Powershell nested JSON to csv conversion

Question

I have a rather peculiar nested JSON where in some instances a key - value pair occurs as normal, but in others the type of the key appears in a further nesting.

{"metadata":{"systemId":"da1895","legalEntity":"A0"},"recordContent":{"positionDate":"2019-04-08 00:00:00.0","account":{"string":"G32"},"seg":{"string":"S"},"strike":{"double":4.4}}}
{"metadata":{"systemId":"45364d","legalEntity":"5G"},"recordContent":{"positionDate":"2019-04-08 00:00:00.0","account":{"string":"G81"},"seg":{"string":"S"},"strike":{"double":5.0}}}

In the example you can see metadata's fields are straightforward key-value pairs, but underneath recordContent, we have positionDate which is a straightforward key-value but "account":{"string":"G32"} and "strike":{"double":4.4} are not.

I'd like to ditch the type information and arrive at a CSV structure as follows:

systemId, legalEntity, positionDate,         account,seg,strike
da1895,   A0,          2019-04-08 00:00:00.0,G32,    S,  4.4
4536d,    5G,          2019-04-08 00:00:00.0,G81,    S,  5.0

Any ideas on how to convert such a structure to CSV using Powershell?

Here's what I tried:

$TemplateParametersFile = "c:\data\output.json"
$JsonParameters = Get-Content $TemplateParametersFile | ConvertFrom-Json

$metadatafields = $JsonParameters.metadata[0].PSObject.Properties.Name
$recordcontentfields = $JsonParameters.recordContent[0].PsObject.Properties.Name

$oData = New-Object PSObject

$metadatafields |
ForEach {
    Add-Member -InputObject $oData -NotePropertyName ($_) -NotePropertyValue $JsonParameters.metadata.($_)
}

$recordcontentfields |
ForEach {
    Add-Member -InputObject $oData -NotePropertyName ($_) -NotePropertyValue $JsonParameters.recordContent.($_)
}

This gave me:

$oData

systemId     : {da1895, 45364d}
legalEntity  : {A0, 5G}
positionDate : {2019-04-08 00:00:00.0, 2019-04-08 00:00:00.0}
account      : {@{string=G32}, @{string=G81}}
seg          : {@{string=S}, @{string=S}}
strike       : {@{double=4.4}, @{double=5.0}}

I'm a bit stuck now and the above doesn't convert to csv.

Note that other than metadata and recordContent, I've not hardcoded any fieldnames and I'd like to maintain that flexibility in case the JSON structure changes.

Thanks

Answer 1

I suggest collecting the property-name-value pairs iteratively in an ordered hashtable ([ordered] @{}), which can then be cast to [pscustomobject] to convert it to a custom object.

No property names are hard-coded in the following solution, but the object-graph structure is assumed to follow the pattern in your sample JSON, which is limited to one level of nesting - if you need to process arbitrarily nested objects, this answer may be a starting point.

Reflection (discovery of the property names and values) is performed via the intrinsic .psobject property that PowerShell makes available on all objects.

# Parse sample JSON into an array of [pscustomobject] graphs.
$fromJson = ConvertFrom-Json @'
[
  {"metadata":{"systemId":"da1895","legalEntity":"A0"},"recordContent":{"positionDate":"2019-04-08 00:00:00.0","account":{"string":"G32"},"seg":{"string":"S"},"strike":{"double":4.4}}}
  ,
  {"metadata":{"systemId":"45364d","legalEntity":"5G"},"recordContent":{"positionDate":"2019-04-08 00:00:00.0","account":{"string":"G81"},"seg":{"string":"S"},"strike":{"double":5.0}}}
]
'@

# Initialize an aux. ordered hashtable to collect the property-name-value
# pairs in.
$oht = [ordered] @{}

$fromJson | ForEach-Object {
    $oht.Clear()
    # Loop over top-level properties.
    foreach ($topLevelProp in $_.psobject.Properties) {
      # Loop over second-level properties.
      foreach ($prop in $topLevelProp.Value.psobject.Properties) {
        if ($prop.Value -is [System.Management.Automation.PSCustomObject]) {
          # A nested value: Use the value of the (presumed to be one-and-only)
          #                 property of the object stored in the value.
          $oht[$prop.Name] = $prop.Value.psobject.Properties.Value
        }
        else {
          # A non-nested value: use as-is.
          $oht[$prop.Name] = $prop.Value
        }
      }
    }
    # Construct and output a [pscustomobject] from the aux. ordered hashtble.
    [pscustomobject] $oht
  } |
      ConvertTo-Csv  # Replace this with Export-Csv to export to a file.

The above yields:

"systemId","legalEntity","positionDate","account","seg","strike"
"da1895","A0","2019-04-08 00:00:00.0","G32","S","4.4"
"45364d","5G","2019-04-08 00:00:00.0","G81","S","5"