To find an answer.

    questions.SelectMany(q =&gt; q.Answers).Where(a =&gt; a.Name == &quot;SomeName&quot;)

To find the question of an answer.

    questions.Where(q =&gt; q.Answers.Any(a =&gt; a.Name == &quot;SomeName&quot;))

In fact you will get collections of answers or questions and you will have to use `First()`, `FirstOrDefault()`, `Single()`, or `SingleOrDefault()` depending on your needs to get one specific answer or question.

    from question in Questions
    from answer in question.Answers
    where answer.Name == something
    select question // or select answer


Use the SelectMany and First/FirstOrDefault (if you are needing one value)

    List&lt;Questions&gt; questions = //initialization;
    var someAnswer = questions.SelectMany(q=&gt;q.Answers)
                              .First(a=&gt;a.Name ==&quot;MyName&quot;);

It seems you could use something like this:

    var query = from q in questions
                from a in q.Answers
                where a.Name == &quot;Answer Name&quot;
                select a;

I am not sure if this is possible but I want to iterate through a class and set a field member property without referring to the field object explicitly:

    public class Employee
    {
      public Person _person = new Person();
    	
      public void DynamicallySetPersonProperty()
      {
        MemberInfo[] members = this.GetType().GetMembers();
    
        foreach (MemberInfo member in members.Where(a =&gt; a.Name == &quot;_person&quot;))
        //get the _person field
        {
    
          Type type = member.GetType();
          PropertyInfo prop = type.GetProperty(&quot;Name&quot;); //good, this works, now to set a value for it
    
          //this line does not work - the error is &quot;property set method not found&quot;
          prop.SetValue(member, &quot;new name&quot;, null);
        }
      }
    }
    
    
    public class Person
    {
      public string Name { get; set; }
    }



In the answer that I marked as the answer you need to add:

      public static bool IsNullOrEmpty(this string source)
      {
        return (source == null || source.Length &gt; 0) ? true : false;
      }


c# - How to iterate through classes fields and set properties

How can I determine if a Cocoa `NSNumber` represents NaN (*not a number*)?

This emerges, for example, when I parse a string that has an invalid (non-numeric) contents.

Determine if NSNumber is NaN

I have a **Question** class that has public List property that can contain several **Answers**.

I have a question repository which is responsible for reading the questions and its answers from an xml file.

So I have a collection of Questions (List&lt;Question&gt;) with each Question object having a collection of Answers and I&#39;d like to query this collection of Questions for an Answer (ie by its Name) by using Linq. I don&#39;t know how to do this properly.

I could do it with a foreach but I&#39;d like to know whether there is a pure Linq way since I&#39;m learning it.







linq question: querying nested collections

I have a Question class that has public List property that can contain several Answers.
I have a question repository which is responsible for reading the questions and its answers from an xml file.
So I have a collection of Questions (List<question>) with each Question object having a collection of Answers and I'd like to query this collection of Questions for an Answer (ie by its Name) by using Linq. I don't know how to do this properly.</question>
I could do it with a foreach but I'd like to know whether there is a pure Linq way since I'm learning it.

Is there some mechanism by which I can be notified (in C#) when a file is modified on the disc?

Notification when a file changes?

I have `MyClass&lt;T&gt;`.

And then I have this `string s = &quot;MyClass&lt;AnotherClass&gt;&quot;;`. How can I get Type from the string `s`?

One way (ugly) is to parse out the &quot;&lt;&quot; and &quot;&gt;&quot; and do: 
 
    Type acType = Type.GetType(&quot;AnotherClass&quot;);  
    Type whatIwant = typeof (MyClass&lt;&gt;).MakeGenericType(acType);

But is there a cleaner way to get the final type without any parsing, etc.?


How can I get generic Type from a string representation?

