Question

I have this XML file:

<MyXml>
    <MandatoryElement1>value</MandatoryElement1>
    <MandatoryElement2>value</MandatoryElement2>
    <MandatoryElement3>value</MandatoryElement3>
    <CustomElement1>value</CustomElement1>
    <CustomElement2>value</CustomElement2>
<MyXml>

All 3 elements that are called ‘MandatoryElementX’ will always appear in the file. The elements called ‘CustomElementX’ are unknown. These can be added or removed freely by a user and have any name.

What I need is to fetch all the elements that are not MandatoryElements. So for the file above I would want this result:

<CustomElement1>value</CustomElement1>
<CustomElement2>value</CustomElement2>

I don’t know what the names of the custom elements may be, only the names of the 3 MandatoryElements, so the query needs to somehow exclude these 3.

Edit:
Even though this was answered, I want to clarify the question. Here is an actual file:

<Partner>
    <!--Mandatory elements-->
    <Name>ALU FAT</Name>
    <InterfaceName>Account Lookup</InterfaceName>
    <RequestFolder>C:\Documents and Settings\user1\Desktop\Requests\ALURequests</RequestFolder>
    <ResponseFolder>C:\Documents and Settings\user1\Desktop\Responses</ResponseFolder>
    <ArchiveMessages>Yes</ArchiveMessages>
    <ArchiveFolder>C:\Documents and Settings\user1\Desktop\Archive</ArchiveFolder>
    <Priority>1</Priority>

    <!--Custom elements - these can be anything-->
    <Currency>EUR</Currency>
    <AccountingSystem>HHGKOL</AccountingSystem>
</Partner>

The result here would be:

<Currency>EUR</Currency>
<AccountingSystem>HHGKOL</AccountingSystem>

Answer 1

You can define a list of mandatory names and use LINQ to XML to filter:

 var mandatoryElements = new List<string>() {
                   "MandatoryElement1", 
                   "MandatoryElement2", 
                   "MandatoryElement3"
                };

 var result = xDoc.Root.Descendants()
                  .Where(x => !mandatoryElements.Contains(x.Name.LocalName));