Reddit mentions of The Object-Oriented Thought Process (Developer's Library)

The Object-Oriented Thought Process - Matt Weisfeld

This is considered the golden standard for general OOP design, in my region.

These are both a part of programming outside of Unity as well. So you don't really need a Unity book.

My personal suggestion would not be to pick up something specifically aimed at Unity, instead pick up a C# book. You will learn more about the language and therefore increase your ability to code in Unity. You will also be able to write programs outside of Unity. As good as Unity can be for learning some of the basics of programming, it's tutorials barely scrape the surface of the language it uses or broader programming techniques. They are more focused on showing you features of Unity than features of the language. Having a better understanding of language and of programming in general, will allow you to do a lot more than most can in Unity. It will give you a better understanding of what you are doing as well.

Object pooling is quite simple and there are lots of free tutorials online for it. With a bit more knowledge you would probably be able to figure it out yourself, I certainly wouldn't see it as a technique to buy a book about.

Just in case you are unaware, as I was when I learnt Unity, objects are not a concept unique to Unity. They are more a feature of the language Unity uses. C# is one of many object orientated languages. Before jumping into design patterns it would be a good idea to get a good grasp of the pillars of OOP and how to design objects. This is the book I learnt from https://www.amazon.com/Object-Oriented-Thought-Process-Developers-Library/dp/0321861272/ref=sr_1_1?ie=UTF8&qid=1491986003&sr=8-1&keywords=object+oriented+design

However there are plenty of tutorials on the web about OOP as well.

There are plenty of design pattern books, many of the general design patters apply to games as well. You can't really recommend specific design patterns. The patterns you use will often depend on you or the people you work with. The goal of design patterns is to make your code more manageable by following conventions of design. However, if using a design pattern is making your code harder to understand then it is not fulfilling it's purpose. There are a few that are particularly good for particular parts of a program, but most of them come down to personal preference and what best suits you and the program you are creating.

Derek Banas has a series on youtube where he explains most of the popular patterns in a short amount of time.

This book will help you: Https://amzn.com/0321861272

OO helps to model your domain space; if you can't find any useful encapsulations of data and behaviour then you likely don't need it. In the code snippets you've provided, I could see the search_by_uid() method living in a helper/util file and being called by one of your objects with it's own arguments.

OO also helps prevent the use of global data. Global data is bad because not one entity has control over it which makes testing and debugging difficult. When properly designed, there is no global data in an OO model.

There are lots of other reasons to use OO (polymorphism, inheritance) but I think those might be the most important ones in your case. Check out the book https://www.amazon.com/Object-Oriented-Thought-Process-Developers-Library/dp/0321861272 for a nice overview.

http://www.amazon.com/Object-Oriented-Thought-Process-Edition-Developers/dp/0321861272

> Like a bunch of spaghetti

That might not all be your fault, I have no idea how good the codebase is! ;)

Two resource recommendations for you:

• The Object Oriented Thought Process. This book really helped me wrap my head around the core OOP concepts.
  
• Head First Design Patterns. A great intro to common patterns we use in software development. For example, the Singleton Pattern!
  
  One other thing I encourage you to do is to ask questions of the senior devs on the team. Try to find someone who you get along with and might be able to serve as an informal mentor. I know it is difficult to say "I don't know", but it is a lot better than floundering with a problem for a week. Good luck!

There is the Object Oriented Thought Process. I Haven't read it yet.