Mysql2::Error: Incorrect string value

the problem is caused by charset of your mysql server side. You can config manually like:

ALTER TABLE your_database_name.your_table CONVERT TO CHARACTER SET utf8

or drop the table and recreate it like:

rake db:drop
rake db:create
rake db:migrate

references:

https://stackoverflow.com/a/18498210/2034097

https://stackoverflow.com/a/16934647/2034097

UPDATE

the first command only affect specified table, if you want to change all the tables in a database, you can do like

ALTER DATABASE databasename CHARACTER SET utf8 COLLATE utf8_general_ci;

reference:

https://stackoverflow.com/a/6115705/2034097

I managed to store emojis (which take up 4 bytes) by following this blog post:

Rails 4, MySQL, and Emoji (Mysql2::Error: Incorrect string value error.)

You might think that you’re safe inserting most utf8 data in to mysql when you’ve specified that the charset is utf-8. Sadly, however, you’d be wrong. The problem is that the utf8 character set takes up 3 bytes when stored in a VARCHAR column. Emoji characters, on the other hand, take up 4 bytes.

The solution is in 2 parts:

Change the encoding of your table and fields:

ALTER TABLE `[table]` 
  CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_bin,
MODIFY [column] VARCHAR(250)
    CHARACTER SET utf8mb4 COLLATE utf8mb4_bin

Tell the mysql2 adapter about it:

development:
  adapter: mysql2
  database: db
  username: 
  password:
  encoding: utf8mb4
  collation: utf8mb4_unicode_ci

Hope this helps someone!

Then I had to restart my app and it worked. Please note that some emojis will work without this fix, while some won't:

• ➡️ Did work
• Did not work until I applied the fix described above.

You can use a migration like this to convert your tables to utf8:

class ConvertTablesToUtf8 < ActiveRecord::Migration
  def change_encoding(encoding,collation)
    connection = ActiveRecord::Base.connection
    tables = connection.tables
    dbname =connection.current_database
    execute <<-SQL
      ALTER DATABASE #{dbname} CHARACTER SET #{encoding} COLLATE #{collation};
    SQL
    tables.each do |tablename|
      execute <<-SQL
        ALTER TABLE #{dbname}.#{tablename} CONVERT TO CHARACTER SET #{encoding} COLLATE #{collation};
      SQL
    end
  end

  def change
    reversible do |dir|
      dir.up do
        change_encoding('utf8','utf8_general_ci')
      end
      dir.down do
        change_encoding('latin1','latin1_swedish_ci')
      end
    end
  end
end