How to convert a ExpressionTree of form
Expression<Func<POCO1, bool>> exp = p => p.Age > 50;
to
Expression<Func<POCO2, bool>> exp2 = p => p.Age > 50;
where POCO1 and POCO2 are C# objects and both have Int32 Age property
How to convert a ExpressionTree of form
Expression<Func<POCO1, bool>> exp = p => p.Age > 50;
to
Expression<Func<POCO2, bool>> exp2 = p => p.Age > 50;
where POCO1 and POCO2 are C# objects and both have Int32 Age property
well, you can make custom expression visitor that will replace parameter references and patch member access expressions
class Converter<TTo>
{
class ConversionVisitor : ExpressionVisitor
{
private readonly ParameterExpression newParameter;
private readonly ParameterExpression oldParameter;
public ConversionVisitor(ParameterExpression newParameter, ParameterExpression oldParameter)
{
this.newParameter = newParameter;
this.oldParameter = oldParameter;
}
protected override Expression VisitParameter(ParameterExpression node)
{
return newParameter; // replace all old param references with new ones
}
protected override Expression VisitMember(MemberExpression node)
{
if (node.Expression != oldParameter) // if instance is not old parameter - do nothing
return base.VisitMember(node);
var newObj = Visit(node.Expression);
var newMember = newParameter.Type.GetMember(node.Member.Name).First();
return Expression.MakeMemberAccess(newObj, newMember);
}
}
public static Expression<Func<TTo, TR>> Convert<TFrom, TR>(
Expression<Func<TFrom, TR>> e
)
{
var oldParameter = e.Parameters[0];
var newParameter = Expression.Parameter(typeof(TTo), oldParameter.Name);
var converter = new ConversionVisitor(newParameter, oldParameter);
var newBody = converter.Visit(e.Body);
return Expression.Lambda<Func<TTo, TR>>(newBody, newParameter);
}
}
class A
{
public int Value { get; set; }
}
class B
{
public int Value { get; set; }
}
Expression<Func<A, int>> f = x => x.Value;
var f2 = Converter<B>.Convert(f);
Rough Steps:
Get the expression Cast it to BinaryExpression Get the left operand Cast it to MemberExpression Get the Underlying Type that the property belong to Change it to your new type if you can.
The type you get here is a property without setter as I guessed.
Expression<Func<MainWindow, bool >> exp1 = o => this.ActualHeight>50;
var type = ((MemberExpression)((BinaryExpression)exp1.Body).Left).Expression.Type;
So you must build a new expression
Here is the way
manually build linq expression for x => x.Child == itemToCompare.Child
Ideally - you don't. Make an interface that describes the Age property, and build the expression to refer to that. If you can't modify the POCO types, use a language like Go, where interfaces are implicit :-).