May 2009 Entries

LINQ to XML -How to use XPass for elements selection

I am just starting to work with LINQ to XML and tried to find child document similar to the following: xml.Element("client/child"); But it throw exception System.Xml.XmlException: The '/' character, hexadecimal value 0x2F, cannot be included in a name. The reason is that LINQ to XML doesn't directly support XPAth Fortunately there are extensions, that allow to use XPath for XElement search/selection. using System.Xml.XPath; and then var clients = xml.XPathSelectElements ( "client/child" ); Consider, ......

Misleading error message when NullReferenceException thrown within Comparer

We've got an error messgae from custom comparer: IComparer (or the IComparable methods it relies upon) did not return zero when Array.Sort called x. CompareTo(x). After investigation it was found, that the error was caused by NullReferenceException, thrown within Comparer. I've suggested to Microsoft , that the actual NullReferenceException error message should be shown instead of this misleading one. See also similar feedback https://connect.microsoft.c... ......

EnsureDirectoryExists helper function

Below is a simple EnsureDirectoryExists helper function: public static void EnsureDirectoryExists(string targetPath) { string dir = Path.GetDirectoryName(targe... if (!Directory.Exists(dir)) { Directory.CreateDirectory(d... } } ......

Use HashSet instead of "seen" Hashtable.

In our code (originally created in .Net 1.1) there are a few examples of "seen" Hashtable pattern Hashtable seen = new Hashtable(); for (int i = 0; i < nCount; i++) { if (seen[key] == null) { //Do the changes seen.Add(key, key); } } It's better to use type-safe HashSet: HashSet<string> seen = new HashSet<string>(); for (int i = 0; i < nCount; i++) { if (!seen.Contains(key)) { //Do the changes seen.Add(key); } } ......

Don't Repeat Yourself(DRY principle) when modifying existing function

If there is an existing non-trivial function and you need to change it , do NOT copy and paste it , but modify to satisfy new requirements. You may be need to split a big function into small ones and call them in different order or with different parameters. Often you need just to add extra parameter to the function and have if-else branches depending on a new parameter. In some cases new change is actually a fix of the problem, that applicable to all usages of the function. Remember that "Copy and ......

Typed DataTable's base class in VS008

I have a typed Dataset, generated by VS Designer. Resently I've added a new column to one of the tables, and suddently in different DLLs where the dataset was used, I've started to get Error 22 The type 'System.Data.TypedTableBase... is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Data.DataSetExtensi... Version=3.5.0.0, Culture=neutral, PublicKeyToken=b77a5c561934... Apparently VS 2008 changed the base class for Typed DataTables 3.5 : public ......

Safe Save DateTime to SQL Database.

When I tried to save DateTime data to SQL database, I've got SqlDateTime overflow. Must be between 1/1/1753 12:00:00 AM and 12/31/9999 11:59:59 PM. The problem is described in http://blogs.vertigosoftwar... I've had to create a function object SafeSqlDateTime(DateTime dtValue) { object theValue = dtValue; if (dtValue <(DateTime) SqlDateTime.MinValue) // January 1, 1753. { theValue = null; } return theValue; } For opposite SqlDateTime to DateTime Conversion ......

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