Question

I’m trying to rewrite some old SQL into LINQ to SQL. I have a sproc with a GROUP BY WITH ROLLUP but I’m not sure what the LINQ equivalent would be. LINQ has a GroupBy but it doesn’t look like it supports ROLLUP.

A simplified example of the results I’m trying to get would be something like this:

+-----------+---------------+--------------------+
|   City    |  ServicePlan  |  NumberOfCustomers |
+-----------+---------------+--------------------+
| Seattle   |  Plan A       |                 10 |
| Seattle   |  Plan B       |                  5 |
| Seattle   |  All          |                 15 |
| Portland  |  Plan A       |                 20 |
| Portland  |  Plan C       |                 10 |
| Portland  |  All          |                 30 |
| All       |  All          |                 45 |
+-----------+---------------+--------------------+

Any ideas on how I could get these results using LINQ to SQL?

Answer 1

I figured out a much simpler solution. I was trying to make it way more complicated than it needed to be. Rather than needing 3-5 classes/methods I only need one method.

Basically, you do your sorting and grouping yourself and then call WithRollup() to get a List<> of the items with sub-totals and a grand total. I couldn’t figure out how to generate the sub-totals and grand total on the SQL side so those are done with LINQ to Objects. Here’s the code:

/// <summary>
/// Adds sub-totals to a list of items, along with a grand total for the whole list.
/// </summary>
/// <param name="elements">Group and/or sort this yourself before calling WithRollup.</param>
/// <param name="primaryKeyOfElement">Given a TElement, return the property that you want sub-totals for.</param>
/// <param name="calculateSubTotalElement">Given a group of elements, return a TElement that represents the sub-total.</param>
/// <param name="grandTotalElement">A TElement that represents the grand total.</param>
public static List<TElement> WithRollup<TElement, TKey>(this IEnumerable<TElement> elements,
    Func<TElement, TKey> primaryKeyOfElement,
    Func<IGrouping<TKey, TElement>, TElement> calculateSubTotalElement,
    TElement grandTotalElement)
{
    // Create a new list the items, subtotals, and the grand total.
    List<TElement> results = new List<TElement>();
    var lookup = elements.ToLookup(primaryKeyOfElement);
    foreach (var group in lookup)
    {
        // Add items in the current group
        results.AddRange(group);
        // Add subTotal for current group
        results.Add(calculateSubTotalElement(group));
    }
    // Add grand total
    results.Add(grandTotalElement);

    return results;
}

And an example of how to use it:

class Program
{
    static void Main(string[] args)
    {
        IQueryable<CustomObject> dataItems = (new[]
        {
            new CustomObject { City = "Seattle", Plan = "Plan B", Charges = 20 },
            new CustomObject { City = "Seattle", Plan = "Plan A", Charges = 10 },
            new CustomObject { City = "Seattle", Plan = "Plan B", Charges = 20 },
            new CustomObject { City = "Seattle", Plan = "Plan A", Charges = 10 },
            new CustomObject { City = "Seattle", Plan = "Plan A", Charges = 10 },
            new CustomObject { City = "Seattle", Plan = "Plan A", Charges = 10 },
            new CustomObject { City = "Portland", Plan = "Plan A", Charges = 10 },
            new CustomObject { City = "Portland", Plan = "Plan A", Charges = 10 },
            new CustomObject { City = "Portland", Plan = "Plan C", Charges = 30 },
            new CustomObject { City = "Portland", Plan = "Plan C", Charges = 30 },
            new CustomObject { City = "Portland", Plan = "Plan C", Charges = 30 }
        }).AsQueryable();

        IQueryable<CustomObject> orderedElements = from item in dataItems
                                                   orderby item.City, item.Plan
                                                   group item by new { item.City, item.Plan } into grouping
                                                   select new CustomObject
                                                   {
                                                       City = grouping.Key.City,
                                                       Plan = grouping.Key.Plan,
                                                       Charges = grouping.Sum(item => item.Charges),
                                                       Count = grouping.Count()
                                                   };

        List<CustomObject> results = orderedElements.WithRollup(
            item => item.City,
            group => new CustomObject
            {
                City = group.Key,
                Plan = "All",
                Charges = group.Sum(item => item.Charges),
                Count = group.Sum(item => item.Count)
            },
            new CustomObject
            {
                City = "All",
                Plan = "All",
                Charges = orderedElements.Sum(item => item.Charges),
                Count = orderedElements.Sum(item => item.Count)
            });

        foreach (var result in results)
            Console.WriteLine(result);

        Console.Read();
    }
}

class CustomObject
{
    public string City { get; set; }
    public string Plan { get; set; }
    public int Count { get; set; }
    public decimal Charges { get; set; }

    public override string ToString()
    {
        return String.Format("{0} - {1} ({2} - {3})", City, Plan, Count, Charges);
    }
}