Preserving Order In Sequence of Choices (LINQ To XSD)

Question

Given the following XML example we could imagine a schema defining Root as containing a sequence of unbound number of choices between Type1 and Type2.

<Root>
    <Type1 />
    <Type2 />
    <Type2 />
    <Type1 />
</Root>

I am testing out migrating from the XSD.exe tool which although adds type-safety has a lot of little annoyances. The XSD tool in this case just creates within Root an array of type System.Object and you have to figure out what type of objects (Type1 or Type2) are in there. Its not completely elegant, but at least you preserve order.

The problem is when LINQ to XSD creates the objects, it defines Root as having two independent lists of Type1 and Type2. This is great in that it is type-safe, but I now appear to lose the order of the elements. I built LINQ to XSD from the source on codeplex.

Using LINQ to XSD, how can I preserve the order of these elements?

Answer 1

How about creating a wrapper around Choice? Limiting the types that it accesses like this:

class Choice
{
    private object _value;

    public ChoiceEnum CurrentType { get; private set; }

    public Type1 Type1Value
    {
        get { return (Type1) _value; }
        set { _value = value; CurrentType = ChoiceEnum.Type1; }
    }

    public Type2 Type2Value
    {
        get { return (Type2) _value; }
        set { _value = value; CurrentType = ChoiceEnum.Type2; }
    }
}

This is a simplified version, and you will have to add more validation (if _value is of correct type, what is the current type of _value, etc).

Then, you can filter it with LINQ:

var q1 = from v in root.Sequence
         where v.CurrentType == ChoiceEnum.Type1
         select v.Type1;

Or you can create methods in Root that will wrap the queries.

Answer 2

Linq2Xsd only trips up on sequences when there's an xsd:choice element.

Fortunately I was able to remove the xsd:choice for the Amazon XSD I am using (I just wasn't using MerchantOrderID), which allowed the sequence to properly be preserved in the ToString() for the xml.

            <xsd:choice>                                <--- removed line
                <xsd:element ref="AmazonOrderID"/>
                <xsd:element ref="MerchantOrderID"/>    <--- removed line
            </xsd:choice>                               <--- removed line

            <xsd:element name="ActionType" minOccurs="0" maxOccurs="1">
                <xsd:simpleType>
                    <xsd:restriction base="xsd:string">
                        <xsd:enumeration value="Refund"/>
                        <xsd:enumeration value="Cancel"/>
                    </xsd:restriction>
                </xsd:simpleType>
            </xsd:element> 

The generated code then correctly has this in the constructor which preserves the order

contentModel = new SequenceContentModelEntity(
               new NamedContentModelEntity(XName.Get("AmazonOrderID", "")), 
               new NamedContentModelEntity(XName.Get("ActionType", "")), 
               new NamedContentModelEntity(XName.Get("CODCollectionMethod", "")), 
               new NamedContentModelEntity(XName.Get("AdjustedItem", "")));

You may also be able to do this manually by subclassing it youself, but I'm not sure how this would work with an xsd:choice. This is described here but I haven't tested it.