在解析xml“错误无序列元素”时检查元素是否存在

Question

i have an xml with different set tags, i want to check if an element exist since i am having error no sequence element How do i check if tag szSerialNmbr is present, if not assign a null value or escape the Transaction Descendants. I went through other post but getting error Error "Extension method must be defined in a non-generic static class"

XDocument xDocument = XDocument.Load(file);

foreach (var trans in xDocument.Descendants("Transaction"))
{
    var val1 = (string)trans.Descendants("Set").Elements("szSerialNmbr").First();

    var val2 = (string)trans.Descendants("Set").Elements("lMediaNmbr").First();

    var val3 = (string)trans.Descendants("Set").Elements("lMediaMember").First(); 
}

Answer 1

you can do a null check by adding a ? , also if you are not sure if your set will contain the object you are looking for in linq, you can use firstOrDefault to allow null as a return value.

var val1 = (string)trans?.Descendants("Set")?.Elements("szSerialNmbr")?.FirstOrDefault()?.Value;