CODEWITHSUNDEEP
c#linq-to-xml
Enigma34
Enigma34

Reputation: 347

linq to xml query: Object reference not set error while trying to retrieve child element

i am trying to retrieve all the child elements but getting System.Collections.ListDictionaryInternal. Object reference not set to an instance of an object error.

my c# code retrieve all the question on according to the test_id and category_id passed:-

public static List<Questions> GetQuestion_Catgy(int test_id, int ctgy_id)
        {
            try
            {
                XDocument data = XDocument.Load(docurl);
                return (from exm in data.Descendants("test_details")
                        where exm.Attribute("id").Value.Equals(test_id.ToString())
                        from ctgy in exm.Descendants("category")
                        where ctgy.Attribute("id").Value.Equals(ctgy_id.ToString())
                        orderby (int)ctgy.Attribute("id")
                        select new Questions
                        {
                            quesID = Convert.ToInt32(ctgy.Attribute("id").Value),
                            quesSTRING = ctgy.Attribute("ques").Value,
                            quesRATE = Convert.ToInt32(ctgy.Attribute("rating").Value),
                            quesOPT1 = (string)ctgy.Element("opt1").Value,
                            quesOPT2 = (string)ctgy.Element("opt2").Value,
                            quesOPT3 = (string)ctgy.Element("opt3").Value,
                            quesOPT4 = (string)ctgy.Element("opt4").Value,
                            quesANS = Convert.ToInt32(ctgy.Element("ans").Value),
                            quesIMG = (string)ctgy.Element("img").Value
                        }).ToList();
            }
            catch (Exception ex)
            {
                throw new ArgumentException(ex.Data + "\n" + ex.Message);
            }
        }

my xml

<test_details id="1" name="test exam" time="30" marks="100" difficulty="1">
    <category id="1" name="HTML">
      <question id="1" ques="what is HTML ?" rating="5">
        <opt1>Markup Language</opt1>
        <opt2>Scripting Language</opt2>
        <opt3>Server-Side Lanugae</opt3>
        <opt4>Client-Side Language</opt4>
        <ans>1</ans>
        <img>null</img>
      </question>
      <question id="2" ques="what is LMTH ?" rating="5">
        <opt1>Markup Language</opt1>
        <opt2>Scripting Language</opt2>
        <opt3>Server-Side Lanugae</opt3>
        <opt4>Client-Side Language</opt4>
        <ans>2</ans>
        <img>null</img>
      </question>
    </category>
    <category id="2" name="C#" />
  </test_details>

enter image description here

Upvotes: 0

Views: 395

Answers (3)

Jestin
Jestin

Reputation: 330

It looks like you need to go down an extra level to the 'question' elements if you want to access the ques attribute. ctgy will not have ques.

Upvotes: 1

e_ne
e_ne

Reputation: 8459

Your error is on this line:

from ctgy in exm.Descendants("category")

The exm elements are at the same level of your categories. You need to replace exm with data.

Example:

from ctgy in data.Descendants("category")

Upvotes: 0

AD.Net
AD.Net

Reputation: 13399

ctgy.Attribute("ques").Value
ctgy.Attribute("rating").Value

There is no such attribute.

Also do a null check before doing things like

(string)ctgy.Element("opt2").Value,

Upvotes: 0

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