How to use Join in LINQ with example.

 In LINQ, you can use the join clause to combine two sequences based on a common key. The join clause works similar to a SQL join statement.

Here's an example of how to apply join in LINQ:

// create a collection of objects
List<Customer> customers = new List<Customer>
{
    new Customer { Id = 1, Name = "Alice", City = "New York" },
    new Customer { Id = 2, Name = "Bob", City = "Los Angeles" },
    new Customer { Id = 3, Name = "Charlie", City = "Chicago" },
    new Customer { Id = 4, Name = "David", City = "New York" },
    new Customer { Id = 5, Name = "Eva", City = "Los Angeles" }
};

List<Order> orders = new List<Order>
{
    new Order { Id = 1001, CustomerId = 1, Amount = 100 },
    new Order { Id = 1002, CustomerId = 2, Amount = 200 },
    new Order { Id = 1003, CustomerId = 2, Amount = 300 },
    new Order { Id = 1004, CustomerId = 4, Amount = 150 },
    new Order { Id = 1005, CustomerId = 5, Amount = 250 }
};

// join customers and orders by customer id
var query = from c in customers
            join o in orders on c.Id equals o.CustomerId
            select new { CustomerName = c.Name, OrderAmount = o.Amount };

// iterate through the result
foreach (var item in query)
{
    Console.WriteLine("Customer: " + item.CustomerName + ", Order Amount: " + item.OrderAmount);
}

In this example, we first create two collections of objects: customers and orders, with Customer and Order classes respectively. Each Order has a CustomerId property that corresponds to the Id property of a Customer.

We then use the join keyword in a LINQ query to join the customers and orders collections on the CustomerId and Id properties respectively. This creates a new sequence of objects that combines data from both collections.

We then use the select keyword to create a new anonymous type that contains the Name property of the Customer and the Amount property of the Order. This creates a new sequence of objects that contains only the data we want to see in the output.

Finally, we iterate through the result using a foreach loop and print out the CustomerName and OrderAmount properties of each object in the sequence.

The output of this code will be:

Customer: Alice, Order Amount: 100
Customer: Bob, Order Amount: 200
Customer: Bob, Order Amount: 300
Customer: David, Order Amount: 150
Customer: Eva, Order Amount: 250

As you can see, the join operation has combined the data from the customers and orders collections based on the CustomerId and Id properties, and the output shows the Name of each Customer and the Amount of their Order.