Something I find really useful in development, and that isn't unique to Yii2, is migrations. These are blocks of code that explain what should be done to a database in order to add new schema elements or change them is some way. Sometimes there's an issue with a migration and this post looks to cover the "no such file or directory" error I received today.
On running my migration to kick off my project I received this message:
Exception 'yii\db\Exception' with message 'SQLSTATE[HY000]  No such file or directory'
That's not altogether helpful as I know all the files are correct and there's definitely a database server (MariaDB) on this system. I checked my configuration, all seemed to be in order, and resorted to searching the web. This post on Stackoverflow had the solution - change my database host from localhost to 127.0.0.1. I've not had to do this before but I gave it a go. Problem solved!
My config now looks like this:
return [ 'class' => 'yii\db\Connection', 'dsn' => 'mysql:host=127.0.0.1;dbname=devdb', 'username' => 'development', 'password' => 'HiddenFromYou', 'charset' => 'utf8', ]