Book Image

Scala Functional Programming Patterns

By : Atul S. Khot
Book Image

Scala Functional Programming Patterns

By: Atul S. Khot

Overview of this book

Scala is used to construct elegant class hierarchies for maximum code reuse and extensibility and to implement their behavior using higher-order functions. Its functional programming (FP) features are a boon to help you design “easy to reason about” systems to control the growing software complexities. Knowing how and where to apply the many Scala techniques is challenging. Looking at Scala best practices in the context of what you already know helps you grasp these concepts quickly, and helps you see where and why to use them. This book begins with the rationale behind patterns to help you understand where and why each pattern is applied. You will discover what tail recursion brings to your table and will get an understanding of how to create solutions without mutations. We then explain the concept of memorization and infinite sequences for on-demand computation. Further, the book takes you through Scala’s stackable traits and dependency injection, a popular technique to produce loosely-coupled software systems. You will also explore how to currying favors to your code and how to simplify it by de-construction via pattern matching. We also show you how to do pipeline transformations using higher order functions such as the pipes and filters pattern. Then we guide you through the increasing importance of concurrent programming and the pitfalls of traditional code concurrency. Lastly, the book takes a paradigm shift to show you the different techniques that functional programming brings to your plate. This book is an invaluable source to help you understand and perform functional programming and solve common programming problems using Scala’s programming patterns.
Table of Contents (19 chapters)
Scala Functional Programming Patterns
Credits
About the Author
Aknowledgement
About the Reviewers
www.PacktPub.com
Preface
Index

Hibernate's lazy loading


Hibernate exposes persistence-related database access via an object API. A Java class is mapped to a database table. A parent having many children is mapped as shown in the following code:

@Entity
public class Parent {
… 
@OneToMany(mappedBy = "parent")
private Set<Child> children;
…
}  
@Entity
public class Child {
… 
@ManyToOne
@JoinColumn(name = "parent_id")
private Parent parent;
… 
}

This maps the following table structure:

Figure 4.3: Proxying in Hibernate

The children are, by default, lazy loaded. This holds true for any mapped members that are collections. You may not need them all the time you load the parent. If you do, you can load them as needed. The set is actually a PersistenceSet, a proxy. The catch is that this is not completely transparent though. You need to have a hibernate session active to load the children. Otherwise, you get a LazyInitializationException.

Why is this done? The children may have children of their own. The object graph, parent...