Serializable dictionary, how to set key name?

Question

Question: I use a serializable dictionary class, found at http://weblogs.asp.net/pwelter34/archive/2006/05/03/444961.aspx , to serialize a dictionary. Which works fine, but I run into an annoying problem.

      <System.Xml.Serialization.XmlRoot("DataBase")> _
    Public Class cDataBase
        <System.Xml.Serialization.XmlNamespaceDeclarations()> _
        Public ns As New System.Xml.Serialization.XmlSerializerNamespaces()


        <System.Xml.Serialization.XmlElement("Tables")> _
        Public Tables1 As New SerializableDictionary(Of String, cTable)


    End Class ' cDataBase

When I serialize instances of the above class, as this, the created xml looks like this:

<Tables>
<item>
  <key>
    <string>MyTable</string>
  </key>
  <value>
    <Table CreationDate="0001-01-01T00:00:00" LastModified="0001-01-01T00:00:00">
      <Columns>
        <Column Name="PrimaryKeyName">
          <DataType>Uniqueidentifier</DataType>
          <Length>36</Length>
        </Column>
      </Columns>
      <Rows>
        <Row>
          <Item>Reihe1</Item>
          <Item>Reihe2</Item>
          <Item>Reihe3</Item>
        </Row>
        <Row>
          <Item>Reihe1</Item>
          <Item>Reihe2</Item>
          <Item>Reihe3</Item>
        </Row>

Which would be good if only I could figure out how to rename the key from <string> to something defined in an attribute

  <key>
    <string>MyTable</string>
  </key>

Basically something like the XmlArrayItem attribute, such as below, if (only) the dictionary were an array...

        <System.Xml.Serialization.XmlArray("Tables")> _
        <System.Xml.Serialization.XmlArrayItem("Table")> _
        Public Tables As New List(Of cTable)

I wanted to try to change Of String to a custom class inherited from string, which I could equip with a name, but the problem is, one cannot inherit from string...

Answer 1

If I'm reading your question correctly, you want to change your serialized output from this:

<Tables>
  <item>
    <key>
      <string>MyTable</string>
    </key>
    <value>
      <!-- snip -->
    </value>
  </item>
</Tables>

To something like this:

<Tables>
  <item>
    <key>
      <TableId>MyTable</TableId>
    </key>
    <value>
      <!-- snip -->
    </value>
  </item>
</Tables>

You also mention that one way you could achieve this would be to create your own type which inherited from System.String, which - as you also mention - obviously isn't possible because it's sealed.

You can however achieve the same result by encapsulating the key value in your own type, and then controlling the XmlSerializer output using an XmlTextAttribute (see MSDN):

By default, the XmlSerializer serializes a class member as an XML element. However, if you apply the XmlTextAttribute to a member, the XmlSerializer translates its value into XML text. This means that the value is encoded into the content of an XML element.

In your case you'd use the attribute as follows:

public class TableId
{
    [XmlText]
    public string Name
    {
        get;
        set;
    }
}

And then use this type as the key(s) to your Dictionary. Which should achieve what you want.