內容簡介
Gravity Forms 已經有內建的重複提交防止技術，包括您表單中的字段設置為「不允許重複」，避免同一表單中使用相同字段值的數據多次提交。使用此設置是一種可靠的方法來避免重複提交，但它要求您在表單中擁有一個被視為每次提交的唯一數據來源的字段。
此外掛可幫助您實現相同的概念，而無需在表單中啟用「不允許重複」設置，它會動態添加一個包含隨機令牌的隱藏輸入框，並檢查接收到的 POST 請求的令牌值，以避免重複提交。
這將阻止接受相同的 POST 請求來創建條目，例如在單擊瀏覽器的「返回」或「刷新」按鈕或在移動設備上還原瀏覽器選項卡時，某些瀏覽器將發送的請求。
重複的 POST 請求聯負責大多數重複（如果不是全部的話），因此使用此外掛可消除或大幅減少接收到重複數據的機會。
總結來說，使用流程如下：
啟用外掛後，每個表單都會包含一個值為隨機令牌的隱藏輸入框。
當 Gravity Forms 處理接收到的 POST 請求時，GF 不允許重複會檢查此 POST 請求是否包含令牌，以及令牌值是否已在與 POST 請求關聯的表單中的現有條目中使用過。
如果該令牌為空或任何表單條目中已經使用過令牌值，GF 不允許重複會觸發驗證錯誤，以中止提交。
表單將顯示驗證錯誤消息，其中包含指向表單頁面的鏈接，建議用戶單擊該鏈接以開始新的提交。
在某些情況下，用戶可能會忽略驗證消息，並僅單擊提交按鈕，阻止此訪問者的行為不在此外掛功能範圍內。
換句話說，此外掛旨在阻止自動重新發送相同的 POST 請求數據，而不是阻止訪問者自願啟動的提交。
需求
PHP 7.0 或更高版本。
WordPress 4.9 或更高版本。
Gravity Forms 2.5 或更高版本。
嵌入表單頁面必須從緩存中排除（如果您使用任何快取外掛或服務器緩存，請參閱下面的注意事項）。
使用方法
安裝並激活它，方式與安裝其他外掛一樣。
享受！無需設置！
關於快取的注意事項
此外掛功能基於動態生成的隨機令牌，因此從緩存中排除包含表單的頁面是必須的。如果您提供的是靜態版本的頁面以提供快取，則不僅限於此外掛，應該不要快取任何期望包含動態數據的頁面。
大多數快取外掛提供了緩存 URL 的排除方法，這是有原因的，要使用它。
還有一些 Web 主機提供商在服務器級別上使用緩存，並未為客戶提供排除實施URL的界面（例如WP Engine、Kinsta等），您仍可以請求主機支援人員為您添加排除。
您也可以使用 Fresh Forms ，在使用所支持的嵌入方法和快取外掛的情況下進行自動化的緩存排除（有關詳細信息，請參見 Fresh Forms 的說明）。
外掛標籤
開發者團隊
原文外掛簡介
Gravity Forms already has some built-in duplicate submission prevention techniques, including the No Duplicates setting for a field in your form, preventing the same field value from being used multiple times for the same form. Using this setting is a rock solid approach to avoid duplicate submissions, but it requires having a field in your form that you can consider as a source of unique data per submission.
This add-on helps using the same idea, without requiring having a field to enable the No Duplicates setting, by dynamically adding a hidden input with a random token to the form, and checks the POST request received for this token value to prevent duplicate submissions.
This will stop identical POST requests from being accepted for entry creation, like the ones that some browsers will send when the browser back or refresh buttons are clicked or when browser tabs are restored in mobile devices.
Limitations
If for any reason the visitor manually fills the form with the same information, and submits it again, blocking this visitor’s behavior is not within the scope of this plugin functionality.
To put in another way, the add-on is intended to block automated resend of the same POST request data, it doesn’t block submissions voluntarily initiated by the visitor.
If your site is still receiving repeated POST requests created before enabling the add-on, therefore not containing the token field, you would still receive duplicates for these entries. There’s no way for the add-on to be able stop duplicates for requests created before enabling the add-on.
How it works:
When the add-on is enabled a hidden input with a random token as value is added to each form dynamically in the front-end.
When a POST request is received and handled by Gravity Forms, GF No Duplicates checks if this POST request has the token and if its value was used already in an existing entry for the form tied to the POST request.
If the token parameter exists but is empty or there’s any form entry where the token value was used already, GF No Duplicates stops the submission.
The form is replaced with an error message, which contains a link to the form page, suggesting the visitor to click the link to start a fresh new submission.
Requirements
PHP 7.0 or higher.
WordPress 4.9 or higher.
Gravity Forms 2.5 or higher.
The page where the form is embedded must be excluded from cache (if you use any caching plugin or server cache, see note below).
Usage
Install and activate it as you do with any other plugin.
Enjoy!
Optionally, you can customize the duplicate submission message shown to users from the settings page or using a filter (see the FAQ).
Note about Caching
The add-on functionality relies on a random token generated dynamically, so for obvious reasons caching the page where your form is embedded would prevent the add-on from working as expected. This is not a limitation of the add-on but the expected if you’re serving a static version of your page, which is the only reason to cache a page, you shouldn’t never cache pages where you expect dynamic data.
Most caching plugins provide you a way to exclude URLs from cache, this is for a reason, use it.
There are some web hosting providers using cache at server level and not providing their customers with an interface to exclude URLs from cache (e.g. WP Engine, Kinsta, …), you can still ask your host support staff to add the exclusion for you.
You can also use Fresh Forms for automated cache exclusion if you use any of the embedding methods and caching plugins supported (see Fresh Forms description for more details).
