMethodError - undefined method `[]' for nil:NilClass: 
    app/views/videos/upload.html.erb:10:in `_app_views_videos_upload_html_erb___1805626926918975871_70299789284400'

所以它看起來像它試圖渲染videos/upload視圖而不執行控制器的作用。

如何讓它執行操作，但只有在@video.save已經工作？

來源

2014-11-21 marcamillion

它顯得有些怪異。你可以嘗試在form_tag參數周圍使用括號嗎？ '<％= form_tag（@upload_info [：url]，：multipart => true）do％>'？ – Anand 2014-11-21 04:24:46

另外，請在分配後立即在控制器中記錄'@ upload_info'，'@ video'和'@ family_tree'的值。 – Anand 2014-11-21 04:26:47

@Anand我用你的建議更新了這個問題 - 特別是記錄這些值的請求。 – marcamillion 2014-11-21 05:06:15

啊，這就是問題所在！ render action: 'upload'不會調用upload控制器方法。它只會呈現上傳視圖。因此@upload_info沒有被更新。使用redirect_to，而不是渲染得控制器代碼首先執行：

具體來說，替換：format.html { render action: 'upload' }與redirect_to upload_video_path(@video, ...)

來源

2014-11-21 05:16:08 Anand

這有效。完善。謝謝！ – marcamillion 2014-11-21 05:52:58

爲什麼當我的表單中的實例變量返回nil時，該語句的賦值部分不是？

回答

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