users: drop id_to_name, name_to_id caching.

Changes:

* Drop Users.id_to_name.
* Don't cache Users.name_to_id.
* Replace calls to name_to_id with find_by_name when possible.
* Don't autodefine creator_name in belongs_to_creator.
* Don't autodefine updater_name in belongs_to_updater.
* Instead manually define creator_name / updater_name only on models that need
  to return these fields in the api.

id_to_name was cached to reduce the impact of N+1 query patterns in
certain places, especially in api responses that return creator_name /
updater_name fields. But it still meant we were doing N calls to
memcache. Using `includes` to prefetch users avoids this N+1 pattern.

name_to_id had no need be cached, it was never used in any performance-
sensitive contexts.

Avoiding caching also avoids the need to keep these caches consistent.

app/views/artist_versions/_standard_listing.html.erb

@@ -37,7 +37,7 @@
           </td>
           <td>
             <%= link_to_user artist_version.updater %>
-            <%= link_to "»", artist_versions_path(search: { updater_name: artist_version.updater_name }) %>
+            <%= link_to "»", artist_versions_path(search: { updater_name: artist_version.updater.name }) %>
             <p>
               <%= compact_time(artist_version.updated_at) %>
               <% if CurrentUser.is_moderator? %>

app/views/comments/index.atom.builder

@@ -9,7 +9,7 @@ atom_feed(root_url: comments_url(host: Danbooru.config.hostname)) do |feed|
 
   @comments.each do |comment|
     feed.entry(comment, published: comment.created_at, updated: comment.updated_at) do |entry|
-      entry.title("@#{comment.creator_name} on post ##{comment.post_id} (#{comment.post.presenter.humanized_essential_tag_string})")
+      entry.title("@#{comment.creator.name} on post ##{comment.post_id} (#{comment.post.presenter.humanized_essential_tag_string})")
       entry.content(<<-EOS.strip_heredoc, type: "html")
         <img src="#{comment.post.preview_file_url}"/>
 
@@ -17,7 +17,7 @@ atom_feed(root_url: comments_url(host: Danbooru.config.hostname)) do |feed|
       EOS
 
       entry.author do |author|
-        author.name(comment.creator_name)
+        author.name(comment.creator.name)
         author.uri(user_url(comment.creator))
       end
     end

app/views/comments/partials/show/_comment.html.erb

@@ -1,6 +1,6 @@
 <% if CurrentUser.is_moderator? || (params[:search] && params[:search][:is_deleted] =~ /t/) || !comment.is_deleted? %>
   <a name="comment-<%= comment.id %>"></a>
-  <article class="comment <%= "below-threshold" if comment.below_threshold? %>" data-post-id="<%= comment.post_id %>" data-comment-id="<%= comment.id %>" data-score="<%= comment.score %>" data-creator="<%= comment.creator_name %>" data-is-sticky="<%= comment.is_sticky %>">
+  <article class="comment <%= "below-threshold" if comment.below_threshold? %>" data-post-id="<%= comment.post_id %>" data-comment-id="<%= comment.id %>" data-score="<%= comment.score %>" data-creator="<%= comment.creator.name %>" data-is-sticky="<%= comment.is_sticky %>">
     <div class="author">
       <h1>
         <%= link_to_user comment.creator %>

app/views/posts/index.atom.erb

@@ -29,7 +29,7 @@
         </div>
       </content>
       <author>
-        <name><%= post.uploader_name %></name>
+        <name><%= post.uploader.name %></name>
       </author>
     </entry>
   <% end %>

