使用Double Foreach循环输出数据时的相同结果

Question

I need to set a string into something like this

<Student>
    <StudentID></StudentID>
    <FirstName></FirstName>
    <Fees>
         <Fee>
             <FeeID></FeeID>
         </Fee>
    </Fees>
</Student>
<Student>
    <StudentID></StudentID>
    <FirstName></FirstName>
    <Fees>
         <Fee>
             <FeeID></FeeID>
         </Fee>
    </Fees>
</Student>
... and so on

My code

string strFeeData = ""; // XML Content for Fees
string strStuData = ""; // XML Content for Students with Fees

foreach (var studentData in sorted)
{
    foreach(Fee feeData in studentData.Fees)
    {
        strFeeData = strFeeData + "<Fee>\n\t<FeeID>" + feeData.FeeID + "</FeeID>\n\t<FeeName>" + feeData.FeeName + "</FeeName>\n\t<Amount>" + feeData.Amount + "</Amount>\n\t<DueDate>" + feeData.DueDate + "</DueDate>\n</Fee>\n";
    }
    strStuData = strStuData + "<Student>\n\t<StudentID>" + studentData.StudentID + "</StudentID>\n<FirstName>" + studentData.FirstName + "</FirstName>\n<LastName>" + studentData.LastName + "</LastName>\n<Grade>" + studentData.Grade + "</Grade>\n<Fees>\n\t" + strFeeData + "</Fees></Student>\n";
}

I got this part outputted correctly

<Student>
    <StudentID>1</StudentID>
    <FirstName>David</FirstName>
...
<Student>
    <StudentID>2</StudentID>
    <FirstName>John</FirstName>

But for Fees

<Fees>
     <Fee>
         <FeeID>12</FeeID>
....
<Fees>
     <Fee>
         <FeeID>12</FeeID>

I got the same Fees for every students.

What is wrong with my double foreach loop?

(I already checked sorted's Fee has different values, the problem must be at the double foreach loop)

Thanks

Answer 1

Initialize strFeeData with empty string within outer loop:

foreach (var studentData in sorted)
{
    strFeeData = "";

    foreach(Fee feeData in studentData.Fees)
    {
        strFeeData = strFeeData + "<Fee>\n\t<FeeID>" + feeData.FeeID + "</FeeID>\n\t<FeeName>" + feeData.FeeName + "</FeeName>\n\t<Amount>" + feeData.Amount + "</Amount>\n\t<DueDate>" + feeData.DueDate + "</DueDate>\n</Fee>\n";
    }
    strStuData = strStuData + "<Student>\n\t<StudentID>" + studentData.StudentID + "</StudentID>\n<FirstName>" + studentData.FirstName + "</FirstName>\n<LastName>" + studentData.LastName + "</LastName>\n<Grade>" + studentData.Grade + "</Grade>\n<Fees>\n\t" + strFeeData + "</Fees></Student>\n";
}

However, it's really bad idea to create XML using string concatenation! You should read about Serialization or LINQ to XML!

LINQ to XML version

var xml = sorted.Select(s => new XElement("Student"
                                 new XElement("StudentID", s.StudentID),
                                 new XElement("FirstName", s.FirstName),
                                 new XElement("LastName", s.LastName),
                                 new XElement("Fees",
                                    s.Fees.Select(f => new XElement("Fee",
                                                           new XElement("FeeID", f.FeeID))).ToArray())));

Answer 2

why dont you try out like this ,You can always use XmlSerializer to transform a list of C# objects to XML document.

public string ToXML()
    {
        var stringwriter = new System.IO.StringWriter();
        var serializer = new XmlSerializer(this.GetType());
        serializer.Serialize(stringwriter, this);
        return stringwriter.ToString();
    }

this seializ your class to xml string

Also check this : Convert a C# object to XML?

Linq To XML way

XElement _customers = new XElement("Students",
                       from c in objCust
                       orderby c.CustID //descending 
                        select new XElement("Student",
                            new XElement("name", c.StudentID),
                            new XElement("ID", c.FirstName),
                            new XElement("phone", c.LastName),
                            new XElement("Fees", (from x in x.Fees
                                                  orderby x.FeeID//descending 
                            select new XElement("FeeID",x.FeesId)) 
                        ))

                  );