Programmatically finding and using a person using Client Side Object Model

I have a custom table and one of the fields is a Person column column called Answered By. In the SharePoint UI the person can type in the persons username (same as email if you are using SharePoint Online) or use the Person Picker to find the person. In the code below we want to find them by username.

using (ClientContext clientContext = ClaimClientContext.GetAuthenticatedContext("https://myco.sharepoint.com/site1/site2"))
{
    var user = clientContext.Web.EnsureUser("me@myco.com");
}

Once you have the person you can then use it when setting the value for that field programmatically. In this example I am creating a new list item and setting the Answered By field using the person object that I find using the EnsureUser() method.

using (ClientContext clientContext = ClaimClientContext.GetAuthenticatedContext("https://myco.sharepoint.com/site1/site2"))
    {
        var destList = clientContext.Web.Lists.GetByTitle("FAQs");
        var itemCreateInfo = new ListItemCreationInformation();
        var newItem = destList.AddItem(itemCreateInfo);
        newItem["Title"] = "Some title here";
        var user = clientContext.Web.EnsureUser(brent.vermilion@nxp.com);
        newItem["Answered_x0020_By"] = user;
        newItem.Update();
        // actually create the records in the destination list
        clientContext.ExecuteQuery();
    }

Take note, I could have also put the integer instead of the user object, but I think this actually saves a trip to the database and is cleaner. I also found it interesting that spaces in column names in SharePoint have the space replaced by the space with a notation that uses the hex value for space (20).

To learn more about CRUD operation and other useful topics see this intro.