app/views/posts/partials/show/_image.html.erb

@@ -1,3 +1,3 @@
 <% if post.visible? %>
-  <%= image_tag(post.file_url_for(CurrentUser.user), :width => post.image_width_for(CurrentUser.user), :height => post.image_height_for(CurrentUser.user), :id => "image", "data-original-width" => post.image_width, "data-original-height" => post.image_height, "data-large-width" => post.large_image_width, "data-large-height" => post.large_image_height, "data-tags" => post.tag_string, :alt => post.presenter.humanized_essential_tag_string, "data-uploader" => post.uploader_name, "data-rating" => post.rating, "data-flags" => post.status_flags, "data-parent-id" => post.parent_id, "data-has-children" => post.has_children?, "data-has-active-children" => post.has_active_children?, "data-score" => post.score, "data-fav-count" => post.fav_count, "itemprop" => "contentUrl") %>
+  <%= image_tag(post.file_url_for(CurrentUser.user), :width => post.image_width_for(CurrentUser.user), :height => post.image_height_for(CurrentUser.user), :id => "image", "data-original-width" => post.image_width, "data-original-height" => post.image_height, "data-large-width" => post.large_image_width, "data-large-height" => post.large_image_height, "data-tags" => post.tag_string, :alt => post.presenter.humanized_essential_tag_string, "data-uploader" => post.uploader.name, "data-rating" => post.rating, "data-flags" => post.status_flags, "data-parent-id" => post.parent_id, "data-has-children" => post.has_children?, "data-has-active-children" => post.has_active_children?, "data-score" => post.score, "data-fav-count" => post.fav_count, "itemprop" => "contentUrl") %>
 <% end %>

app/views/posts/partials/show/_ugoira_original.html.erb

@@ -9,7 +9,7 @@
   "data-large-width" => post.image_width,
   "data-large-height" => post.image_height,
   "data-tags" => post.tag_string,
-  "data-uploader" => post.uploader_name,
+  "data-uploader" => post.uploader.name,
   "data-rating" => post.rating,
   "data-flags" => post.status_flags,
   "data-parent-id" => post.parent_id,

app/views/posts/show.html.erb

@@ -120,7 +120,7 @@
         <% if !CurrentUser.user.is_builder? %>
           <h2>Before commenting, read the <%= link_to "how to comment guide", wiki_pages_path(:search => {:title => "howto:comment"}) %>.</h2>
         <% end %>
-        <%= render "comments/partials/index/list", :comments => @post.comments.visible(CurrentUser.user), :post => @post, :show_header => false %>
+        <%= render "comments/partials/index/list", :comments => @post.comments.visible(CurrentUser.user).includes(:creator), :post => @post, :show_header => false %>
       </section>
 
       <section id="notes" style="display: none;">

app/views/reports/upload_tags.html.erb

@@ -15,7 +15,7 @@
       <tbody>
         <% @upload_reports.each do |upload_report| %>
           <tr>
-            <td><%= PostPresenter.preview(upload_report.becomes(Post), show_deleted: true, tags: "user:#{upload_report.uploader_name}") %></td>
+            <td><%= PostPresenter.preview(upload_report.becomes(Post), show_deleted: true, tags: "user:#{upload_report.uploader.name}") %></td>
             <td>
               <%= TagSetPresenter.new(upload_report.uploader_tags_array).inline_tag_list_html %>
             </td>

app/views/uploads/index.html.erb

@@ -16,7 +16,7 @@
         <% @uploads.each do |upload| %>
           <tr>
             <td>
-              <%= PostPresenter.preview(upload.post, tags: "user:#{upload.uploader_name}", show_deleted: true) %>
+              <%= PostPresenter.preview(upload.post, tags: "user:#{upload.uploader.name}", show_deleted: true) %>
             </td>
             <td class="col-expand upload-info">
               <span class="info">
@@ -62,7 +62,7 @@
             </td>
             <td>
               <%= link_to_user upload.uploader %>
-              <%= link_to "»", uploads_path(search: params[:search].merge(uploader_name: upload.uploader_name)) %>
+              <%= link_to "»", uploads_path(search: params[:search].merge(uploader_name: upload.uploader.name)) %>
               <br><%= time_ago_in_words_tagged  upload.created_at %>
             </td>
             <td class="col-normal">

app/views/user_feedbacks/show.html.erb

@@ -18,5 +18,5 @@
 <%= render "secondary_links" %>
 
 <% content_for(:page_title) do %>
-  Feedback - <%= @user_feedback.user_name %> - <%= Danbooru.config.app_name %>
+  Feedback - <%= @user_feedback.user.name %> - <%= Danbooru.config.app_name %>
 <% end %>

app/views/user_mailer/forum_notice.html.erb

@@ -2,7 +2,7 @@
 
 <% @forum_posts.each do |forum_post| %>
   <p>
-    <strong><%= forum_post.creator_name %> said:</strong>
+    <strong><%= forum_post.creator.name %> said:</strong>
   </p>
   <%= format_text(forum_post.body, base_url: root_url) %>
   <br>