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POVB.NET 2010 and MySql - handling DB NULLs for lazy people
 

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  1. POVB.NET 2010 and MySql - handling DB NULLs for lazy people
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    <p>I want to initialize a class with data coming from a MySql db. Some fields can be null:</p> <pre><code>Dim dr As MySqlDataReader = ... Dim item As New Item(dr.GetInt16(0), dr.GetString(1), dr.GetString(2)) </code></pre> <p>Suppose the last two fields could be NULL In the db, so that calling GetString on that field causes an exception. </p> <p>I could certainly write code to test for NULLs before I get each field:</p> <pre><code>dim field1 as String if ( dr.IsDbNull(1) ) field1 = Nothing ' or even "" else field1 = dr.GetString(1) </code></pre> <p>But if you have many fields this is an "ifs" nightmare. </p> <p>To this purpose I rewrote the IIf VB function to make it more typed, thus to avoid casts:</p> <pre><code>Namespace Util Public Shared Function IIf(Of T)(ByVal condition As Boolean, ByVal iftrue As T, ByVal iffalse As T) As T If condition Then Return iftrue Else Return iffalse End Function </code></pre> <p>So that I could write something like:</p> <pre><code>Dim item As New Item( dr.GetInt16(0), Util.IIf(dr.IsDbNull(1), "", dr.GetString(1), Util.IIf(dr.IsDbNull(2), "", dr.GetString(2)) </code></pre> <p>The typed <strong>IIf</strong> works well in other cases, but unfortunately it doesn't in this instance, because <strong>being it a normal function and not a language keyword</strong>, each inpout parameter is evaluated during the call, and when the field is NULL the exception is raised. </p> <p>Can you think of an elegant if-less solution?</p>
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