Automatically add tag to uploaded document in sharepoint - file-upload

Question

My environment is sharepoint 2010 and vs 2010.
I already have an OOTB document library that I am using and I wanted to know how I can add a tag or keyword to a METADATA column.
I am using the same document library in all subsites and so would like to tag the uploaded document with the name of the current site (ie if it's being used in a subsite, that subsite's name would be the tag).
Would I need to build a custom document library or some sort of add-on webpart that attaches to the existing document library?
If you could provide some code samples if any that would be appreciated.
thanks,
KS

Answer 1

If you are starting from scratch you can create a custom content type based on the build in content type Document (a child content type of Document). Add a custom field to your content type. For more information regarding creating content types look here: http://msdn.microsoft.com/en-us/library/gg295290.aspx
A content type can also have a custom event receiver for ItemAdding, ItemUpdated etc. Look at the xml below:
<Elements xmlns="http://schemas.microsoft.com/sharepoint/">
<ContentType ID="0x010100xxxxxx"
Name="MyContentType"
Group="My custom group" Version="0" Inherits="True" Overwrite="TRUE" >
<FieldRefs>
<FieldRef ID="{AC8A823D-EB2F-4D4D-8BF0-14CACA509539}" Name="myMetadataField" Required="FALSE" />
</FieldRefs>
<XmlDocuments>
<XmlDocument NamespaceURI="http://schemas.microsoft.com/sharepoint/events">
<spe:Receivers xmlns:spe="http://schemas.microsoft.com/sharepoint/events">
<Receiver>
<SequenceNumber>1010</SequenceNumber>
<Name>HandoverOffshore_ItemAddedReceiver</Name>
<Type>ItemAdded</Type>
<Assembly>MyAssembly, Version=1.0.0.0, Culture=neutral, PublicKeyToken=79315a88caec227a</Assembly>
<Class>MyAssembly.CustomEventReceivers</Class>
</Receiver>
</spe:Receivers>
</XmlDocument>
</XmlDocuments>
</ContentType>
</Elements>
Then you'll have to create the event receiver class witch handles the custom event:
public class HandoverOffshoreEventReceivers : SPItemEventReceiver
{
public override void ItemAdded(SPItemEventProperties properties)
{
// your code for updating metadata field here...
}
}
Then you deploy this to your site collection and add this content type to all your libraries. Also set this as the default content type in all libraries.
If you are creating many libraries you should consider to create a custom library definition based on this content type.
If you want this custom event fired for existing documents you'll have to change their content type to the new one you created here.
Note that document library content types are child content types of the site collection content types.