Question

I have the following XML file:

<?xml version="1.0" encoding="utf-8" ?>
<strategies>

  <strategy name="God Class">
    <gate type="AND">
      <rule>
        <metric>LOC</metric>
        <comparison>greater than</comparison>
        <value>850</value>
      </rule>
      <rule>
        <metric>FANIN</metric>
        <comparison>greater than</comparison>
        <value>850</value>
      </rule>
      <rule>
        <metric>FANOUT</metric>
        <comparison>greater than</comparison>
        <value>850</value>
      </rule>
    </gate>
  </strategy>

  <strategy name="TClass">
    <gate type="OR">
      <gate type="AND">
        <rule>
          <metric>LOC</metric>
          <comparison>greater than</comparison>
          <value>100</value>
        </rule>
        <rule>
          <metric>NOM</metric>
          <comparison>greater than</comparison>
          <value>200</value>
        </rule>
      </gate>
      <rule>
        <metric>NOPAR</metric>
        <comparison>greater than</comparison>
        <value>300</value>
      </rule>
    </gate>
  </strategy>

</strategies>

Now I try to parse this document and extract the rules. The first strategy is easy with the following code:

public static void parseRules()
        {
            XDocument document = XDocument.Load(FILE);
            XElement root = document.Root;

            foreach (XElement elem in root.Elements())
            { 
                String name = elem.Attribute(STRATEGY_NAME).Value;
                XElement gate = elem.Element(GATE_NAME);

                List<Rule> rules = new List<Rule>();
                foreach (XElement r in gate.Elements())
                {
                        String metric = r.Element(METRIC_NAME).Value;
                        String comparisation = r.Element(COMPARISON_NAME).Value;
                        int threshold = Convert.ToInt32(r.Element(VALUE_NAME).Value);

                        Rule rule = null;

                        if (comparisation.Equals(GREATER_THAN_NAME))
                        {
                            rule = new Rule(metric, Rule.GREATHER_THAN, threshold);
                        }
                        else if (comparisation.Equals(SMALLER_THAN_NAME))
                        {
                            rule = new Rule(metric, Rule.SMALLER_THAN, threshold);
                        }
                        rules.Add(rule);   
                }
                ISpecification spec = rules.ElementAt(0);
                if (gate.Attribute(TYPE_NAME).Value.Equals(AND))
                {
                    for (int i = 1; i < rules.Count; i++)
                    {
                        spec = spec.And(rules.ElementAt(i));
                    }
                }
                else if (gate.Attribute(TYPE_NAME).Value.Equals(OR))
                {
                    for (int i = 1; i < rules.Count; i++)
                    {
                        spec = spec.Or(rules.ElementAt(i));
                    }   
                }
                DetectionStrategy strategy = new DetectionStrategy(spec, name);
            }
        }
    }

Obviously this only works for XML files that have only rules in one gate and not another gate as in the second example. However I’m not able to parse nested gates. Any hints where to start?

Answer 1

Using XDocument or XmlDocument to parse the XML will be very brittle.

I suggest that you design a object model which will cater for this structure and logic and use the XML serialisation/deserialisation to persist or hydrate.

At the end of the day, this XML representation is only one possible representation of your logic, you could have them as JSON, Binary, …

An exmple:

public class Strategy
{
    [XmlAttribute]
    public string Name {get; set;}

    [XmlElement("Gate")]
    public Gate MainGate {get; get}
}
/// ...........

public class Gate
{

    XmlElement("Gate")
    public Gate ChildGate {get; set;}
    // ...
}    

---

UPDATE

Here is how you serialise (easy-peasy)

XmlSerializer xs = new XmlSerializer(typeof(Strategy));
FileStream fs = new FileStream("strategy.xml", FileMode.Create);
xs.Serialize(fs, myStrategy);