Selecting two things in linq one from inner json array and one from outer json array

Question

So I have a JSON object that looks like this

{
  "someOtherData": "notImportant",
  "outerlist": [
    {
      "somedata": 1504461600,
      "innerList": [
        {
          "data1": 801,
          "data2": "blah",
          "innerDataNeeded": "the inner list data needed"
        }
      ],
      "outerDataNeeded": "outer Data Needed"
    }
  ]
}

I was trying to write a linq query to return both the innerDataNeeded and the outerDataNeeded

So I wrote two to get both but I'm not sure how to connect them together and get the desired result with one query.

current code is like so

var listOfInnerData = from listItem in jsonObject["outerList"] from innerJsonList in listItem["innerList"] select (string) innerJsonList["innerDataNeeded"];
var listOfOuterData = from listItem in jsonObject["outerList"] select (string)listItem["outerDataNeeded"];

Convert your json to concrete classes, so you can work on it easier. json2csharp.com — L.B
– L.B, Commented Sep 3, 2017 at 18:30

dbc · Accepted Answer · 2017-09-04 07:38:50Z

You have a few options to extract the innerDataNeeded and outerDataNeeded, joined together in groups, using LINQ-to-JSON.

Firstly, you could use nested from statements to perform a SelectMany() on the inner list to generate a single, flat list of joined pairs:

var query = from outerItem in jsonObject.SelectTokens("outerlist[*]")
            let outerData = outerItem["outerDataNeeded"]
            from innerData in outerItem.SelectTokens("innerList[*].innerDataNeeded")
            select new { OuterData = (string)outerData, InnerData = (string)innerData };

var listOfData = query.ToList();

Resulting in

[
  {
    "OuterData": "outer Data Needed",
    "InnerData": "the inner list data needed"
  }
]

Secondly, if there is a possibility that the innerList array might be missing or empty and you still want to get the corresponding outer data values, you can sub in a default value using DefaultIfEmpty():

var query = from outerItem in jsonObject.SelectTokens("outerlist[*]")
            let outerData = outerItem["outerDataNeeded"]
            from innerData in outerItem.SelectTokens("innerList[*].innerDataNeeded").DefaultIfEmpty(JValue.CreateNull())
            select new { OuterData = (string)outerData, InnerData = (string)innerData };

var listOfData = query.ToList();

Finally, if you would prefer your list of results to be structured as outer an inner collections, you can use a nested LINQ query as follows:

var query = from outerItem in jsonObject.SelectTokens("outerlist[*]")
            select new 
            {
                OuterData = (string)outerItem["outerDataNeeded"], 
                InnerData = outerItem.SelectTokens("innerList[*].innerDataNeeded").Select(i => i.ToString()).ToArray() 
            };

var listOfData = query.ToList();

Which results in:

[
  {
    "OuterData": "outer Data Needed",
    "InnerData": [
      "the inner list data needed"
    ]
  }
]

Sample fiddle showing these three options.

Notes -

The method SelectTokens() enables selection of multiple tokens using JSONPath query syntax. In this syntax, the [*] operator is a wildcard that matches all array members. Using SelectTokens() avoids the need for nested from/select queries at each level of the JToken hierarchy.
If certain properties are missing, SelectTokens() will simply not enumerate over anything, whereas nested from/select will throw null reference exceptions unless null is checked for and skipped.
Pasting your JSON to http://json2csharp.com/ or using Paste JSON As Classes to generate concrete types for your JSON, then deserializing to those types and querying the result, is another option to consider.

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