Question

I have two methods that almost do the same thing. They get a List<XmlNode> based on state OR state and schoolType and then return a distinct, ordered IEnumerable<KeyValuePair<string,string>>. I know they can be refactored but I’m struggling to determine what type the parameter should be for the linq statement in the return of the method (the last line of each method).

I thank you for your help in advance.

private IEnumerable<KeyValuePair<string, string>> getAreaDropDownDataSource() {
    StateInfoXmlDocument stateInfoXmlDocument = new StateInfoXmlDocument();
    string schoolTypeXmlPath = string.Format(STATE_AND_SCHOOL_TYPE_XML_PATH, StateOfInterest, ConnectionsLearningSchoolType);
    var schoolNodes = new List<XmlNode>(stateInfoXmlDocument.SelectNodes(schoolTypeXmlPath).Cast<XmlNode>());
    return schoolNodes.Select(x => new KeyValuePair<string, string>(x.Attributes["idLocation"].Value, x.Value)).OrderBy(x => x.Key).Distinct();
}

private IEnumerable<KeyValuePair<string, string>> getStateOfInterestDropDownDataSource() {
    StateInfoXmlDocument stateInfoXmlDocument = new StateInfoXmlDocument();
    string schoolTypeXmlPath = string.Format(SCHOOL_TYPE_XML_PATH, ConnectionsLearningSchoolType);
    var schoolNodes = new List<XmlNode>(stateInfoXmlDocument.SelectNodes(schoolTypeXmlPath).Cast<XmlNode>());
    return schoolNodes.Select(x => new KeyValuePair<string, string>(x.Attributes["stateCode"].Value, x.Attributes["stateName"].Value)).OrderBy(x => x.Key).Distinct();
}

Answer 1

Extract nodes retrieving to separate methods/properties. I also suggest to have different properties/methods for extracting school and state nodes:

private List<XmlNode> GetNodes(string xPath)
{
    XmlDocument stateInfoXmlDocument = new XmlDocument();
    return new List<XmlNode>(stateInfoXmlDocument.SelectNodes(xPath)
                                                 .Cast<XmlNode>());
}

private List<XmlNode> SchoolNodes
{
    get { return GetNodes(String.Format(SCHOOL_PATH, LearningSchoolType)); }
}

private List<XmlNode> StateNodes
{
    get { return GetNodes(String.Format(STATE_PATH, StateOfInterest)); }
}   

Use union of school and state nodes for retrieving area nodes:

private IEnumerable<KeyValuePair<string, string>> GetAreaDropDownDataSource()
{
    return SchoolNodes.Union(StateNodes)
            .Select(x => new KeyValuePair<string, string>(x.Attributes["idLocation"].Value, x.Value))
            .OrderBy(x => x.Key)
            .Distinct();
}

private IEnumerable<KeyValuePair<string, string>> GetStateOfInterestDropDownDataSource()
{
    return SchoolNodes
        .Select(x => new KeyValuePair<string, string>(x.Attributes["stateCode"].Value, x.Attributes["stateName"].Value))
        .OrderBy(x => x.Key)
        .Distinct();
}

Also you can use different selectors of type Func<XmlNode, KeyValuePair<string, string>> and pass them to method which will create data source:

private IEnumerable<KeyValuePair<string, string>> GetDropDownDataSource(
        List<XmlNode> nodes,
        Func<XmlNode, KeyValuePair<string, string>> selector)
{
    return nodes.Select(selector)
                .OrderBy(x => x.Key)
                .Distinct();
}