{"id":50,"date":"2016-09-20T14:38:45","date_gmt":"2016-09-20T10:38:45","guid":{"rendered":"http:\/\/www.dobryakov.net\/blog\/?p=50"},"modified":"2016-09-20T14:38:45","modified_gmt":"2016-09-20T10:38:45","slug":"conditional-get-for-lists-nice-trick","status":"publish","type":"post","link":"https:\/\/www.dobryakov.net\/blog\/50\/","title":{"rendered":"Conditional GET for lists (nice trick)"},"content":{"rendered":"

Here is the nice trick to achieve Conditional GET request for lists (Index operation in classic REST terms). You know about this mechanism for single items (show operation): browser asks a resource for the first time, cache it’s last_modified value, and send “If-Modified-Since” header in the next request. A server checks database for resorce.update_at value, and responds “200 OK” with content as usual (if resource is newer), or responds with “304” without content<\/em> if resource was not<\/em> changed.<\/p>\n

You can see an economy for computing resources, traffic, parsing and so on. But how to implement this technique for lists? Where is no “updated_at” attribute for the lists…<\/p>\n

But don’t give up! Just get a newer<\/em> resourse in the list, and use it’s “updated_at” attribute.<\/p>\n

Here is an example for Ruby on Rails:
\nupdated_at = models.max_by(&:updated_at).try(:updated_at) || Time.at(1)<\/code><\/p>\n

The last part is a trick for empty lists. Easy!<\/p>\n

Caveats: it will not work when you destroy a model from collection by real deleting from the database, because the newer<\/em> “updated_at” value will not change or even becomes early. Browser will not get actual (changed) content. Use Paranoid gem (or mark it as something like ‘is_deleted’) instead, or switch to ETag.<\/p>\n","protected":false},"excerpt":{"rendered":"

Here is the nice trick to achieve Conditional GET request for lists (Index operation in classic REST terms). You know about this mechanism for single items (show operation): browser asks a resource for the first time, cache it’s last_modified value, and send “If-Modified-Since” header in the next request. A server checks database for resorce.update_at value, … Continue reading “Conditional GET for lists (nice trick)”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[3,12,15,18,21],"class_list":["post-50","post","type-post","status-publish","format-standard","hentry","category-uncategorized","tag-ajax","tag-http","tag-nginx","tag-rest","tag-spa"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t