I have a DataTable which has some rows and I am using the select to filter the rows to get a collection of DataRows which I then loop through using foreach and add it to another DataTable, but it is giving me the error &quot;This Row already belongs to another table&quot;.  Here is the code:

    DataTable dt = (DataTable)Session[&quot;dtAllOrders&quot;];
    DataTable dtSpecificOrders = new DataTable();
            
    DataRow[] orderRows = dt.Select(&quot;CustomerID = 2&quot;);

    foreach (DataRow dr in orderRows)
    {
        dtSpecificOrders.Rows.Add(dr); //Error thrown here.
    }

This Row already belongs to another table error when trying to add rows?

How can I detect that a client has disconnected from my server?

I have the following code in my `AcceptCallBack` method

    static Socket handler = null;
    public static void AcceptCallback(IAsyncResult ar)
    {
      //Accept incoming connection
      Socket listener = (Socket)ar.AsyncState;
      handler = listener.EndAccept(ar);
    }

I need to find a way to discover as soon as possible that the client has disconnected from the `handler` Socket.

I&#39;ve tried:

 1. `handler.Available;`
 2. `handler.Send(new byte[1], 0,
    SocketFlags.None);`
 3. `handler.Receive(new byte[1], 0,
    SocketFlags.None);`

The above approaches work when you are connecting to a server and want to detect when the server disconnects but they do not work *when you are the server and want to detect client disconnection.*

Any help will be appreciated.

Instantly detect client disconnection from server socket

POCO = Plain Old CLR (or better: Class) Object

DTO = Data Transfer Object



In this [post][1] there is a difference, but frankly most of the blogs I read describe POCO in the way DTO is defined: DTOs are simple data containers used for moving data between the layers of an application.

Are POCO and DTO the same thing?



  [1]: http://rlacovara.blogspot.com/2009/03/what-is-difference-between-dto-and-poco.html


Plain Old CLR Object vs Data Transfer Object

I&#39;m currently researching methods for storing user roles and permissions for .NET based projects. Some of these projects are web based, some are not. I&#39;m currently struggling to find the best method to achieve what I&#39;m looking for in a consistent, portable way across project types.

Where I&#39;m at, we&#39;re looking to leverage Active Directory as our single point of contact for basic user information. Because of this, we&#39;re looking to not have to maintain a custom database for each application&#39;s users since they are already stored in Active Directory and actively maintained there. Additionally, we don&#39;t want to write our own security model/code if possible and would like to use something pre-existing, like the security application blocks provided by Microsoft.

Some projects require only basic privileges, such as read, write, or no access. Other projects require more complex permissions. Users of those applications might be granted access to some areas, but not others, and their permissions can change across each area. An administration section of the app would control and define this access, **not** the AD tools. 

Currently, we&#39;re using integrated Windows Authentication to perform authentication on our intranet. This works well for finding out basic user information, and I&#39;ve seen that ASP.NET can be extended to provide an Active Directory roles provider, so I can find out any security groups a user belongs to. But, what seems like the downfall of this method to me is that everything is stored in Active Directory, which could lead to a mess to maintain if things grow too big. 

Along this same line, I&#39;ve also heard of Active Directory Lightweight Directory Services, which seems like it could extend our schema and add only application specific attributes and groups. Problem is, I can&#39;t find anything on how this would be done or how this works. There are MSDN articles that describe how to talk to this instance and how to create a new instance, but nothing ever seems to answer my question.

**My question is:** Based on your experience, am I going down the right track? Is what I&#39;m looking to do possible using just Active Directory, or do other tools have to be used?

----------

**Other methods I&#39;ve looked into:**

 - Using multiple web.config files [[stackoverflow][1]]
 - Creating a custom security model and database to manage users across applications


  [1]: https://stackoverflow.com/questions/176338/customer-configurable-asp-net-web-site-security-for-fine-grained-control-of-page

User Group and Role Management in .NET with Active Directory

How do I convert from excel serial date to a .NET date time?


For example  39938 is 05/05/2009.


