linq join and count

I'm new to Linq and was wondering how I would go about obtaining a List of Customer Id, and a count of their transactions 

public class Transaction
{
    public int TransactionId {get; set;}
    public int CustomerId {get; set;}   
}


public class Customer
{
    public int ID {get; set;}
    public string Name {get; set;}
    public string Surname {get; set;}
}

I think I need to join customers with transactions but not too sure how I would get the count.

    var query  =    (from c  in customers
                    join t in transactions on c.ID equals t.CustomerId
Jon Skeet
people
quotationmark

saj's answer will only work if every customer has a transaction. Instead, it would be better to use a group join starting with Customer, and count the result:

var query = from customer in customers
            join transaction in transactions
              on customer.Id equals transaction.CustomerId
              into customerTransactions
            select new { customer.Id, Count = customerTransactions.Count() };

people

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