first of all, this is a must-have for all serious about using Yii2.
the book is full of good advice and good code. too bad, in this first edition, is also full of little 'mistakes'. i reported all that i found to the publisher, so i hope next edition will be less error-ridden.
none of this error is serious, if you know php. some are simply typos. some are missing ' or closing parenthesis.
i highly recommend this book