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.