Added support for SQL length string function. Closes #25.

Added support for SQL Server, MySQL and Access regarding the length string function.

DatabaseObjects.vbproj

@@ -194,6 +194,7 @@
     <Compile Include="SQL\Expressions\SQLFunctionExpression.vb" />
     <Compile Include="SQL\Expressions\SQLGetDateFunctionExpression.vb" />
     <Compile Include="SQL\Expressions\SQLLeftExpression.vb" />
+    <Compile Include="SQL\Expressions\SQLLengthFunctionExpression.vb" />
     <Compile Include="SQL\Select\SQLSelectHavingCondition.vb" />
     <Compile Include="SQL\Select\SQLSelectHavingConditions.vb" />
     <Compile Include="SQL\Select\SQLConditionExpression.vb" />

SQL/Expressions/SQLFunctionExpression.vb

@@ -38,11 +38,38 @@ Namespace SQL
         Public Sub New(strFunctionName As String, ParamArray arguments() As SQLExpression)
 
             Me.New(strFunctionName)
+            InitializeArguments(arguments)
+
+        End Sub
+
+        ''' <summary>
+        ''' Used when the arguments are known but the function name is dependant on the connection type.
+        ''' Typically, in this scenario the FunctionName() will be overridden.
+        ''' </summary>
+        ''' <param name="arguments"></param>
+        ''' <remarks></remarks>
+        Protected Sub New(ParamArray arguments() As SQLExpression)
+
+            InitializeArguments(arguments)
+
+        End Sub
+
+        Private Sub InitializeArguments(ParamArray arguments() As SQLExpression)
+
+            If arguments.Any(Function(item) item Is Nothing) Then
+                Throw New ArgumentNullException
+            End If
 
             pobjFunctionArguments = arguments
 
         End Sub
 
+        Protected Overridable Function FunctionName(ByVal eConnectionType As Database.ConnectionType) As String
+
+            Return pstrFunctionName
+
+        End Function
+
         Friend Overrides Function SQL(ByVal eConnectionType As Database.ConnectionType) As String
 
             Dim strArguments As String = String.Empty
@@ -51,7 +78,7 @@ Namespace SQL
                 strArguments = String.Join(", ", pobjFunctionArguments.Select(Function(argument) argument.SQL(eConnectionType)).ToArray)
             End If
 
-            Return pstrFunctionName & "(" & strArguments & ")"
+            Return Me.FunctionName(eConnectionType) & "(" & strArguments & ")"
 
         End Function
 

SQL/Expressions/SQLLengthFunctionExpression.vb

@@ -0,0 +1,43 @@
+
+' ___________________________________________________
+'
+'  © Hi-Integrity Systems 2012. All rights reserved.
+'  www.hisystems.com.au - Toby Wicks
+' ___________________________________________________
+'
+
+Option Strict On
+Option Explicit On
+
+Namespace SQL
+
+    ''' <summary>
+    ''' SQL function that returns the length of a string.
+    ''' </summary>
+    Public Class SQLLengthFunctionExpression
+        Inherits SQLFunctionExpression
+
+        Public Sub New(objExpression As SQLExpression)
+
+            MyBase.New(objExpression)
+
+        End Sub
+
+        Protected Overrides Function FunctionName(ByVal eConnectionType As Database.ConnectionType) As String
+
+            Select Case eConnectionType
+                Case Database.ConnectionType.MySQL
+                    Return "LENGTH"
+                Case Database.ConnectionType.SQLServer, Database.ConnectionType.MicrosoftAccess
+                    Return "LEN"
+                Case Else
+                    Throw New NotImplementedException(eConnectionType.ToString)
+            End Select
+
+            Return MyBase.FunctionName(eConnectionType)
+
+        End Function
+
+    End Class
+
+End Namespace