Return more than one result-CodePudding

I have a bug that I need more than one result from a foreach without creating a new collection in the method. I need to get rid of the foreach however I don`t know what LINQ method to use.

I have tried,

return basket.Items.SelectMany(
    item => item.Id == orderComplimentaryUtilities.Where(o => o.Id));

public static IEnumerable<OrderItem> WhichUtilitiesAreAlreadyInBasket(
    this 
    IEnumerable<OrderComplimentaryUtility.OrderComplimentaryUtility> 
            orderComplimentaryUtilities,
    Order basket)
{
    if (basket == null || orderComplimentaryUtilities == null)
    {
        return Enumerable.Empty<OrderItem>();
    }
    
    foreach (var orderComplimentaryUtility in orderComplimentaryUtilities)
    {
        return basket.Items.Where(item => item.Id == orderComplimentaryUtility.Id);
    }

    return Enumerable.Empty<OrderItem>();
}

CodePudding user response：

It appears that you are looking to join the data from two sequences (orderComplimentaryUtilities and basket), and return the data from basket where they match by id.

You can accomplish this with a LINQ join:

public static IEnumerable<OrderItem> WhichUtilitiesAreAlreadyInBasket(
    this IEnumerable<OrderComplimentaryUtility.OrderComplimentaryUtility> orderComplimentaryUtilities, 
    Order basket)
{
    if (basket == null || orderComplimentaryUtilities == null)
    {
        return Enumerable.Empty<OrderItem>();
    }
    
    var items = orderComplimentaryUtilities
                .Join(basket,
                      u => u.ID,
                      b => b.ID,
                      (u, b) => b);

    return items;
}

CodePudding user response：

You can use Contains if you separate out the ids into a collection:

var ids = orderComplimentaryUtility.Select(i => i.id).ToArray();
return basket.Items.Where(item => ids.Contains(item.Id));

If this is all in-memory, you could inline the Select into the Where clause, but that may not work if you're querying a SQL data source that cannot convert the Select into an IN clause.