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.
![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.