Fix read-only properties on get operation WMI adapter

Author: Gijsreyn

adapters/wmi/Tests/wmi.tests.ps1

@@ -108,4 +108,16 @@ Describe 'WMI adapter resource tests' {
         $res.afterState.VariableValue | Should -Be 'update'
         $res.afterState.UserName | Should -Be ("{0}\{1}" -f $env:USERDOMAIN, $env:USERNAME)
     }
+
+    It 'Get works with read-only properties on Win32_ComputerSystem' -Skip:(!$IsWindows) {
+        $manufacturer = (Get-CimInstance -ClassName Win32_ComputerSystem).Manufacturer
+        $i = @{
+            Manufacturer = $manufacturer
+        } | ConvertTo-Json
+        
+        $r = dsc resource get -r root.cimv2/Win32_ComputerSystem -i $i
+        $LASTEXITCODE | Should -Be 0 
+        $res = $r | ConvertFrom-Json
+        $res.actualState.Manufacturer | Should -Not -BeNullOrEmpty
+    }
 }

adapters/wmi/wmiAdapter.psm1

@@ -186,22 +186,26 @@ function GetWmiInstance {
     $class = Get-CimClass -Namespace $wmi_namespace -ClassName $wmi_classname -ErrorAction Stop
 
     if ($DesiredState.properties) {
-        $properties = GetValidCimProperties -CimClass $class -ClassName $wmi_classname -Properties $DesiredState.properties -SkipReadOnly
+        # For GET operations, we should NOT skip read-only properties since we're just reading them
+        $properties = GetValidCimProperties -CimClass $class -ClassName $wmi_classname -Properties $DesiredState.properties
 
-        $query = BuildWmiQuery -ClassName $wmi_classname -Properties $properties -DesiredStateProperties $DesiredState.properties
+        # Only build query if we have properties to query
+        if ($properties -and $properties.Count -gt 0) {
+            $query = BuildWmiQuery -ClassName $wmi_classname -Properties $properties -DesiredStateProperties $DesiredState.properties
 
-        if ($query) {
-            "Query: $query" | Write-DscTrace -Operation Debug
-            $wmi_instances = Get-CimInstance -Namespace $wmi_namespace -Query $query -ErrorAction Ignore -ErrorVariable err
+            if ($query) {
+                "Query: $query" | Write-DscTrace -Operation Debug
+                $wmi_instances = Get-CimInstance -Namespace $wmi_namespace -Query $query -ErrorAction Ignore -ErrorVariable err
 
-            if ($null -eq $wmi_instances) {
-                "No WMI instances found using query '$query'. Retrying with key properties only." | Write-DscTrace -Operation Debug
-                $keyQuery = BuildWmiQuery -ClassName $wmi_classname -Properties $properties -DesiredStateProperties $DesiredState.properties -KeyPropertiesOnly
+                if ($null -eq $wmi_instances) {
+                    "No WMI instances found using query '$query'. Retrying with key properties only." | Write-DscTrace -Operation Debug
+                    $keyQuery = BuildWmiQuery -ClassName $wmi_classname -Properties $properties -DesiredStateProperties $DesiredState.properties -KeyPropertiesOnly
 
-                if ($keyQuery) {
-                    $wmi_instances = Get-CimInstance -Namespace $wmi_namespace -Query $keyQuery -ErrorAction Ignore -ErrorVariable err
-                    if ($null -eq $wmi_instances) {
-                        "No WMI instances found using key properties query '$keyQuery'." | Write-DscTrace -Operation Debug
+                    if ($keyQuery) {
+                        $wmi_instances = Get-CimInstance -Namespace $wmi_namespace -Query $keyQuery -ErrorAction Ignore -ErrorVariable err
+                        if ($null -eq $wmi_instances) {
+                            "No WMI instances found using key properties query '$keyQuery'." | Write-DscTrace -Operation Debug
+                        }
                     }
                 }
             }