Grouping queries

Question

I have a list of Options. From that list:

• First I want to get only Drink (the where clause).

• Then I want to group them by their SortOrder (range of 100).

• I can stop there and loop through the items and create checkboxes for each items. But I got a requirement that if the OptionGroupName=Alcohol then I need to create radio list instead of checkboxes.

Here's the code that does grouping using Linq:

Option[] options = GetOptions();
var groupedOptions = from option in options
 where option.OptionType == OptionType.Drinks
 group option by option.SortOrder / 100 into grouped
 select new { 
 SortOrderGroup = grouped.Key,
 GroupName = grouped.FirstOrDefault().OptionGroupName
 ,SubGroup= grouped
};

Here's the JSON I get. That's what I want:

So now I can check on client-side if GroupName="Alcohol" generate radio buttons else generate checkboxes.

[
 {
 "SortOrderGroup": 3,
 "GroupName": "Soft",
 "SubGroup": [
 {
 "OptionId": 1,
 "DisplayName": "Coke",
 "OptionType": 2,
 "SortOrder": 300,
 "OptionGroupName": "Soft"
 },
 {
 "OptionId": 2,
 "DisplayName": "Pepsi",
 "OptionType": 2,
 "SortOrder": 301,
 "OptionGroupName": "Soft"
 },
 {
 "OptionId": 3,
 "DisplayName": "Sprite",
 "OptionType": 2,
 "SortOrder": 302,
 "OptionGroupName": "Soft"
 }
 ]
 },
 {
 "SortOrderGroup": 4,
 "GroupName": "Fruit",
 "SubGroup": [
 {
 "OptionId": 4,
 "DisplayName": "Apple Juice",
 "OptionType": 2,
 "SortOrder": 406,
 "OptionGroupName": "Fruit"
 },
 {
 "OptionId": 1,
 "DisplayName": "Orange Juice",
 "OptionType": 2,
 "SortOrder": 400,
 "OptionGroupName": "Fruit"
 }
 ]
 },
 {
 "SortOrderGroup": 5,
 "GroupName": "Alcohol",
 "SubGroup": [
 {
 "OptionId": 2,
 "DisplayName": "Wine",
 "OptionType": 2,
 "SortOrder": 501,
 "OptionGroupName": "Alcohol"
 },
 {
 "OptionId": 3,
 "DisplayName": "Beer",
 "OptionType": 2,
 "SortOrder": 502,
 "OptionGroupName": "Alcohol"
 },
 {
 "OptionId": 4,
 "DisplayName": "Rum",
 "OptionType": 2,
 "SortOrder": 520,
 "OptionGroupName": "Alcohol"
 }
 ]
 }
]

Answer 1

So we're looking at a LINQ query:

Option[] options = GetOptions();
var groupedOptions = from option in options
 where option.OptionType == OptionType.Drinks
 group option by option.SortOrder / 100 into grouped
 select new { 
 SortOrderGroup = grouped.Key,
 GroupName = grouped.FirstOrDefault().OptionGroupName
 ,SubGroup= grouped
};

You went with query syntax - let's see what the method syntax would look like:

var options = GetOptions(); // some IEnumerable - who cares that it's an array?
options.Where(option => option.OptionType == OptionType.Drinks)
 .GroupBy(option => option.SortOrder / 100)
 .Select(grouped => new 
 { 
 Grouping = grouped.Key, 
 Name = grouped.FirstOrDefault().OptionGroupName),
 SubGroup = grouped 
 });

The FirstOrDefault() call will return a null when grouped has no items - that's not really a possibility here, but just because FirstOrDefault itself can return a null, accessing .OptionGroupName on it looks like it's asking for a NullReferenceException. It would be better to use .First() here, because you know a group only exists when it has at least one item...

...but then, you already have an OptionGroupName for each item - why bother selecting the .First at all?

I'd probably write your query like this:

options.Where(option => option.OptionType == OptionType.Drinks)
 .GroupBy(option => new
 {
 SortOrder = option.SortOrder / 100, // integer division
 GroupName = option.OptionGroupName
 })
 .Select(grouping => new 
 { 
 SortOrder = grouping.Key.SortOrder, 
 Name = grouping.Key.GroupName,
 SubGroup = grouping 
 });

---

Notice I don't care what type GetOptions() is returning - all I'm interested in, is that whatever it's returning implements IEnumerable<T> so that I can LINQ over it - and the plural name is all I need to see to infer I'm dealing wiht an IEnumerable<T> :)

GetOptions shouldn't be returning an array (a concrete type) - it should return an abstraction - IEnumerable<T> in this case.

• gbs: The GetOptions is a 3rd party service call that returns an Array. I will try out your suggestion.