Lars-Erik KindbladSenior ConsultantBlog: kindblad.com

The Fluent Interface Pattern

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A common problem in most software projects

Technical debts increases over time and the code gets harder and harder to maintain and add features to

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Feature delivery for most projects

Time

Feat

ures

Del

iver

ed

Technical debt

Complex and messy codeCode and logic is duplicatedNo common coding standard

No strict architecture

++

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Ideal Feature Delivery

Time

Feat

ures

Del

iver

ed

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How to reach ideal delivery?

Software development is complex Not a single solution but a mix of many different things

• Write a lot of code• Important to understand the business model• Readable & maintainable code over fancy code• Simplicity over complexity• Decide on a common coding standard• Reuse code instead of code duplication• Create a project framework with common code and logic• Design Patterns – follow generic solutions to commonly occurring problemso 100s of design patterns exists

– Factory Pattern, MVC Pattern, Command Pattern, Fluent Interface Pattern etc.

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The Fluent Interface Pattern

One of many design patterns that can contribute to a better code base

Fluent Interfaces makes the code easier to read and easier to use due to a simpler API that requires less code

Consists of 2 principles:• Method chaining - Traditional code requires one line per command, method

chaining allows multiple commands per line• More readable API – The code can be read like a sentence. Optional as it

requires more typing due to longer names and more code to write

Popular to use in frameworks: Moq, Fluent Nhibernate, FluentData etc.

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Fluent Interface Code:

Example – Find a person

Traditional Code:

Or:

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A more readable Fluent Interface

Or:

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Designing Fluent Interfaces - Method vs. Property

Use a method when having toaccept one or more values

Use a property when not havingto accept any values

Use a method to finish the call

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Traditional Code

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Fluent Interface Code

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Example #2 – A List of Persons

Traditional Code:

Fluent Code:

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Traditional Code

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Fluent Interface Step 1: Add Gateway Pattern

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Step 2: Add Fluent Interface Pattern

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Examples from other Frameworks

Moq:

FluentData:

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When to use Fluent Interfaces

Anywhere where it makes the code easier to read and easier to use Typically in methods that are often invoked Together with the Gateway Pattern to hide complex 3rd party code or

legacy code Frameworks

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