Error using SPWebConfigModification to update web.config

Question

I am trying to update web.config using SPWebConfigModification and I am getting the following error:

Exception calling "ApplyWebConfigModifications" with "0" argument(s): "Object reference not set to an instance of an
object."
At line:11 char:1
+ $app.Parent.ApplyWebConfigModifications();
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : NullReferenceException

This is my powershell script:

$app = Get-SPWebApplication http://test:8000/
$mod = New-Object Microsoft.SharePoint.Administration.SPWebConfigModification
$mod.Path = “configuration/SharePoint/WebPartLimits”
$mod.Name = “MaxZoneParts”
$mod.Value = “100”
$mod.Sequence = 0
$mod.Owner = “webpartmod”
$mod.Type = 1    
$app.WebConfigModifications.Add($mod)
$app.update()
$app.Parent.ApplyWebConfigModifications();

I have verified that $app and $mod are not null. What else could be causing this error?

Answer 1

The error is stating that you can’t call ApplyWebConfigModifications() on $app.Parent. In this case, it is the Parent property of $app that is null.

SPWebApplication’s Parent property is of type SPPersistedObject which doesn’t have an ApplyWebConfigModifications method and is most likely null in this case as SPWebApplications aren’t hierarchical/nested.

ApplyWebConfigModifications() does exist on the SPWebService property of the SPWebApplication.

The line should read: $app.WebService.ApplyWebConfigModifications();