SharePoint UserData and the ;# Syntax in returned data

Question

Can a SharePoint expert explain to me the ;# in data returned by the GetListItems() call to the Lists web service?

I think I understand what they are doing here. The ;# is almost like a syntax for making a comment... or better yet, including the actual data (string) and not just the ID. This way you can use either, but they are nicely paired together in the same column.

Am I way off base? I just can't figure out the slighly different use. For example

I have a list with:    
ows_Author  
658;#Tyndall, Bruno    
*in this case the 658 seems to be an ID for me in a users table somewhere*

ows_CreatedDate (note: a custom field. not ows_Created)    
571;#2009-08-31 23:41:58    
*in this case the 571 seems to be an ID of the row I'm already in. Why the repetition?*   

Can anyone out there shed some light on this aspect of SharePoint?

Answer 1

The string ;# is used as a delimiter by SharePoint's lookup fields, including user fields. When working with the object model, you can use SPFieldLookupValue and SPFieldUserValue to convert the delimited string into a strongly-typed object. When working with the web services, however, I believe you'll need to parse the string yourself.

You are correct that the first part is an integer ID: ID in the site user list, or ID of the corresponding item in the lookup list. The second part is the user name or value of the lookup column.

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Nicolas correctly notes that this delimiter is also used for other composite field values, including...

• SPFieldLookupValueCollection
• SPFieldMultiColumnValue
• SPFieldMultiChoiceValue
• SPFieldUserValueCollection

Answer 2

The SPFieldUser inherits from the SPFieldLookup which uses the ;# notation. You can easily parse the value by creating a new instance of the SPFieldLookupValue class:

string rawValue = "1;#value";
SPFieldLookupValue lookupValue = new SPFieldLookupValue(rawValue);
string value = lookupValue.LookupValue; // returns value