How to create and Expression tree to do the same as "StartsWith"

Posted by Jonathan on Stack Overflow See other posts from Stack Overflow or by Jonathan
Published on 2010-12-29T11:51:29Z Indexed on 2010/12/29 11:53 UTC
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Hi to all.

Currently, I have this method to compare two numbers

Private Function ETForGreaterThan(ByVal query As IQueryable(Of T), ByVal propertyValue As Object, ByVal propertyInfo As PropertyInfo) As IQueryable(Of T)

    Dim e As ParameterExpression = Expression.Parameter(GetType(T), "e")
    Dim m As MemberExpression = Expression.MakeMemberAccess(e, propertyInfo)
    Dim c As ConstantExpression = Expression.Constant(propertyValue, propertyValue.GetType())
    Dim b As BinaryExpression = Expression.GreaterThan(m, c)
    Dim lambda As Expression(Of Func(Of T, Boolean)) = Expression.Lambda(Of Func(Of T, Boolean))(b, e)
    Return query.Where(lambda)

End Function

It works fine and is consumed in this way

query = ETForGreaterThan(query, Value, propertyInfo)

As you can see, I give it an IQueryable collection and it add a where clause to it, base on a property and a value. Y can construct Lessthan, LessOrEqualThan etc equivalents as Expression has this operators predefined.

¿How can I transform this code to do the same with strings? Expression don't give me a predefined operator like "contains" or "startwith" and I'm really noob with Expression trees.

Thanks, and please Post your answer in C#/VB. Choose the one that make you feel more confortable.

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