Select List of another List by separating delimiter in Linq

Question

I'm trying to select a list which is having another list itself. But the thing is I've needed to use some delimiter to separate my two list

My List is

{
    "Order": {
        "Items": [
            {
                "Details": [
                    {
                        "Product": "XXX",
                        "Category": "YYY"
                    },
                    {
                        "Product": "ZZZ",
                        "Category": "YYY"
                    }
                ]
            },
            {
                "Details": [
                    {
                        "Product": "AAA",
                        "Category": "BBB"
                    }
                ]
            }
        ]
    }
}

My Final output should be like

XXX|YYYY^ZZZ|YYY^AAA|BBB

Currently, I'm using the solution as like below.

 StringBuilder output= new StringBuilder();
 string delimiter = "";
 foreach (var items in order.Items) {
      output.Append(delimiter);
      output.Append(string.Join("^",items.Details.Select(l => l.Product+"|"+l.Category)));
      delimiter = "^";
 }    

But this is not the best option. Please help to find the good one.

Answer 1

You can use a single string.Join with LINQ's SelectMany:

string result = string.Join("^", order.Items.SelectMany(
          item => item.Details.Select(detail => $"{detail.Product}|{detail.Category}")));

This goes through all Details of all Items and creates your "Product|Category" strings. Then these strings are all joined with "^" as delimiter.

---

I don't know your criteria for "good". If you find this readable and think your co-workers will also understand it, I guess it's good. There maybe more efficient ways (in terms of consumed time), but I think this will only be a real matter if you have billions of Details or need to execute it twice per millisecond.