prøv denne variant af db.php for at angive defaultSchema
return [
'class' => 'yii\db\Connection',
'dsn' => 'pgsql:host=localhost;dbname=db_name',
'username' => 'db_username',
'password' => 'db_password',
'charset' => 'utf8',
'schemaMap' => [
'pgsql'=> [
'class'=>'yii\db\pgsql\Schema',
'defaultSchema' => 'public' //specify your schema here
]
], // PostgreSQL
];