Delete column from list using Client Object Model

Question

Developing for SharePoint Online, I've created a Contact List programmatically in my app. I now want to delete some of the columns that were added to the list. So I have the following code:

var lastName = list.Fields.GetByInternalNameOrTitle("Last Name");
if (lastName != null) {
    lastName.DeleteObject();
}

. . .

clientContext.ExecuteQuery();

But this does not delete the column. In fact, when contained in a try {...} catch {...}, I get the following exception message:

Operation is not valid due to the current state of the object.

Looking at the various properties on the Field object, I can see the CanBeDeleted property is false, so I can only assume that this is the cause for the above message. But this property is also read-only, so I can't force it to be deleted.

So my question is, how would I go about deleting these columns? When I add a Contact List to my app using Visual Studio, I'm able to delete these columns through the tooling, so I want to do the same in code.

Any help would be greatly appreciated.

Answer 1

You cannot delete a field with CanBeDeleted property as false as it indicates whether the field can be deleted or not.

Answer 2

maybe you try it with setting the field not to be readonly anymore

In C#:

f.ReadOnlyField = false;
f.Update(true);
s.Lists[ListName].Update();
f.Delete();