Workaround for https://www.re-motion.org/jira/browse/RMLNQSQL-54

[Toni Wenzel]

Hi There,

is there any workaround for the https://www.re-motion.org/jira/browse/RMLNQSQL-54 bug? I mean, is there any option that I can write a transformer or subclass any visitor in order to fix this issue?

[Michael Ketting]

Hi Toni!

Without looking up particular extension points: Since the issue is the ?: operator, you should be able to write a visitor which detects the ConditionalExpression and return this as a the &&, || combination from the issue's comment.

Let me know if that helps :)

Best regards, Michael

[Toni Wenzel]

Thanks a lot.

I've created following transformer and added it to the ExpressionTransformerRegistry.

Imports System.Linq.Expressions

Imports System.Reflection

Imports Remotion.Linq.Clauses.Expressions

Imports Remotion.Linq.Parsing.ExpressionVisitors.Transformation

''' <summary>

''' Transforms IIF expressions to ((&lt;cond1&gt; &amp;&amp; &lt;cond2&gt;) || &lt;cond3&gt;) due to https://www.re-motion.org/jira/browse/RMLNQSQL-54

''' </summary>

''' <seealso cref="Remotion.Linq.Parsing.ExpressionVisitors.Transformation.IExpressionTransformer(Of ConditionalExpression)" />

Friend Class IIFTransformer

Implements IExpressionTransformer(Of ConditionalExpression)

''' <summary>

''' Transforms a given <see cref="T:System.Linq.Expressions.Expression" />.

''' </summary>

''' <param name="expression">The expression to be transformed.</param>

''' <returns>

''' The result of the transformation, or <paramref name="expression" /> if no transformation was applied.

''' </returns>

Public Function Transform(expression As ConditionalExpression) As Expression Implements IExpressionTransformer(Of ConditionalExpression).Transform

ArgumentUtility.CheckNotNull(NameOf(expression), expression)

If (expression.Test.Type = TYPE_BOOL AndAlso expression.IfTrue.Type = TYPE_BOOL) Then

' as described in https://www.re-motion.org/jira/browse/RMLNQSQL-54

' we should rewrite the  <cond1> ? <cond2> : <cond3>

' to ((<cond1> && <cond2>) || <cond3>).

Dim condition1 As Expression = expression.Test

Dim condition2 As Expression = expression.IfTrue

Dim condition3 As Expression = expression.IfFalse

Dim first As Expression = Expressions.Expression.MakeBinary(ExpressionType.AndAlso, condition1, condition2)

Return Expressions.Expression.MakeBinary(ExpressionType.OrElse, first, condition3)

Else

Return expression

End If

End Function

''' <summary>

''' Gets the expression types supported by this <see cref="IIFTransformer" />.

''' </summary>

''' <value>

''' The supported expression types.

''' </value>

Public ReadOnly Property SupportedExpressionTypes As ExpressionType() Implements IExpressionTransformer(Of ConditionalExpression).SupportedExpressionTypes

Get

Return {ExpressionType.Conditional}

End Get

End Property

End Class

Everything is working fine, so far. Any thoughts on the code?

Regards

Toni

[Michael Ketting]

Hi Toni!

Glad it works! I think the code's just fine / would have written something that looks just like it :)

Best regards, Michael

[Toni Wenzel]

Thanks.

I'm currently running in a issue where the condition2 and condition3 are of type nullable<boolean>.

if condition1 is bool the MakeBinary fails because the two types can't be compared.

Any idea how I can manage that?

[Michael Ketting]

Hmm... I think you could just throw a ConvertExpression at it. Casts to nullable types are transparent for SQL, it will just compare VALUE with NULL and result in FALSE.