How do I convert an Excel serial date number to a .NET DateTime?

Since there&#39;s no `button.PerformClick()` method in WPF, is there a way to click a WPF button programmatically?

How to programmatically click a button in WPF?

I have the name of the &quot;sort by property&quot; in a string. I will need to use Lambda/Linq to sort the list of objects.

Ex:

    public class Employee
    {
      public string FirstName {set; get;}
      public string LastName {set; get;}
      public DateTime DOB {set; get;}
    }
    
    
    public void Sort(ref List&lt;Employee&gt; list, string sortBy, string sortDirection)
    {
      //Example data:
      //sortBy = &quot;FirstName&quot;
      //sortDirection = &quot;ASC&quot; or &quot;DESC&quot;

      if (sortBy == &quot;FirstName&quot;)
      {
        list = list.OrderBy(x =&gt; x.FirstName).toList();    
      }
    
    }

1. Instead of using a bunch of ifs to check the fieldname (sortBy), is there a cleaner way of doing the sorting
2. Is sort aware of datatype?

Sorting a list using Lambda/Linq to objects

Is there a way in Linq to do an OrderBy against a set of values (strings in this case) without knowing the order of the values?

Consider this data:

    A
    B
    A
    C
    B
    C
    D
    E

And these variables:

string firstPref, secondPref, thirdPref;

When the values are set like so:

    firstPref = &#39;A&#39;;
    secondPref = &#39;B&#39;;
    thirdPref = &#39;C&#39;;

Is it possible to order the data like so:

    A
    A
    B
    B
    C
    C
    D
    E

Linq OrderBy against specific values

I have a dictionary of type 

    Dictionary&lt;Guid,int&gt;

I want to return the first instance where a condition is met using 

    var available = m_AvailableDict.FirstOrDefault(p =&gt; p.Value == 0)

However, how do I check if I&#39;m actually getting back a KeyValuePair? I can&#39;t seem to use != or == to check against default(KeyValuePair&lt;Guid,int&gt;) without a compiler error.  There is a similar thread [here][1] that doesn&#39;t quite seem to have a solution. I&#39;m actually able to solve my particular problem by getting the key and checking the default of Guid, but I&#39;m curious if there&#39;s a good way of doing this with the keyvaluepair. Thanks


  [1]: https://stackoverflow.com/questions/648115/how-can-an-object-not-be-compared-to-null

Check if KeyValuePair exists with LINQ&#39;s FirstOrDefault

&gt; **Possible Duplicate:**  
&gt; [Why is there not a ForEach extension method on the IEnumerable interface?](https://stackoverflow.com/questions/101265/why-is-there-not-a-foreach-extension-method-on-the-ienumerable-interface)  

&lt;!-- End of automatically inserted text --&gt;

I&#39;ve noticed when writing LINQ-y code that `.ForEach()` is a nice idiom to use.  For example, here is a piece of code that takes the following inputs, and produces these outputs:

    { &quot;One&quot; } =&gt; &quot;One&quot;
    { &quot;One&quot;, &quot;Two&quot; } =&gt; &quot;One, Two&quot;
    { &quot;One&quot;, &quot;Two&quot;, &quot;Three&quot;, &quot;Four&quot; } =&gt; &quot;One, Two, Three and Four&quot;;

And the code:

    private string InsertCommasAttempt(IEnumerable&lt;string&gt; words)
    {
        List&lt;string&gt; wordList = words.ToList();
        StringBuilder sb = new StringBuilder();
        var wordsAndSeparators = wordList.Select((string word, int pos) =&gt;
            {
                if (pos == 0) return new { Word = word, Leading = string.Empty };
                if (pos == wordList.Count - 1) return new { Word = word, Leading = &quot; and &quot; };
                return new { Word = word, Leading = &quot;, &quot; };
            });

        wordsAndSeparators.ToList().ForEach(v =&gt; sb.Append(v.Leading).Append(v.Word));
        return sb.ToString();
    }

Note the interjected `.ToList()` before the `.ForEach()` on the second to last line.

