Creating A Fluent API In C#.NET

Introduction

 

In this article we will look at creating a Fluent API class in C#.NET. In a Fluent API, we can link together different functionalities to get a particular result. We see this used many times in Entity Framework Core and when manipulating List<T> type of items using lambda expressions.

Creating the Fluent API class

 

We will create a simple employee class using Visual Studio 2019 Community edition as below,

namespace FluentAPiExample
{
    public class Employee
    {
        public int ID;
        public string Name;
        public string Location;
        public int age;
    }
}

Next, we will build the Interface for the Fluent API class as below,

using System.Collections.Generic;

namespace FluentAPiExample
{
    public interface IEmpDetails
    {
        IEmpDetails LoadEmployees();
        IEmpDetails FilterByLocation(string location);
        IEmpDetails FilterByAge(int age);
        List<Employee> GetData();
        List<Employee> Employees { get; set; }
    }
}

Finally, we implement the Interface as below,

using System.Collections.Generic;
using System.Linq;

namespace FluentAPiExample
{
    public class EmpDetails : IEmpDetails
    {
        public List<Employee> Employees { get; set; }

        public IEmpDetails LoadEmployees()
        {
            Employees = new List<Employee>() {  new Employee { ID = 1, Name = "John Doe", age = 25, Location = "Toronto" },
                                                new Employee { ID = 2, Name = "Jane Doe", age = 30, Location = "Toronto" },
                                                new Employee { ID = 3, Name = "Jana Doe", age = 35, Location = "Montreal" },
                                                new Employee { ID = 4, Name = "Mike Doe", age = 40, Location = "Montreal" },
                                                new Employee { ID = 5, Name = "Sam Doe", age = 45, Location = "Toronto" }
            };
            return this;

        }
        public IEmpDetails FilterByLocation(string location)
        {
            Employees = Employees.Where(s => s.Location == location).ToList();
            return this;
        }
        public IEmpDetails FilterByAge(int age)
        {
            Employees = Employees.Where(s => s.age <= age).ToList();
            return this;
        }

        public List<Employee> GetData()
        {
            return Employees;
        }

    }
}

Here you can see that every function returns the existing class in order to create a Fluent API chain. However, the final function “GetData” returns the main expected value.

 

Creating the Client function

 

Now we can use the Fluent API class as below,

using System;

namespace FluentAPiExample
{
    class Program
    {
        static void Main(string[] args)
        {

            // Using all filter options
            var emps = new EmpDetails().LoadEmployees().FilterByLocation("Montreal").FilterByAge(50).GetData();

            foreach(var emp in emps)
            {
                Console.WriteLine($"Employee details are {emp.ID},{emp.Name},{emp.Location},{emp.age}");
            }

            // Using one filter option
            var empsCityOnly = new EmpDetails().LoadEmployees().FilterByLocation("Toronto").GetData();

            foreach (var emp in empsCityOnly)
            {
                Console.WriteLine($"Employee details are {emp.ID},{emp.Name},{emp.Location},{emp.age}");
            }

            Console.ReadKey();
        }
    }
}

In the above example, you can see that we can use the filters as per our requirement and get the below output,

 

 

Summary

 

In this article, we have looked at creating a Fluent API class. This is especially useful when we want to create a chain of commands and allow the client to apply these as required.