CAML "In" Operator Equivalent For SharePoint Services 3 (SharePoint 2007)

Question

Today I came across the need to write a CAML query that uses WHERE [Field] IN [Values]. I wanted to query a List where the list item's Title was contained by a collection of strings. After receiving several errors running my query, I realized the In operator was new to SharePoint 2010 but I'm still in SharePoint 2007. As a result, the only option is to use multiple Or operators. Additionally an Or operator can only operate on 2 values at a time so this requires nested Or operators. How can you build such a query? See my solution below.

Answer 1

I stumbled around a couple approaches before coming to this solution. I'm not sure of its scalability but it suits my needs so I thought I would share it. This recursive method should return the equivalent of

WHERE Title IN ([Title1], [Title2],...[TitleN]) 

for a List of 1-N string titles.

private string _camlTitleEq = "<Eq>" +
                                 "<FieldRef Name=\"Title\" />" +
                                 "<Value Type=\"Text\">{0}</Value>" +
                              "</Eq>";

private XElement BuildOrClause(List<string> listItemTitles, int index)
{
    //If we've reached the last item in the list, return only an Eq clause
    if (index == listItemTitles.Count - 1)
        return XElement.Parse(String.Format(_camlTitleEq, listItemTitles[index]));
    else
    {
        //If there are more items in the list, create a new nested Or, where
        //the first value is an Eq clause and the second is the result of BuildOrClause
        XElement orClause = new XElement("Or");
        orClause.Add(XElement.Parse(String.Format(_camlTitleEq, listItemTitles[index])));
        orClause.Add(BuildOrClause(listItemTitles, index + 1));
        return orClause;
    }
}

And you could use it like so:

SPQuery query = new SPQuery();
string titleIn = BuildOrClause(listItemTitles, 0).ToString(SaveOptions.DisableFormatting);

query.Query = "<Where>" +
                  titleIn +
              "</Where>";

I hope this helps someone still working in SP 2007. Constructive feedback is welcome! If you're in SharePoint 2010, use the already built in In Operator.