NullableTypes over Web Services

nbhatia · **Joined:** Sun Sep 25, 2005 11:35 pm **Posts:** 57

I am looking for a solution to store NULL values in my entities. I came across the NullableTypes library by looking at this formum's postings. I do have a quick question before I jump into using them. Has anybody tried to send these values over a Web Service? Does that work as smoothly as the .NET value types, i.e. do the values get serialized / deserialized on both client and server end without any hassles?

Thanks.

KPixel · **Posted:** Tue Oct 04, 2005 11:23 am

AFAIK, it should work perfectly well :)

nbhatia · **Joined:** Sun Sep 25, 2005 11:35 pm **Posts:** 57

OK, I tried using NullDateTime in a Web Service, but the WSDL that is generated looks like this:

Code:

<s:complexType name="Trade">
  <s:sequence>
    <s:element minOccurs="1" maxOccurs="1" name="Id" type="s:long" /> 
    <s:element minOccurs="1" maxOccurs="1" name="ExpirationTime" type="tns:NullableDateTime" /> 
  </s:sequence>
</s:complexType>

<s:complexType name="NullableDateTime" /> 

Note the definition for NullableDateTime contains an empty implementation. What am I doing wrong?

luggage · **Posted:** Thu Nov 03, 2005 3:52 pm

I believe the Nullable Types need to have some attributes on the properties to make sure it is serialized correctly. I'm testing it now.

There is going to be an issue with compatibility with other languages that consume the web service if you want to keep it completely standard.

luggage · **Posted:** Fri Nov 04, 2005 10:48 am

OK, it is the fact that all of the properties are read-only that it doesn't work.

Making the properties writable will change the way the Nullables work too much, so I am going to try implementing IXmlSerializable on the unllable types to handle it.

The other trick is getting it to use the Nullables library on the client side and not some automatically generated class with public fields. I'm looking into that also.

luggage · **Posted:** Fri Nov 04, 2005 1:36 pm

I've been playing with XmlSerializable and came up with this to make it show up in the wsdl:

This is in NullableInt32:

Code:

      #region IXmlSerializable Members

      public void WriteXml(System.Xml.XmlWriter writer)
      {
         writer.WriteElementString("HasValue", hasValue.ToString());
         if (hasValue)
            writer.WriteElementString("Value", _value.ToString());
      }

      public System.Xml.Schema.XmlSchema GetSchema()
      {
         XmlSchema s = new XmlSchema();

         s.Id = "nullables-int32"; //i don't know what this does, but an Id is required.

         XmlSchemaElement hasValueElement = new XmlSchemaElement();
         hasValueElement.Name = "HasValue";
         hasValueElement.SchemaTypeName = new XmlQualifiedName("boolean", "http://www.w3.org/2001/XMLSchema");
         hasValueElement.MinOccurs = 1;
         hasValueElement.MaxOccurs = 1;
         s.Items.Add(hasValueElement);

         XmlSchemaElement valueElement = new XmlSchemaElement();
         valueElement.Name = "Value";
         valueElement.SchemaTypeName = new XmlQualifiedName("int", "http://www.w3.org/2001/XMLSchema");
         valueElement.MinOccurs = 0;
         valueElement.MaxOccurs = 1;
         s.Items.Add(valueElement);
         
         return s;
      }

      public void ReadXml(System.Xml.XmlReader reader)
      {
         // TODO:  Add NullableInt32.ReadXml implementation
      }

      #endregion

Unfortunately this will still create some new dummy NullableInt32 on the client side. I'm working on causing it to deserialize to the existing NullableInt32.