Exception when reading a certain DataSet column loaded with the contents of an XML file

After performing some tests, it seems that DataSet.ReadXml is not able to correctly infer the data schema if there is a field whose name matches the name of the superior element. It is probably something inherent to the internal implementation of the method and the way of traversing the nodes to infer the schema of the data.

Having seen this, you have two options:

...
<NumCodigos>
   <NumCodigo>123456</NumCodigo>
</NumCodigos>

<?xml version="1.0" standalone="yes"?>
<NewDataSet>
  <xs:schema id="NewDataSet" xmlns="" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
    <xs:element name="NewDataSet" msdata:IsDataSet="true" msdata:UseCurrentLocale="true">
      <xs:complexType>
        <xs:choice minOccurs="0" maxOccurs="unbounded">
          <xs:element name="Productos">
            <xs:complexType>
              <xs:sequence>
                <xs:element name="P11" type="xs:int" minOccurs="0" />
                <xs:element name="P12" type="xs:int" minOccurs="0" />
                <xs:element name="P14" type="xs:int" minOccurs="0" />
                <xs:element name="P21" type="xs:int" minOccurs="0" />
              </xs:sequence>
            </xs:complexType>
          </xs:element>
          <xs:element name="Cantidades">
            <xs:complexType>
              <xs:sequence>
                <xs:element name="Tipo" type="xs:string" minOccurs="0" />
                <xs:element name="Producto" type="xs:string" minOccurs="0" />
                <xs:element name="NumCodigo" type="xs:int" minOccurs="0" />
              </xs:sequence>
            </xs:complexType>
          </xs:element>
          <xs:element name="NumCodigo">
            <xs:complexType>
              <xs:sequence>
                <xs:element name="NumCodigo" type="xs:int" minOccurs="0" />
              </xs:sequence>
            </xs:complexType>
          </xs:element>
        </xs:choice>
      </xs:complexType>
    </xs:element>
  </xs:schema>
  <Productos>
    <P11>1</P11>
    <P12>1</P12>
    <P14>1</P14>
    <P21>0</P21>
  </Productos>
  <Cantidades>
    <Tipo>A</Tipo>
    <Producto>P11</Producto>
    <NumCodigo>123456</NumCodigo>
  </Cantidades>
  <Cantidades>
    <Tipo>B</Tipo>
    <Producto>P12</Producto>
    <NumCodigo>123456</NumCodigo>
  </Cantidades>
  <Cantidades>
    <Tipo>C</Tipo>
    <Producto>P14</Producto>
    <NumCodigo>123456</NumCodigo>
  </Cantidades>
  <NumCodigo>
    <NumCodigo>123456</NumCodigo>
  </NumCodigo>
</NewDataSet>

If the xml file with the data is being generated by using DataSet.WriteXml , what you should do is add the XmlWriteMode.WriteSchema parameter to add the schema to the file:

ds.WriteXml(Server.MapPath("~/datos.xml"),XmlWriteMode.WriteSchema);

Edited

There is a third option, which you can use if (as it seems to be your case) you do not have access to modify the xml file. This option is to generate the data schema in your DataSet before importing it. I'm going to use the example you've put:

//Creamos las tablas y campos necesarios:

DataTable dt1 = new DataTable("Productos");
dt1.Columns.Add("P11", typeof(int));
dt1.Columns.Add("P12", typeof(int));
dt1.Columns.Add("P14", typeof(int));
dt1.Columns.Add("P21", typeof(int));

DataTable dt2 = new DataTable("Cantidades");
dt2.Columns.Add("Tipo");
dt2.Columns.Add("Producto");
dt2.Columns.Add("NumCodigo", typeof(int));

DataTable dt3 = new DataTable("NumCodigo");
dt3.Columns.Add("NumCodigo");

//Añadimos las tablas a un nuevo DataSet
DataSet ds = new DataSet();
ds.Tables.Add(dt1);
ds.Tables.Add(dt2);
ds.Tables.Add(dt3);

//Ahora en ds ya tenemos el esquema de datos correcto. Ya podemos importar los datos

ds.ReadXml(Server.MapPath("~/datos.xml"));
var col = ds.Tables["NumCodigo"].Rows[0]["NumCodigo"];

Using this method, you must bear in mind that the tables and fields that you generate must match the xml data schema, and if this varies, you must modify it in your code as well.

Issue 2

I think the optimal way to solve the problem in your case is to have the schema in an xsd file, and read it before importing the data. Summing up:

• You create a datos.xsd file with the schema:

  <xs:schema id="NewDataSet" xmlns="" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
  <xs:element name="NewDataSet" msdata:IsDataSet="true" msdata:UseCurrentLocale="true">
    <xs:complexType>
      <xs:choice minOccurs="0" maxOccurs="unbounded">
        <xs:element name="Productos">
          <xs:complexType>
            <xs:sequence>
              <xs:element name="P11" type="xs:int" minOccurs="0" />
              <xs:element name="P12" type="xs:int" minOccurs="0" />
              <xs:element name="P14" type="xs:int" minOccurs="0" />
              <xs:element name="P21" type="xs:int" minOccurs="0" />
            </xs:sequence>
          </xs:complexType>
        </xs:element>
        <xs:element name="Cantidades">
          <xs:complexType>
            <xs:sequence>
              <xs:element name="Tipo" type="xs:string" minOccurs="0" />
              <xs:element name="Producto" type="xs:string" minOccurs="0"/>
              <xs:element name="NumCodigo" type="xs:int" minOccurs="0" />
            </xs:sequence>
          </xs:complexType>
        </xs:element>
        <xs:element name="NumCodigo">
          <xs:complexType>
            <xs:sequence>
              <xs:element name="NumCodigo" type="xs:int" minOccurs="0" />
            </xs:sequence>
          </xs:complexType>
        </xs:element>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  </xs:schema>
  

• Now, we use the ReadXmlSchema method to first read the schema and then import the data:

  DataSet ds = new DataSet();
  //leemos el esquema
  ds.ReadXmlSchema(Server.MapPath("~/datos.xsd"));
  //importamos los datos
  ds.ReadXml(Server.MapPath("~/datos.xml"));
  //accedemos a la columna
  var col = ds1.Tables["NumCodigo"].Rows[0]["NumCodigo"];