Powershell replace values in target.json with values from source.json

Question

I have a big target json file (parameters_general.json) where all common settings for a deployment are set. For each tier I have another json file (ex: parameters_dev.json, parameters_test.json, ....) Settings set in one needs tobe added to the general.json, or overwrite it when already in general.

ex: parameters_general.json

{ 
  "general": {
    "db_Policy": {
    "type": "Periodic",
    "databaseAccountOfferType": "Standard",
    "periodicModeProperties": {
      "backupIntervalInMinutes": 240,
      "backupRetentionIntervalInHours": 8,
      "backupStorageRedundancy": "Local"
    }      
  },
  "databases": [
    { 
      "name": "CtrlWps", 
      "Containers": [
        {
          "name": "ControllerAuthentication",
          "partitionKey": "id"
        }
      ],
      "ContainersTTL": []
    },
    { 
      "name": "CpoOcpi",
      "Containers": [
        {
          "name": "Cpos",
          "partitionKey": "cpoId"
        },          
        {
          "name": "OcpiCdrLastRecoveries",
          "partitionKey": "id"
        },
        {
          "name": "Routes",
          "partitionKey": "ocpiCpoId"
        }
      ],
      "ContainersTTL": [
        {
          "name": "OcpiCdrs",
          "partitionKey": "pk",
          "ttl": 172800
        },
        
        {
          "name": "OcppTransactionIds",
          "partitionKey": "pk",
          "ttl": 172800
        },
        {
          "name": "Sessions",
          "partitionKey": "pk",
          "ttl": 172800
        }     
      ]
    }
  ],
  "system_engineers": [
  ],
 }
}

If I want to updatethis with.

ex: parameters_test.json

{ 
  "general": {
    "system_engineers": [
      {
        "name": "hans",
        "AppPrincipalId": "<id>",
        "permissions": [
          "get",
          "list"
        ]
      },
      {
        "name": "John do",
        "AppPrincipalId": "<pid>",
        "permissions": [
          "all"
        ]
      }
    ]
  }
}

This works, the users are added to the empty "sytem_engineers" node in the parameters_general.json.

However, If I just want to change a setting on a lower node example:

ex: parameters_dev.json

{
  "general": {
    "databases": [
        { 
          "name": "CtrlWps", 
          "Containers": [
            {
              "name": "ControllerAuthentication",
              "partitionKey": "pk"
            }
          ]
        }
    ]
  }
}

for replacing the partitionKey in one of the databases it replaces the whole "databases" part so I lose all other database configurations in the target.

The code I use is the following.

function ExtendJSON($base, $ext)
{
    $propNames = $($ext | Get-Member -MemberType *Property).Name
    foreach ($propName in $propNames) {
        if ($base.PSObject.Properties.Match($propName).Count) {
            if ($base.$propName.GetType().Name -eq "PSCustomObject")
            {
                $base.$propName = ExtendJSON $base.$propName $ext.$propName
            }
            else
            {
                $base.$propName = $ext.$propName
            }
        }
        else
        {
            $base | Add-Member -MemberType NoteProperty -Name $propName -Value $ext.$propName
        }
    }
    return $base
}

$tier = 'dev'  
$parametersJsonGeneral = Get-Content -Path "./parameters/parameters_general.json" | ConvertFrom-Json
#Write-Output "#####################"
$parametersJsonTier = Get-Content -Path "./parameters/parameters_$($tier).json" | ConvertFrom-Json   # overwrites existing values in $parametersJsonGeneral
ExtendJSON $parametersJsonGeneral $parametersJsonTier 

Is there a way to loop over the settings from the lowest level up to the higher, and replace only these?

The proposed answer does only work one 1st level THIS WORKS

function merger ($target, $source) {
    $source.psobject.Properties | ForEach-Object {
        if ($_.TypeNameOfValue -eq 'System.Management.Automation.PSCustomObject' -and $target."$($_.Name)" ) {
            merger $target."$($_.Name)" $_.Value
        }
        else {
            $target | Add-Member -MemberType $_.MemberType -Name $_.Name -Value $_.Value -Force
        }
    }
}


$Json1 ='{
    "a": {
      "b":"asda"
    },
    "c": "asdasd"
  }
  ' | ConvertFrom-Json
  
  $Json2 = '{
    "a": {
      "b":"d"
    }
  }
  ' | ConvertFrom-Json

merger $Json1 $Json2

However with this I loose data in $Json1

$Json1 ='{
    "a": {
      "b": [
          { 
            "name": "admin",
            "appconfig": {
                "test1": true,
                "test2": false
            }
          }
        ]
    },
    "c": "asdasd"
  }
  ' | ConvertFrom-Json
  
  $Json2 = '{
    "a": {
        "b": [
            { 
              "name": "admin",
              "appconfig": {
                  "test1": false
              }
            }
          ]
    }
  }
  ' | ConvertFrom-Json

merger $Json1 $Json2

{
  "a": {
    "b": [
      {
        "name": "admin",
        "appconfig": {
          "test1": false
        }
      }
    ]
  },
  "c": "asdasd"
}

test2 is gone!

Answer 1

I don't have enough rep to post general comments yet, so I'll have to post it as an answer:

I tested the code in this answer to another question, and it did what you asked. The advantage of this answer is that it doesn't depend on importing a separate module.

There's another answer in the same question that provides link to a more general module that provides for different types of merges (Left Join, Inner Join, etc.) here, which links to here. However, one commenter said that it didn't work with powershell 7.0.