Dependency Injection Lifetime: Transient

Introduction

Dependency injection is a design pattern that allows the creation of objects with their dependencies provided externally rather than being created inside the object itself. The lifetime of the dependency injected object determines how long the object will live and how often it will be created.

Transient lifetime is a type of lifetime in dependency injection that creates a new instance of the dependency for every time it is requested. In this article, we will discuss how transient lifetime works and answer common questions related to this topic.

How Transient Lifetime Works

In transient lifetime, a new instance of the dependency is created every time it is requested. This means that the object is not shared between multiple requests. For example, if a class is injected with a dependency that has a transient lifetime, every time the class is instantiated, the dependency will also be instantiated, and a new instance of the dependency will be created.

The following code snippet shows how to register a dependency with a transient lifetime in .NET Core:

“`
services.AddTransient();
“`

In this code, `services` is an instance of `IServiceCollection`, which is used to register dependencies. `IMyDependency` is the interface for the dependency, and `MyDependency` is the implementation of that interface. `AddTransient` method is used to register the `MyDependency` class with a transient lifetime.

Benefits of Transient Lifetime

There are several benefits to using a transient lifetime in dependency injection:

1. Memory efficient: Since a new instance is created every time the dependency is requested, it is memory-efficient. If the dependency is not used frequently, it will not take up unnecessary memory.

2. Flexible: Transient lifetime is flexible as it allows the dependency to be created every time it is requested. This means that the dependency can be changed at runtime if necessary.

3. Thread-safe: Since each request gets its own instance of the dependency, there is no risk of thread-safety issues. Each request has its independent dependencies, and there is no interference between them.

FAQs

Q1. When should we use a transient lifetime?

A1. A transient lifetime should be used when:

– The dependency is lightweight, and creating it every time is not expensive
– The dependency does not hold state and can be created easily

Q2. Are dependencies with a transient lifetime thread-safe?

A2. Yes, dependencies with a transient lifetime are thread-safe, as every request gets its independent instance of the dependency.

Q3. What is the difference between transient and singleton lifetime?

A3. The main difference between transient and singleton lifetime is that in a singleton lifetime, only one instance of the dependency is created, and that instance is shared between multiple requests. In contrast, in transient lifetime, a new instance of the dependency is created every time it is requested.

Q4. What happens if we inject a dependency with a transient lifetime into a singleton?

A4. If we inject a dependency with a transient lifetime into a singleton, every time the singleton is requested, the same instance of the dependency will be injected. This means that instead of getting a new instance of the dependency every time, we will get the same instance repeatedly.

Q5. How can we change the lifetime of a dependency?

A5. The lifetime of a dependency can be changed by changing the method used to register it. For example, to change the lifetime of a dependency from transient to singleton, we can use the following code:

“`
services.AddSingleton();
“`

This code changes the lifetime of the `MyDependency` class from transient to singleton.

Conclusion

Transient lifetime is a type of lifetime in dependency injection that creates a new instance of the dependency for every time it is requested. This article discussed how transient lifetime works and its benefits. We also answered some common questions related to it. Using transient lifetime appropriately can help improve the performance and memory efficiency of an application.