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Link query

Posted on 2008-10-08
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Last Modified: 2013-12-17
Is there an easy way to get to the individual elements in the XML?

  XDocument books = new XDocument(
                                    new XElement("Books",
                                new XElement("book",
                                    new XElement("name", "Book 1"),
                                    new XElement("author", "John Doe")),
                                new XElement("book",
                                    new XElement("name", "Book 2"),
                                    new XElement("author", "Jane Doe"))));


 IEnumerable<XElement> elements;
            elements = books.Element("Books").Elements("book");


 foreach (XElement element in elements.Elements())
{
// Something like
element["name"].value;
element["author"].value;

// instead of looping - returns Book 1john Doe
element.value;

}

thanks


0
Comment
Question by:sansoftura
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9 Comments
 
LVL 21

Expert Comment

by:naspinski
ID: 22670135
you could simply do something like this:
foreach (XElement x in (from p in books.Descendants("book"))
  //loop here
 
//or if you just want the first one
XElement xe = (from p in books.Descendants("book").First();
//then just use it like this:
string value = xe.Value;
 
//Does that answer your question?

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0
 
LVL 6

Author Comment

by:sansoftura
ID: 22670457
Thanks. I just added 'select p' to your first for each
foreach (XElement x in (from p in books.Descendants("book") select p))

but still how do i get to each item in the element
x("name")
x("author")

?
0
 
LVL 63

Expert Comment

by:Fernando Soto
ID: 22670701
Hi sansoftura;

This code snippet will do what you want.

Fernando

            XDocument books = new XDocument(
                                    new XElement("Books",
                                        new XElement("book",
                                            new XElement("name", "Book 1"),
                                            new XElement("author", "John Doe")),
                                        new XElement("book",
                                            new XElement("name", "Book 2"),
                                            new XElement("author", "Jane Doe"))));
 
            var elements = from book in books.Document.Root.Elements("book")
                           select new
                           {
                               Name = book.Element("name").Value,
                               Author = book.Element("author").Value
                           };
 
            foreach (var element in elements)
                Console.WriteLine("Book Name = {0}\nBook Author = {1}",
                        element.Name, element.Author);

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LVL 6

Author Comment

by:sansoftura
ID: 22671779
Thanks that helped . But if i want to get the elements from the node books how do i get it?

say
<Books>
<book>
...
</book>
<book>
...
</book>
<ImportDate>1/1/1980</ImportDate>
<ImportUser>Fernando</ImportUser>
</Books>

How do i get to the other elements?

0
 
LVL 63

Expert Comment

by:Fernando Soto
ID: 22672300
Hi sansoftura;


There are a couple of approaches to this question:
1. you can do the query like the following:
 
   IEnumerable<XElement> elements = from book in books.Document.Root.Elements("book")
                                    select book;
 
then in the foreach loop you can get each node of type "book". Then for each element you can get it Descendants and print out its values. But this causes you to use XML to navigate the child nodes and pull out the values you need.
 
2. Another approache is to get the information you want in the select clause and return that as an Anonymous type as in the following.
 
   var elements = from book in books.Document.Root.Elements("book")
                  select new
                  {
                     Name = book.Element("name").Value,
                     Author = book.Element("author").Value,
                     ImportDate = book.Element("ImportDate").Value,
                     ImportUser = book.Element("ImportDate").Value
                  };
 
then in the foreach loop get the needed values as in the following code.
 
foreach (var element in elements)
   Console.WriteLine("Book Name = {0}\nBook Author = {1}\nImport Date = {2}\tImport User = {3}",
      element.Name, element.Author, element.ImportDate, element.ImportUser );
 
Note that in the select clause above, variable = node value, the variable name used here can be anything you want just like any other C# variable name and that is the name you use to access that value in the foreach loop.
 
Fernando

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0
 
LVL 6

Author Comment

by:sansoftura
ID: 22672865
Thanks Fernando. I tried the above method but i am not getting the value for the elements in book  (ImportDate, ImportUser)
            XElement books = new XElement(
                                    new XElement("Books",
                                       new XElement("ImportDate", "1/1/80"),
                                       new XElement("ImportUser", "Fernando"),
                                       new XElement("book",
                                    new XElement("name", "Book 1"),
                                    new XElement("author", "John Doe")),
                                new XElement("book",
                                    new XElement("name", "Book 2"),
                                    new XElement("author", "Jane Doe"))));
 
// Code works
          var elements = from book in books.Elements("book")
                           select new
                           {
                               name = book.Element("name").Value,
                               author = book.Element("author").Value
                           };
            foreach (var element in elements)
                MessageBox.Show("Book Name = " + element.name + "\nBook Author = " + element.author);
 
// End code works
 
// New Code that doesn't work
          
            var newElements = from book in books.Descendants()
                           select new
                           {
                               ImportDate = book.Element("ImportDate").Value,
                               ImportUser = book.Element("ImportUser").Value
                           };
 
            foreach (var importElement in newElements)
                MessageBox.Show("ImportDate = " + importElement.ImportDate + "\nImportUser = " + importElement.ImportUser);

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0
 
LVL 63

Accepted Solution

by:
Fernando Soto earned 500 total points
ID: 22673657
Because the new document now looks like this:

<Books>
  <ImportDate>1/1/80</ImportDate>
  <ImportUser>Fernando</ImportUser>
  <book>
    <name>Book 1</name>
    <author>John Doe</author>
  </book>
  <book>
    <name>Book 2</name>
    <author>Jane Doe</author>
  </book>
</Books>

ImportDate and ImportUser are at the same level as book. Then you would need to change the query in such a way to catch the needed nodes and if you had multiple nodes of ImportDate and ImportUser and wanted book as well it would become difficult to do. One way to get thoes two fields if they were to be the only nodes of there type would be as follows:

String importDate = books.Element("ImportDate").Value;
String importUser = books.Element("ImportUser").Value;

To query an XML document you need to know before hand the schema of the document and create the query from that.
0
 
LVL 6

Author Closing Comment

by:sansoftura
ID: 31504285
Thanks! that worked.

Just curious when we use  IEnumerable elements  to query the XML?

0
 
LVL 63

Expert Comment

by:Fernando Soto
ID: 22678814
Hi sansoftura;

To your question, "when we use  IEnumerable<XElement> elements  to query the XML?", The   elements variable is typed with IEnumerable<XElement> when the query parses the XML document and does not create an anonymous type like was done in one of the sample code. For example  in the following snippet oc code the return type is a collection of XElement and therefore you can use IEnumerable<XElement>:

IEnumerable<XElement> elements =
    from book in books.Document.Root.Elements("book")
    select book;

In the above the books document is queryed and each element that is parsed is placed into book variable and in the select statement a collection of book is created and returned which are still XElement. While in the following code this is not true:

var elements = from book in books.Document.Root.Elements("book")
               select new
               {
                   Name = book.Element("name").Value,
                   Author = book.Element("author").Value,
               };

The reason this is not true is that in the select clause we create a collection of an anonymous type by using the new keyword with the structure of that anonymous type,

      select new
               {
                   Name = book.Element("name").Value,
                   Author = book.Element("author").Value,
               };

Fernando

0

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