This example shows a complete but minimally annotated immutable class that is ready for use with the enhanced client: = Record.Builder. At a minimum you must specify a Other annotations are optional. These annotations are the same and work in the same way as the existing bean class annotations. An example using an inner-class of our immutable class ‘Record’ called ‘Builder’ would be = ).Īdd other standard DynamoDB enhanced client annotations as required. You must pass a parameter of ‘builder’ to the annotation with the value set to the builder class you use to build objects of your immutable class. The immutable class you create should only have getters, and there must be a static builder class that can be used to construct instances of it.Īdd the annotation to the immutable class. You may either follow the example below or create your own class. Step 1 : Annotate your existing immutable classįirst, create and annotate an immutable class that will map to records in your DynamoDB table. See our Java SDK Developer Guide for the details on how to manage the AWS Java SDK dependency in your project. For immutable object mapping support you must be using version 2.14.10 or later. Quick walk-through for mapping an immutable class Prerequisites:īefore getting started with mapping immutable classes, ensure your SDK dependency is up to date with all the latest released bug-fixes and features. While Immutable.js is inspired by Clojure, Scala, Haskell and other functional programming environments, it's designed to bring these powerful concepts to JavaScript, and therefore has an Object-Oriented API that closely mirrors that of ES2015 Array, Map, and Set. Now the enhanced client can work directly with the immutable classes with the addition of a just a few simple annotations. Instead, they were forced to work with bean objects and use elaborate workarounds, such as copying and transforming the objects read by the enhanced client or wrapping them in an opaque container. It is also typical to have a separate mutable ‘builder’ class to assist with collecting the initialization values for these properties.īefore this release, customers using immutable style objects had no way to directly map records they were reading and writing from their DynamoDB tables to these objects. Immutable objects in Java characteristically only have getters (and no setters) and are constructed by passing all their properties at once to the constructor. Immutability in Java is a commonly used style that allows developers to create classes that are side-effect free and therefore predictable in complex and multi-threaded applications. Previously, only mutable ‘Java bean’ style objects were supported. This does require that we track the reference that holds the state, but the whole problem has now been reduced to managing a single reference.We are pleased to announce that the enhanced DynamoDB client in the AWS SDK for Java 2.x now supports the mapping of immutable Java objects directly with records in your DynamoDB tables. If the application state hasn’t updated, it’ll be the same instance as before, and we don’t need do anything at all. Similarly, an immutable map, which can be used in place of most objects, would have methods to “set” properties that don’t actually set anything, but return a new object with the desired changes: var person = new ImmutableMap ( Inspired by strings and numbers behavior, it would have the following behavior: var arr = new ImmutableArray ( ) var v2 = arr. Instead, the arr reference has been updated to contain the number, and v2 contains the new length of arr. What is the value of v2? If arrays behaved consistently with strings and numbers, v2 would contain a new array with one element – the number 2 – in it. However, consider the following example using arrays: var arr = var v2 = arr. In JavaScript, strings and numbers are immutable by design. Can you even imagine an environment where evaluating the expression 2 + 3 changes the meaning of the number 2? It sounds absurd, yet we do this with our objects and arrays all the time. Strings are not the only immutable values built into JavaScript. The reason is that strings are immutable – they cannot change, we can only ever make new strings. In fact, no string methods change the string they operate on, they all return new strings. I think no one will be surprised to learn that the second line in no way changes the string in statement. var statement = "I am an immutable value" var otherStr = statement. If this seems strange, allow me to remind you that many of the values we use all the time are in fact immutable. An immutable value is the exact opposite – after it has been created, it can never change. In programming, we use the word to mean objects whose state is allowed to change over time. The text-book definition of mutability is liable or subject to change or alteration.
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