Get/set XML Schema and Content Types for SharePoint list directly in the content database

There is a charm about the forbidden that makes it unspeakably desirable.
— Mark Twain

Why would you do it?

Sometimes, despite all the warnings, you need to modify XML Schema and/or Content Types for SharePoint list directly in the content database. This could be caused by moving stuff, failed upgrade or removed SharePoint feature that resulted in broken lists.

In SharePoint 2007 and earlier that was fairly easy: you could just fire up SQL Management Studio, dig into the content database and fix it there: list’s Fields, that are part of list’s XML Schema are stored in tp_Fields column and Content Types are stored in the tp_ContentTypes column of the AllLists table in the content database.

So, what’s changed?

Starting with SharePoint 2010 most of the columns which contained plain XML (content type definitions, views, etc…) or BLOBs are now compressed in the database.

With luck and some googling around I’ve found that compressed objects format is documented in [MS-WSSFO3]: Windows SharePoint Services (WSS): File Operations Database Communications Version 3 Protocol. Those objects are called WSS Compressed Structures and consist of simple header followed by zlib comressed string.

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Writing stealth code in PowerShell

What happens in module, stays in module.

Most of my scripts are using Import-Component function to bulk-import dependencies (PS1 files with functions, modules, source code, .Net assemblies).

To import PS1 files with functions, they have to be dot-sourced and that provided me with some challenge: if PS1 is dot-sourced inside the function, it will be available only in that function’s scope. To overcome this, I could scope each contained function, alias, and variable as global (nasty!) or call Import-Component function itself using dot-sourcing (yes, you can dot-source more than just files).

For a while, dot-sourcing Import-Component seemed to work fine, until one day, I realized, that this effectively pollutes caller’s scope with all Import-Component‘s internal variables. Consider this example:

function DotSource-Me
{
    $MyString = 'Internal variable'
}

$MyString = 'External variable'

# Calling function as usual
DotSource-Me
Write-Host "Function was called, 'MyString' contains: $MyString"

# Dot-sourcing function
. DotSource-Me
Write-Host "Function was dot-sourced, 'MyString' contains: $MyString"

If we run this script, the output will be:

Function was called, 'MyString' contains: External variable
Function was dot-sourced, 'MyString' contains: Internal variable

As you can see, when the DotSource-Me function is called as usual, it’s internal variable is restricted to the function’s scope and doesn’t affect the caller’s scope. But when it’s dot-sourced, variable in the caller’s scope is overwritten.

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