Mysql2::Error: Incorrect string value

Recently, Got some errors about “Incorrect string value” in my site, Since the site is mostly used by Chinese, I thought it caused by incorrect database encoding. After check the database, All tables are set in UTF-8. Finally I found there’re some emoji in the data that user posted. This needs utf8mb4 encoding. So use

  ALTER TABLE table_name CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_bin;

resolved it.

The problem might be complicate in some case, here is a nice article that introduced how to support emoji in database.