How to modify Author field of ListItem

Question

I am building a migration tool that is migrating items from an XML schema to SharePoint list fields. Everything is working fine except when it comes to the migration of Created By fields. I need to use the client object model to do this.

So far this is what I have:

using (ClientContext ctx = new ClientContext(url))
{
      List lst = ctx.Web.Lists.GetByTitle("list name");
      Field field = lst.Fields.GetByTitle("Created By");
      field.ReadOnlyField = false; //Allow the field to be modified

      //...Get all list items and store in ListItemCollection named 'col'
      foreach (ListItem item in col)
      {
           item["Author"] = xmlNodeValue; //Take the User form the xml schema and insert into sharepoint's created by field
           item.Update();
           ctx.Credentials = creds;
           ctx.ExecuteQuery();
      }
}

The exception thrown when executing against the server:

Invalid data has been used to update the list item. The field you are trying to update may be read only.

I realize that I probably can't store a string of xmlNodeValue in that field, so how can I achieve this?

Also please keep in mind that the user name pulled from xmlNodeValue may not exist as a claims user.

Answer 1

In order to modify/update the Author field using the client object model, you need to make sure to

• Load the Source Item
• Load the User Object with Source Context
• Ensure the User Object in the Destination Context
• Insert the User Object in the Destination Item
• Update the Destination Item

Please find below the pseudo code.

sourceCtx.Load(sourceItem);
sourceCtx.ExecuteQuery();

FieldUserValue val = sourceItem["Author"] as FieldUserValue;

User user = sourceCtx.Web.EnsureUser(val.LookupValue);
sourceCtx.Load(user);
sourceCtx.ExecuteQuery();

newDestItem["Author"] = destinationCtx.Web.EnsureUser(user.LoginName);
newDestItem.Update();

Please let me know if you have any further queries.

Thanks, Dinesh

Answer 2

Update Author and Editor at the same time for the first version only or Final file without versions.

if (firstVersion || noVersion)
{
authorUserName = ((FieldUserValue)liSource["Author"]).Email;
User author = contextDest.Web.EnsureUser(authorUserName);

if (author != null)
{
    contextDest.Load(liDest, l => l["Author"], l => l["Editor"], l => l["Created"]);
    contextDest.ExecuteQuery();

    // IMPORTANT: Must be same name to get author updated
    liDest["Editor"] = author;
    liDest["Author"] = author;
    liDest["Created"] = liSource["Created"];
    liDest["Modified"] = liSource["Modified"];
    liDest.UpdateOverwriteVersion();
    contextDest.ExecuteQuery();
}
}

Answer 3

Use Web.EnsureUser method to get the User object and then use that to update the Author https://msdn.microsoft.com/EN-US/library/microsoft.sharepoint.client.web.ensureuser.aspx