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Quick Examples for LINQ Select And SelectMany and Differences

What is the Difference Between LINQ Select and SelectMany

Say we are having a Customer class and Order class

    class Customer

    {

        public string CusotmerName { get; set; }

        public string CusotmerCode { get; set; }

        public string CusotmerStatus { get; set; }

        public List<Order> OrderList { get; set; }

 

        public Customer(string pCusotmerName, string pCusotmerCode, string pCusotmerStatus, List<Order> pOrderList)

        {

            CusotmerName = pCusotmerName;

            CusotmerCode = pCusotmerCode;

            CusotmerStatus = pCusotmerStatus;

            OrderList = pOrderList;

        }

    }

 

 

    class Order

    {

        public int OrderNumber { get; set; }

        public DateTime OrderDate { get; set; }

        public string OrderStatus { get; set; }

 

        public Order(int pOrderNumber, DateTime pOrderDate, string pOrderStatus)

        {

            OrderNumber = pOrderNumber;

            OrderDate = pOrderDate;

            OrderStatus = pOrderStatus;

        }

    }

 

A Customer may generate any number of orders

In the following Line we do have a List of customers who are having the list of orders he / she has created inside the Customer Class

 

public List<Order> AllOrdersList = new List<Order>();

 

The question is if we want to see all the orders (only) for particular set of Customers

 

Select in LINQ will help you only to some extent

 

Let's see how it is

 

Let's generate sample data for 3 customers

 

List<Customer> LstCustomer = new List<Customer>()

            {

                new Customer("Cust 1","CUS1","Active",new List<Order>()

                {

                    new Order(100, DateTime.Now, "New"),

                    new Order(101, DateTime.Now.AddDays(-2), "InProgress"),

                    new Order(102, DateTime.Now, "New"),

                    new Order(103, DateTime.Now.AddDays(-10), "Complete")

                }),

 

 

                new Customer("Cust 2","CUS2","Active",new List<Order>()

                {

                    new Order(120, DateTime.Now, "New"),

                    new Order(121, DateTime.Now.AddDays(-2), "InProgress"),

                    new Order(122, DateTime.Now, "New"),

                    new Order(123, DateTime.Now.AddDays(-10), "Complete")

                }),

 

 

                new Customer("Cust 3","CUS3","InActive",new List<Order>()

                {

                    new Order(130, DateTime.Now, "OnHold"),

                    new Order(131, DateTime.Now.AddDays(-2), "InProgress"),

                    new Order(132, DateTime.Now, "OnHold"),

                    new Order(133, DateTime.Now.AddDays(-10), "Complete")

                })

            };

 

 

Now executing the following query

 

var selectResult = LstCustomer.Select(X => X.OrderList);

 

As a output you will get a list of lists

i.e. List<List<Order>>

 

// To dig deeper in this

 

// We are implementing Select Many in this

 

var selectManyResult = LstCustomer.SelectMany(X => X.OrderList);

 

// The output is awesome, as this is returning the list of Orders alone

 

           

 // Let's add more filters to this

 // Getting only the "New" orders

 

 var selectManyResul2 = LstCustomer

     .SelectMany(X => X.OrderList)

     .Where(X => X.OrderStatus == "New");

 

 

 // Adding more filters

 

 // Getting the Active Customers and

 // Getting only the "New" orders from those

 

 var selectManyResult3 = LstCustomer

     .Where(X => X.CusotmerStatus == "Active")

     .SelectMany(X => X.OrderList)

     .Where(X => X.OrderStatus == "New");

 

I think this has helped you to learn the difference between Select and SelectMany,

 

The source code is available in the following link

https://github.com/oneananda/C_Sharp_Examples/blob/main/LINQ_Examples/LINQ_Select_Vs_SelectMany.cs

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