Why is it that `.ForEach()` isn&#39;t available as an extension method on `IEnumerable&lt;T&gt;`?  With an example like this, it just seems weird.


Why is .ForEach() on IList&lt;T&gt; and not on IEnumerable&lt;T&gt;?

I am trying to delete a selected gridview row using LINQ (No
LINQDataSource).

When the selection is changed, the detailsview binding is changed
also. I can add a new entry to the database, but when I added this
code to a delete button inside the updatePanel, I got an exception:

    try
    {    		
        var query = from i in db.QuestionModules 
                    where i.QuestionModuleID == QuestionModuleID 
                    select i;
                    
        QuestionModule o = query.First();
        db.QuestionModules.DeleteOnSubmit(o);
        db.SubmitChanges();
    }


This is the exception I get:

    System.Data.Linq.ChangeConflictException: Row not found or changed. at
    System.Data.Linq.ChangeProcessor.SubmitChanges(ConflictMode
    failureMode) at
    System.Data.Linq.DataContext.SubmitChanges(ConflictMode failureMode)
    at System.Data.Linq.DataContext.SubmitChanges() 

I&#39;ve had this problem for about a week, and no matter what I do, it is
still there, and the record doesn&#39;t get deleted.

Any ideas on what to do?

System.Data.Linq.ChangeConflictException: Row not found or changed

Say I have a very simple java object that only has some getXXX and setXXX properties.  This object is used only to handle values, basically a record or a type-safe (and performant) map.  I often need to covert this object to key value pairs (either strings or type safe) or convert from key value pairs to this object.

Other than reflection or manually writing code to do this conversion, what is the best way to achieve this?

An example might be sending this object over jms, without using the ObjectMessage type (or converting an incoming message to the right kind of object).


How to convert a Java object (bean) to key-value pairs (and vice versa)?

In Java, I have a `Set`, and I want to turn it into a sorted `List`.  Is there a method in the `java.util.Collections` package that will do this for me?

How do I sort a Set to a List in Java?

This may be a bit of an easy, headdesk sort of question, but my first attempt surprisingly completely failed to work.  I wanted to take an array of primitive longs and turn it into a list, which I attempted to do like this:

    long[] input = someAPI.getSomeLongs();
    List&lt;Long&gt; inputAsList = Arrays.asList(input); //Total failure to even compile!

What&#39;s the right way to do this?


Convert an array of primitive longs into a List of Longs

I&#39;m sure there&#39;s a good reason, but could someone please explain why the `java.util.Set` interface lacks `get(int Index)`, or any similar `get()` method?

It seems that sets are great for putting things into, but I can&#39;t find an elegant way of retrieving a single item from it.

If I know I want the first item, I can use `set.iterator().next()`, but otherwise it seems I have to cast to an Array to retrieve an item at a specific index?

What are the appropriate ways of retrieving data from a set? (other than using an iterator)

I&#39;m sure the fact that it&#39;s excluded from the API means there&#39;s a good reason for not doing this -- could someone please enlighten me?

**EDIT:**
Some extremely great answers here, and a few saying &quot;more context&quot;.  The specific scenario was a dbUnit test, where I could reasonably assert that the returned set from a query had only 1 item, and I was trying to access that item.

However, the question is more valid without the scenario, as it remains more focussed:

*What&#39;s the difference between set and list*.

Thanks to all for the fantastic answers below.

Why doesn&#39;t java.util.Set have get(int index)?

I&#39;m new to Mac/iPhone programming and Objective-C.  In C# and Java we have &quot;generics&quot;, collection classes whose members can only be of the type declared.  For example, in C# 

`Dictionary&lt;int, MyCustomObject&gt;`

can only contain keys that are integers and values that are of type MyCustomObject.  Does a similar mechanism exist in Objective-C?

