检查列表内部对象的最佳方法是 null

Question

I am forming an object based on list coming from input along with the string like as below.

public static LibrarySourceTableInput CreateLibrarySourceTableInput<T>(List<T> libraries, string mechanicalLibraryName)
    where T : ISourceOfData
{
    return new LibrarySourceTableInput()
    {
        LibrarySourceRowInputs = libraries?.Select(l => new LibrarySourceRowInput()
        {
            LibrarySourceId = l.Id,
            SourceOfDataId = l.SourceOfData.Id
        }).ToList() ?? new(),
        MappedLibrarySource = mechanicalLibraryName
    };        
}

I am facing different problem here, I have libraries count coming as 1 but internal object is null for example in the below image libraries count as 1 and it is null,

and in this case I am getting a null reference exception with the above code, could any one please help on this how to avoid that null exception. Many thanks in advance.

Answer 1

You could do a where query before the select.

LibrarySourceRowInputs = libraries?.Where(l => l != null)
                                   .Select(l => l => new LibrarySourceRowInput()
                                              {
                                               LibrarySourceId = l.Id,
                                               SourceOfDataId = l.SourceOfData.Id
                                              }).ToList() ?? new();