Flatten a nested JSON with array and filter to CSV

Question

I got a question about How to use Powershell flatten a nested JSON and covert to CSV. Below is my JSON, which is a mail message log get from Office 365 with many users messages, I need to filter the columns, flatten and convert to CSV :

createdDateTime,
receivedDateTime,
from_name
from_adress
To_name_1
To_adress_2
To_name_2
To_adress_2
...

The "from" field has only one data. But the "toRecipients" is a array.

{
  ...
  "createdDateTime": "xxxx-xx-xx",
  "receivedDateTime": "xxxx-xx-xx",
  "isRead": true,
  "from": {
    "emailAddress": {
      "name": "John",
      "adress": "[email protected]"
    }
  },
  "toRecipients": [
    {
      "emailAddress": {
        "name": "Amy",
        "adress": "[email protected]"
      }
    },
    {
      "emailAddress": {
        "name": "Amy",
        "adress": "[email protected]"
      }
    }
  ]
}

Answer 1

Here is a complete runnable example. It will create a file "C:\test.csv".

There is no "automatic" way of flattening a nested object to a flat object. But you can manually create assign properties to a flat object.

First I parse the JSON text into a powershell object

$obj = @"
{
  "createdDateTime": "xxxx-xx-xx",
  "receivedDateTime": "xxxx-xx-xx",
  "isRead": true,
  "from": {
    "emailAddress": {
      "name": "John",
      "adress": "[email protected]"
    }
  },
  "toRecipients": [
    {
      "emailAddress": {
        "name": "Amy",
        "adress": "[email protected]"
      }
    },
    {
      "emailAddress": {
        "name": "Amy",
        "adress": "[email protected]"
      }
    }
  ]
}
"@ | ConvertFrom-Json

Now take the Powershell object (or list of objects, this will work even if you have many of these entries) and pipe it to ForEach-Object. Inside the loop map the different properties to a flat object.

$flattened = $obj | ForEach-Object {
    return [PSCustomObject]@{
        createdDateTime = $_.createdDateTime
        receivedDateTime = $_.receivedDateTime
        from_name = $_.from.emailAddress.name
        from_adress = $_.from.emailAddress.adress
        to_name_1 = $_.toRecipients[0].emailAddress.name
        to_adress_1 = $_.toRecipients[0].emailAddress.adress
        to_name_2 = $_.toRecipients[1].emailAddress.name
        to_adress_2 = $_.toRecipients[1].emailAddress.adress
    }
}

Now you can export the entire thing as a CSV

$flattened | Export-Csv C:\test.csv -Delimiter ";" -Encoding UTF8

This assumes that there will always be 2 toRecipients. It would be possible to dynamically add to_name_3, to_name_4, and so on if more are encountered, but that's quite a bit more complicated.