Are there strongly-typed collections in Objective-C?

I&#39;m working on a little something and I am trying to figure out whether I can load an XDocument from a string. `XDocument.Load()` seems to take the string passed to it as a path to a physical XML file.

I want to try and bypass the step of first having to create the physical XML file and jump straight to populating the XDocument.

Any ideas?

Populate XDocument from String

Is there any way to have an XDocument print the xml version when using the ToString method? Have it output something like this:

&lt;pre&gt;&lt;code&gt;&amp;lt;?xml version=&quot;1.0&quot;?&amp;gt;
&amp;lt;!DOCTYPE ELMResponse [
]&amp;gt;
&amp;lt;Response&amp;gt;
&amp;lt;Error&amp;gt; ...&lt;/code&gt;&lt;/pre&gt;

I have the following:

&lt;pre&gt;&lt;code&gt;var xdoc = new XDocument(new XDocumentType(&quot;Response&quot;, null, null, &quot;\n&quot;), ...&lt;/code&gt;&lt;/pre&gt;

which will print this which is fine, but it is missing the &quot;&amp;lt;?xml version&quot; as stated above.

&lt;pre&gt;&lt;code&gt;&amp;lt;!DOCTYPE ELMResponse [
]&amp;gt;
&amp;lt;Response&amp;gt;
&amp;lt;Error&amp;gt; ...&lt;/code&gt;&lt;/pre&gt;

I know that you can do this by outputting it manually my self. Just wanted to know if it was possible by using XDocument.

How to print &lt;?xml version=&quot;1.0&quot;?&gt; using XDocument

Is there any way to get the xml encoding in the toString() Function?

**Example:**

    xml.Save(&quot;myfile.xml&quot;);

leads to

    &lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
    &lt;Cooperations&gt;
      &lt;Cooperation&gt;
        &lt;CooperationId&gt;xxx&lt;/CooperationId&gt;
        &lt;CooperationName&gt;Allianz Konzern&lt;/CooperationName&gt;
        &lt;LogicalCustomers&gt;

But 

    tb_output.Text = xml.toString();


leads to an output like this

    &lt;Cooperations&gt;
      &lt;Cooperation&gt;
        &lt;CooperationId&gt;xxx&lt;/CooperationId&gt;
        &lt;CooperationName&gt;Allianz Konzern&lt;/CooperationName&gt;
        &lt;LogicalCustomers&gt;
        ...

XDocument.ToString() drops XML Encoding Tag

It&#39;s a very simple problem that I have. I use XDocument to generate an XML file. I then want to return it as a XmlDocument class.
And I have an XmlDocument variable which I need to convert back to XDocument to append more nodes.

So, what is the *most efficient* method to convert XML between XDocument and XmlDocument? (Without using any temporary storage in a file.)

Converting XDocument to XmlDocument and vice versa

I am now learning [`XmlDocument`][1] but I&#39;ve just ran into [`XDocument`][2] and when I try to search the difference or benefits of them I can&#39;t find something useful, could you please tell me why you would use one over another ?


  [1]: http://msdn.microsoft.com/en-us/library/system.xml.xmldocument.aspx
  [2]: http://msdn.microsoft.com/en-us/library/system.xml.linq.xdocument.aspx

Content Type	Original Author	Original Content on Stackoverflow
Question	kitsune	View Question on Stackoverflow
Solution 1 - C#	Daniel Brückner	View Answer on Stackoverflow
Solution 2 - C#	ybo	View Answer on Stackoverflow
Solution 3 - C#	Mike_G	View Answer on Stackoverflow
Solution 4 - C#	bruno conde	View Answer on Stackoverflow

linq question: querying nested collections

C# Problem Overview

C# Solutions

Solution 1 - C#

Solution 2 - C#

Solution 3 - C#

Solution 4 - C#

Determine if NSNumber is NaN

c# - How to iterate through classes fields and set properties

Attributions