The element A in namespace B has invalid child element C in namespace D

Question

I am getting the following error on validating XML

The element 'Root' in namespace 'http://www.test.com/test' has invalid child element 'Student' in namespace 'http://www.test.com/test'. List of possible elements expected: 'Student'.

I cannot post the actual XSD but I have prepared a small XSD to replicate the issue. Also, I have no control on XSD because it is provided by client. The sample XSD looks as follows.

<xs:schema xmlns:stu="http://www.test.com/test" 
           xmlns:xs="http://www.w3.org/2001/XMLSchema"      
           targetNamespace="http://www.test.com/test" 
           elementFormDefault="unqualified" 
           attributeFormDefault="unqualified" 
           version="1.2">
<xs:element name="Root">
<xs:complexType>
  <xs:sequence>
    <xs:element name="Student" type="stu:Student" minOccurs="1" maxOccurs="1">          
    </xs:element>
  </xs:sequence>
</xs:complexType>
</xs:element>
<xs:simpleType name="Date">
  <xs:restriction base="xs:date">
    <xs:minInclusive value="0001-01-01"/>
    <xs:maxInclusive value="9999-12-31"/>
    <xs:pattern value="\p{Nd}{4}-\p{Nd}{2}-\p{Nd}{2}"/>
  </xs:restriction>
</xs:simpleType>
<xs:simpleType name="String100">
  <xs:restriction base="xs:string">
    <xs:maxLength value="100"/>
    <xs:minLength value="1"/>
  </xs:restriction>
</xs:simpleType>
<xs:complexType name="Student">
  <xs:sequence>
    <xs:element name="StudentName" type="stu:String100" nillable="false"/>
    <xs:element name="AdmissionDate" type="stu:Date" nillable="false"/>
  </xs:sequence>
</xs:complexType>
</xs:schema>

I generate the XML based upon provided XSD and data I have. The XML is generated as follows.

<?xml version="1.0" encoding="utf-8"?>
<Root xmlns="http://www.test.com/test" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <Student>
        <StudentName>StudentName1</StudentName>
        <AdmissionDate>2010-01-01</AdmissionDate>
    </Student>
</Root>

I checked this thread on stackoverflow The element "x" in namespace "xSchema" has invalid child element "y" in namespace "xSchema". List of possible elements expected: "y" but it states that we should remove prefix use

<order> 

instead of

<os:order>. 

But in my case the XML is already being generated like that. How can i overcome this issue?

I also generated sample XML using Visual Studio from XSD to see what's the difference. The sample XML which validates has just one line different

<?xml version="1.0" encoding="utf-8"?>
<Root xmlns="http://www.test.com/test">
   <Student xmlns=""> <!-- JUST THIS xmlns="" ADDED prevents the issue -->
     <StudentName>StudentName1</StudentName>
     <AdmissionDate>2010-01-01</AdmissionDate>
   </Student>
</Root>

What difference does adding xmlns="" makes? I am looking for alternate solutions and cause of the issue. Please help.

Answer 1

This is a great question as it gets to the heart of how xml namespaces work.

The reason you have to set the xmlns="" on the Student element is because the schema specifies elementFormDefault="unqualified", which means that any element declared under the Root element resides in a "null" namespace.

Your desired instance:

<Root xmlns="http://www.test.com/test">
  <Student>
    <StudentName>f</StudentName>
    <AdmissionDate>0001-01-01</AdmissionDate>
  </Student>
</Root>

will not validate because Student inherits it's namespace from Root, and in the schema, Student does not belong to this namespace.

So, you have two options, either add the xmlns="" into the Student node (as you have already found out), or use a namespace prefix in your instance:

<x:Root xmlns:x="http://www.test.com/test">
  <Student>
    <StudentName>f</StudentName>
    <AdmissionDate>0001-01-01</AdmissionDate>
  </Student>
</x:Root>

Also, if your client changes the schema to make elementFormDefault="qualified" then your desired instance form would be valid.