Having trouble with adding one property to an object inside a list after assigning the rest of them

I’ve been having trouble (again) with some object-oriented code.

Currently I have a piece of code that populates a list with objects and its properties that goes like this:

foreach (var folder in pathList)
{
    DirectoryInfo di = new DirectoryInfo(folder);
    foreach (var file in di.GetFiles())
    {
        fileinfoList.Add(new FileInfo()
            {
                partNumber = Path.GetFileNameWithoutExtension(Convert.ToString(file)),
                fileType = Path.GetExtension(Convert.ToString(file)),
                lastDate = file.LastWriteTime,
                released = 1,
                checkedBy = null,
                fullPath = Path.GetFullPath(Convert.ToString(folder)),
            });
    }
}

What I need is to add the baseID property to each of the objects. This is what I have currently:

foreach (var item in fileNameList)
{
    if (fileinfoList.Select(m => m.partNumber == dummyString.ToString()) != null)
    {
        SqlConnection conn = new SqlConnection();
        conn.ConnectionString = @"data source = MYPCSQLEXPRESS; database = MYDB; integrated security = TRUE";
        string query = $@"SELECT id FROM MYTABLE WHERE fullpath= '{pathsToFilesNotOnDbList[y]}' ";
        var cmd = new SqlCommand(query, conn);
        conn.Open();
        SqlDataReader dataReader = cmd.ExecuteReader();
        while (dataReader.Read())
        {
            iD = Convert.ToInt16(dataReader["id"]);
            fileinfoList.Select (f => f.baseID = iD) ;
            Console.WriteLine(y);
            y++;
        }
        conn.Close();
    }
}

I want this loop to take the value of iD and assign it to the baseID property.

I can get the iD‘s just fine, however I’m aware that the lambda expression fileinfoList.Select (f => f.baseID = iD) does nothing currently.

Can someone help me out?

Answer

If you want to set baseId = iD to all the elements of the list fileinfoList, just use:

fileinfoList.ForEach(i => i.baseID = iD);

UPDATE: set different id to each element:

var index = 0;
while (dataReader.Read())
{
    iD = Convert.ToInt16(dataReader["id"]);
    fileinfoList[index].baseID = id;
    Console.WriteLine(y);
    y++;
    index++;
}