How does one sort a List of Tuples of two custom objects by a property in the first element, but if the first element is null, then use the second element's properties?

Question

How does one sort a List of Tuples of two custom objects by a property in the first element, but if the first element is null, then use the second element's properties?

Jonathan Howell 20

I have a list of Tuples with generic objects (List<Tuple<T?, T?>>). I am able to sort based on two properties from the objects in either the first or second element without an issue. The problem is that either the first or second element's object could be null. What I need to be able to do is sort on the first item by the two properties, but if the first item is null, then use the second item's same two properties. When I try to do this using a ternary operator it errors on the null item even after a null check.

More details:
The list contains comparison items.
The first item in the Tuple is the source item, the second is the target of the comparison.
If the source item does not have a match in the target, the second element in the tuple will be null.
If the target item does not have a match in the source, the first element in the tuple will be null.
The sort is done on two properties of each object which make them unique to the environment they are in.

Example: A list of products which has a category and name where the combination of those two items is unique.
I need the sort to put the items in each category together for readability. So if there is a category "Tools" with a product named "Hammer" which exists in the second element of the tuple, but has no match in the first (so it is null) it will be listed in order with the other category items of "Tools" from the first element. Not at the end by itself.

What I thought would work is the below, but it breaks if there is a null even with the null check. What can I do to get this to work?

I am also open to better ways of doing this if someone has a better idea.

List<Tuple<T?, T?>> allItems = comparisonList
                .OrderBy(x => x.Item1.GetType().GetProperty(sortPropA) is null ? x.Item2.GetType().GetProperty(sortPropA).GetValue(x.Item2) : x.Item1.GetType().GetProperty(sortPropA).GetValue(x.Item1))
                .ThenBy(x => x.Item1.GetType().GetProperty(sortPropB) is null ? x.Item2.GetType().GetProperty(sortPropB).GetValue(x.Item2) : x.Item1.GetType().GetProperty(sortPropB).GetValue(x.Item1))
                .ToList();

Anonymous

2023-05-24T07:05:49.89+00:00

Hi @Jonathan Howell , Welcome to Microsoft Q&A. Please give an example of data, I don't understand what you mean.
Jonathan Howell 20 Reputation points

2023-05-24T16:31:23.9166667+00:00
Hi @Anonymous , An example would be two lists of products.

Source list would be:
Product Category: Tools, Product Name: Hammer, Price: $20
Product Category: Tools, Product Name: Screwdriver, Price: $10
Product Category: Appliances, Product Name: Television, Price: $500
Product Category: Appliances, Product Name: Toaster, Price: $25

Target list would be:
Product Category: Tools, Product Name: Saw, Price: $30
Product Category: Tools, Product Name: Hammer, Price: $15
Product Category: Appliances, Product Name: Toaster, Price: $35
Product Category: Clothing, Product Name: Jacket, Price: $50

The way it is now I create three lists of tuples of objects List<Tuple<MyObject?, MyObject?>>. The first element is the source list items and the second is the target list items. If there is not a match there is null in the element with no match. The match is only done on the "category" and "name" properties. So we get the three lists that contain the following:

The first is items in the source list, but not the target, so we get the following in the first element and null in the second:
Product Category: Tools, Product Name: Screwdriver, Price: $10
Product Category: Appliances, Product Name: Television, Price: $500

The second list would be items in the target list, but not the source, so the first element would have null:
Product Category: Tools, Product Name: Saw, Price: $30
Product Category: Clothing, Product Name: Jacket, Price: $50

The third list would have items in both lists so it would have the following in the first two elements:
Product Category: Tools, Product Name: Hammer, Price: $20
Product Category: Appliances, Product Name: Toaster, Price: $25

With their matches in the second two elements:
Product Category: Tools, Product Name: Hammer, Price: $15
Product Category: Appliances, Product Name: Toaster, Price: $35

Once those three lists are created I merge them together.

What I want to do is be able to sort the list of tuples based on the "Category" then "Name" fields. I can do that for a single element, so say the first element, but if the second element is null it will not sort in the right order. I want the output to be like:

Row1: Element1: Product Category: Appliances, Product Name: Television, Price: $500
Row1: Element2: NULL
Row2: Element1: Product Category: Appliances, Product Name: Toaster, Price: $25
Row2: Element2: Product Category: Appliances, Product Name: Toaster, Price: $35
Row3: Element1: NULL
Row3: Element2: Product Category: Clothing, Product Name: Jacket, Price: $50
Row4: Element1: Product Category: Tools, Product Name: Hammer, Price: $20
Row4: Element2: Product Category: Tools, Product Name: Hammer, Price: $15
Row5: Element1: NULL
Row5: Element2: Product Category: Tools, Product Name: Saw, Price: $30
Row6: Element1: Product Category: Tools, Product Name: Screwdriver, Price: $10
Row6: Element2: NULL

What I tried was the following, but it is not working because of the null value in the object throwing an error when it tries to check for null (in the x.Item1.Category is null):

List<Tuple<MyObject?, MyObject?>> allItems = inBothLists.Concat(inSourceList).Concat(inTargetList) .OrderBy(x => x.Item1.Category is null ? x.Item2.Category.GetValue(x.Item2) : x.Item1.Category.GetValue(x.Item1)) .ThenBy(x => x.Item1.Name is null ? x.Item2.Name.GetValue(x.Item2) : x.Item1.Name.GetValue(x.Item1)) .ToList();

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Anonymous

2023-05-24T07:05:49.89+00:00

Hi @Jonathan Howell , Welcome to Microsoft Q&A. Please give an example of data, I don't understand what you mean.

Answer 1

Bruce (SqlWork.com) 77,686 Volunteer Moderator

you cannot access properties of null items. you must check if null first.

List<Tuple<MyObject?, MyObject?>> allItems = inBothLists.Concat(inSourceList).Concat(inTargetList)
     .OrderBy(x => x.Item1?.Category is null 
         ? x.Item2?.Category?.GetValue(x.Item2) 
         : x.Item1.Category.GetValue(x.Item1))
     .ThenBy(x => x.Item1?.Name is null 
          ? x.Item2?.Name?.GetValue(x.Item2) 
          : x.Item1.Name.GetValue(x.Item1))
     .ToList();

Jonathan Howell 20 Reputation points

2023-05-25T13:11:18.3566667+00:00

@Bruce (SqlWork.com) Thank you! That got it working.

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How does one sort a List of Tuples of two custom objects by a property in the first element, but if the first element is null, then use the second element's properties?

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