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);