Sharepoint via web service : checking if item exists in list

Question

Because Microsoft did not include a way to have unique constraints in sharepoint, this has to be done manually.

I am inserting items into a sharepoint list via a web service method.

How can I check if an existing list item already exists with the same field ID value?

I've learnt I should be using wsLists.getListitems web service method, but its not exactly "user friendly". MSDN documentation is again not really great at explaining what should be an easy thing to do.

Answer 1

Here's a procedure I wrote 2 years ago that pulls the ID of a document with a given filename... I think you could easily revise it to return true/false if a given ID exists in a list.

protected string GetDocumentID(Lists.Lists ls, string ListGUID, string FileName)
{
    string strDocumentID = "-1";

    string strViewGUID = "";
    string strRowLimit = "50000";

    XmlDocument xmlDoc = new XmlDocument();
    XmlNode query = xmlDoc.CreateNode(XmlNodeType.Element, "Query", "");
    XmlNode viewFields = xmlDoc.CreateNode(XmlNodeType.Element, "ViewFields", "");
    XmlNode queryOptions = xmlDoc.CreateNode(XmlNodeType.Element, "QueryOptions", "");

    query.InnerXml = "";
    viewFields.InnerXml = "";
    queryOptions.InnerXml = "<IncludeAttachmentUrls>TRUE</IncludeAttachmentUrls>";

    System.Xml.XmlNode nodeListItems = ls.GetListItems(ListGUID, strViewGUID, query, viewFields, strRowLimit, queryOptions, null);

    XmlDocument doc = new XmlDocument();
    doc.LoadXml(nodeListItems.InnerXml);
    XmlNamespaceManager nsmgr = new XmlNamespaceManager(doc.NameTable);
    nsmgr.AddNamespace("z", "#RowsetSchema");
    nsmgr.AddNamespace("rs", "urn:schemas-microsoft-com:rowset");

    foreach (XmlNode node in doc.SelectNodes("/rs:data/z:row", nsmgr))
    {
     if (node.Attributes["ows_LinkFilename"].Value == FileName)
     {
      strDocumentID = node.Attributes["ows_ID"].Value;
      break;
     }
    }

    return strDocumentID;
}

Here's the code that calls it...

Lists.Lists ls = new Lists.Lists();
ls.PreAuthenticate = true;
ls.Credentials = System.Net.CredentialCache.DefaultCredentials;
ls.Url = SharePointSiteURL + @"/_vti_bin/lists.asmx";

string DocID = GetDocumentID(ls, ListGUID, FileName);

Answer 2

private bool itemDoesntExist()
{
    XmlDocument doc = new XmlDocument();
    doc.LoadXml("<Document><Query><Where><Contains><FieldRef Name=\"ID\" /><Value Type=\"Text\">" + this.ID  + "</Value></Contains></Where></Query><ViewFields /><QueryOptions /></Document>");
    XmlNode listQuery = doc.SelectSingleNode("//Query");
    XmlNode listViewFields = doc.SelectSingleNode("//ViewFields");
    XmlNode listQueryOptions = doc.SelectSingleNode("//QueryOptions");
    XmlNode items = this.wsLists.GetListItems(this.ListName , string.Empty, listQuery, listViewFields, string.Empty, listQueryOptions, null);
    if (items.ChildNodes[1].Attributes["ItemCount"].Value == "0")
    {
        return true; 
    }
    else
    {
        return false; 
    }
}