Loop an array with nested select LINQ

Question

I have the following data structure (just a exemplary visual representation):

list<customer>
{
    customer
    {
        name
        orders[]
        {
            order
            {
                quantity
                product
                {
                    price
                }
            }
            order
            {
                ...
            }
            order
            {
                ...
            }
    }
    customer
    {
        ...
    }
    customer
    {
        ...
    }
}

And I want to acquire the name of each Customer and the total sum of his orders (qty*product price). Now I have the following:

var sumEachCust = from c in customers
                  let sum = 0.0m
                  select new
                  {
                     c.Name,
                     sum =+ (from o in c.Orders
                             select o.Product.Price * o.Quantity).FirstOrDefault()
                  };

If the Customer object has more than one Order entry in its Orders[], then I want the sum of all the entries inside. But with this query I get the sum just for the first order.

If I make it this way:

var sumEachCust = from c in customers
                  let sum = 0.0m
                  from o in c.Orders
                  select new
                  {
                    c.Name,
                    sum =+ o.Product.Price * o.Quantity
                  };

then I will get the name as many times as there are order entities in the Orders[] property of the Customer object, and I don't want that.

Simply - just once name and sum of all orders.

James · Accepted Answer · 2014-09-29 09:28:26Z

8

from c in customers
select new
{
     Name = c.name,
     OrderTotal = c.orders.Sum(o => o.product.price * o.quantity)
}

If you really want to use let then here is how you would do that for this scenario

from c in customers
let sum = c.orders.Sum(o => o.product.price * o.quantity)
select new
{
    Name = c.name,
    OrderTotal = sum
}

edited Sep 29, 2014 at 9:28

answered Sep 29, 2014 at 9:13

James

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4 Comments

Milkncookiez Over a year ago

Works and is a really clean and simple solution! Thanks a lot! Nevertheless, could you give me an example using let and temporary variable in the query, since I was going that way and would like to see how to correctly use a nested select statement in this case?

James Over a year ago

@Milkncookiez see update, although you really don't need to use let at all here.

Milkncookiez Over a year ago

sorry, I wanted to ask about an example with a nested select, because for example, if I have to sum the orders of all customers together into one total sum (instead of summing the orders of each customer separately), then how would I do that? (given that I am not completely sure how to use the iteration logic of nested query).

James Over a year ago

@Milkncookiez to return the sum of all the records then you can simply do let sum = customers.Sum(x => x.orders.Sum(o => o.product.price * o.quantity)) - bare in mind this will result in a separate query though.

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