Powershell JSON Manipulation - json

Question

$parent = #"
{
"Property1": "Property1Value",
"Description": "Generic Description",
"SubProperties": {
"SubSubTemplateProps": {
SubSubSubTemplateProps1 : "SubSubSubTemplateProps1",
SubSubSubTemplateProps2 : {
SubSubSubSubTemplateProps1 : [
{
"Key": "Name",
"Value": "Temp"
},
{
"Key": "SupSubSubProp2",
"Value": "Supprop2value"
}
]
}
}
}
}
"# | ConvertFrom-Json
$templateobj = $parent.SubProperties.SubSubTemplateProps
$parent.SubProperties.psobject.Properties.Remove("SubSubTemplateProps")
for($j = 0; $j -lt 3; $j++)
{
$i = "{0:D2}" -f ($j+1)
$letters = #("a","b","c")
foreach($letter in $letters)
{
$newobject = $templateobj
($newobject.SubSubSubTemplateProps2.SubSubSubSubTemplateProps1 | ? {$_.key -eq "Name"}).Value = "NewValue$letter$i"
$parent.SubProperties | Add-Member -MemberType NoteProperty -Name "SubSubProp$letter$i" -Value $newobject
}
}
$parent |convertto-json -Depth 100
Im expecting output like this:
{
"Property1": "Property1Value",
"Description": "Generic Description",
"SubProperties": {
"SubSubPropa01": {
"SubSubSubTemplateProps1": "SubSubSubTemplateProps1",
"SubSubSubTemplateProps2": {
"SubSubSubSubTemplateProps1": [
{
"Key": "Name",
"Value": "NewValuea01"
},
{
"Key": "SupSubSubProp2",
"Value": "Supprop2value"
}
]
}
},
"SubSubPropb01": {
"SubSubSubTemplateProps1": "SubSubSubTemplateProps1",
"SubSubSubTemplateProps2": {
"SubSubSubSubTemplateProps1": [
{
"Key": "Name",
"Value": "NewValueb01"
},
{
"Key": "SupSubSubProp2",
"Value": "Supprop2value"
}
]
}
},
"SubSubPropa02": {
"SubSubSubTemplateProps1": "SubSubSubTemplateProps1",
"SubSubSubTemplateProps2": {
"SubSubSubSubTemplateProps1": [
{
"Key": "Name",
"Value": "NewValuea02"
},
{
"Key": "SupSubSubProp2",
"Value": "Supprop2value"
}
]
}
},
"SubSubPropb02": {
"SubSubSubTemplateProps1": "SubSubSubTemplateProps1",
"SubSubSubTemplateProps2": {
"SubSubSubSubTemplateProps1": [
{
"Key": "Name",
"Value": "NewValueb02"
},
{
"Key": "SupSubSubProp2",
"Value": "Supprop2value"
}
]
}
}
}
}
But I get output like this where all of the noteproperties of the parent are updated instead of just the noteproperty I added. WHAT?!
{
"Property1": "Property1Value",
"Description": "Generic Description",
"SubProperties": {
"SubSubPropa01": {
"SubSubSubTemplateProps1": "SubSubSubTemplateProps1",
"SubSubSubTemplateProps2": {
"SubSubSubSubTemplateProps1": [
{
"Key": "Name",
"Value": "NewValueb02"
},
{
"Key": "SupSubSubProp2",
"Value": "Supprop2value"
}
]
}
},
"SubSubPropb01": {
"SubSubSubTemplateProps1": "SubSubSubTemplateProps1",
"SubSubSubTemplateProps2": {
"SubSubSubSubTemplateProps1": [
{
"Key": "Name",
"Value": "NewValueb02"
},
{
"Key": "SupSubSubProp2",
"Value": "Supprop2value"
}
]
}
},
"SubSubPropa02": {
"SubSubSubTemplateProps1": "SubSubSubTemplateProps1",
"SubSubSubTemplateProps2": {
"SubSubSubSubTemplateProps1": [
{
"Key": "Name",
"Value": "NewValueb02"
},
{
"Key": "SupSubSubProp2",
"Value": "Supprop2value"
}
]
}
},
"SubSubPropb02": {
"SubSubSubTemplateProps1": "SubSubSubTemplateProps1",
"SubSubSubTemplateProps2": {
"SubSubSubSubTemplateProps1": [
{
"Key": "Name",
"Value": "NewValueb02"
},
{
"Key": "SupSubSubProp2",
"Value": "Supprop2value"
}
]
}
}
}
}
Can someone suggest how to copy a node and replace a sub value then add it back to the parent without it overwriting all other child nodes? Not sure why this is happening.

Answer 1

The fundamental problem, as explained in the comments and in more detail in this related answer is:
[pscustomobject] instances, such as returned by ConvertFrom-Json are instances of a .NET reference type, which means that $newobject = $templateobj doesn't create a copy of the object stored in $templateobj in $newobject, it creates a copy of the reference to object $templateobj, so that $templateobj and $newobject end up pointing to the very same object. Only instances of .NET value types are themselves copied with simple assignments - see this answer for background information.
Therefore, you ended up repeatedly modifying the very same object instead of independent copies of it.
While $templateobj.psobject.Copy() is a convenient method to create a shallow clone (copy) of a [pscustomobject] instance, it isn't sufficient in your case, because your instances also contain reference-type instances among the object's property values, which then again get copies as references.
In other words: your template object is a [pscustomobject] graph (nested), so it requires deep-cloning, for which there is no built-in method.
Note: If you know the structure of the template object ahead of time, there are simpler and more efficient solutions:
Use a literal [pscustomobject] object definition inside your loop, which creates a new instance every time - see the related answer.
Construct your template as an ordered hashtable ([ordered] #{ ... }), and cast it to [pscustomobject] every time you need a new copy inside the loop - see this answer
Define a custom class and instantiate it in every loop iteration - see this answer.
If you do need deep-cloning of [pscustomobject] graphs, use helper function Copy-PSCustomObject, defined further below, with the -Deep switch:
$newobject = Copy-PSCustomObject -Deep $templateobj
Helper function Copy-PSCustomObject:
Note: This is not a generic deep-cloning function that works with objects of any type (which would be impossible to implement), but it should work with [pscustomobject] graphs such as returned by ConvertFrom-Json, which limits their composition to:
Primitive JSON types that map onto primitive .NET types and [string], all of which either are .NET value types or, in the case of [string] act like them.
Nested [pscustomobject] instances with the same composition.
Arrays of either.
function Copy-PSCustomObject {
[CmdletBinding()]
param(
[Parameter(Mandatory, ValueFromPipeline)]
[PSCustomObject] $InputObject,
[switch] $Deep
)
begin {
if ($Deep) {
# Helper script block (anonymous function) for walking the object graph
$sb = {
param($original)
$copy = $original.psobject.Copy()
foreach ($prop in $copy.psobject.Properties) {
if ($prop.Value -is [System.Collections.IEnumerable]) { # Presumed array
$prop.Value = #($prop.Value) # Clone array
foreach ($i in 0..($prop.Value.Count-1)) {
$prop.Value[$i] = & $sb $prop.Value[$i] # Recurse
}
}
elseif ($prop.Value -is [System.Management.Automation.PSCustomObject]) {
$prop.Value = & $sb $prop.Value # Recurse
}
# Otherwise: assume it is a value type or string and needs no cloning.
}
# Output the deep-cloned object
$copy
}
}
}
process {
if ($Deep) {
& $sb $InputObject
}
else {
# Shallow copy.
$InputObject.psobject.Copy()
}
}
}