How can I convert a hastable to a json string in powershell?

Question

I'm trying to convert a hashtable to a json object for use in a web service with powershell 2.0.

$testhash = @{
    Name = 'John Doe'
    Age = 10
    Amount = 10.1
    MixedItems = (1,2,3,"a")
    NestedHash = @{
        nestedkey = "nextedvalue"
    }
}

function toJson($obj){

    $ms = New-Object IO.MemoryStream
    $type = $obj.getType()
    [Type[]]$types = ($obj | select -expand PsTypeNames |  Select -unique) + [type]'System.Management.Automation.PSObject'
    $js = New-Object System.Runtime.Serialization.Json.DataContractJsonSerializer $type, $types, ([int]::MaxValue), $false, $null, $false
    $js.writeObject($ms, $obj) | out-null
    $utf8.GetString( $ms.ToArray(), 0, $ms.Length )
    $ms.Dispose() | out-null
}

toJson $testhash
'[{"Key":"Name","Value":"John Doe"},{"Key":"Age","Value":10},{"Key":"Amount","Value":10.1},{"Key":"NestedHash","Value":[{"__type":"KeyValuePairOfanyTypeanyType:#System.Collections.Generic","key":"nestedkey","value":"nextedvalue"}]},{"Key":"MixedItems","Value":[1,2,3,"a"]}]'

I'm using DataContractJsonSerializer constructor in a way that should suppress type information but it's obviously not. I'm also amused by it's extracting key and value pairs but I'd like to have it not do that either. What am I doing wrong?

Answer 1

Ok, so manojlds answered for v2 so I'll just throw up the v3 equivalent here:

PS> @{name="oisin"; age=37} | convertto-json
{
    "age":  37,
    "name":  "oisin"
}

Quite a bit cleaner, right?

PowerShell 3.0 CTP2: http://www.microsoft.com/download/en/details.aspx?id=27548

Answer 2

I adapted the script from here as below:

$testhash = @{
    Name = 'John Doe'
    Age = 10
    Amount = 10.1
    MixedItems = (1,2,3,"a")
    NestedHash = @{
        nestedkey = "nextedvalue"
    }
}

function Read-Stream {
PARAM(
   [Parameter(Position=0,ValueFromPipeline=$true)]$Stream
)
process {
   $bytes = $Stream.ToArray()
   [System.Text.Encoding]::UTF8.GetString($bytes,0,$bytes.Length)
}}

function New-Json {
[CmdletBinding()]
param([Parameter(ValueFromPipeline=$true)][HashTable]$InputObject) 
begin { 
   $ser = @{}
   $jsona = @()
}
process {
   $jsoni = 
   foreach($input in $InputObject.GetEnumerator() | Where { $_.Value } ) {
      if($input.Value -is [Hashtable]) {
         '"'+$input.Key+'": ' + (New-JSon $input.Value)
      } else {
         $type = $input.Value.GetType()
         if(!$Ser.ContainsKey($Type)) {
            $Ser.($Type) = New-Object System.Runtime.Serialization.Json.DataContractJsonSerializer $type
         }
         $stream = New-Object System.IO.MemoryStream
         $Ser.($Type).WriteObject( $stream, $Input.Value )
         '"'+$input.Key+'": ' + (Read-Stream $stream)
      }
   }

   $jsona += "{`n" +($jsoni -join ",`n")+ "`n}"
}
end { 
   if($jsona.Count -gt 1) {
      "[$($jsona -join ",`n")]" 
   } else {
      $jsona
   }
}}

$testHash | New-Json