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copied!<p>You have to analyze the parameters and the body of the LambdaExpression and build a new one. You can access the body it using <code>predicate.Body</code> and the parameters using predicate.Parameters. The new expression has a parameter of type UserBO instead of UserDataObject. In addition, the ParameterExpression(s) in the body must use the new parameter.<br/> Of course, this assumes that it is a simple scenario where the BO and the DataObject have the same properties. More complex transformations are possible but need a deeper analysis of the expression tree.<br/> In order to vive you a starting Point, I out together a sample with a very similar BusinessObject and DataObject. The key component is a class derived from ExpressionVisitor that performs the conversion:</p> <pre><code>using System; using System.Collections.Generic; using System.Linq; using System.Linq.Expressions; using System.Text; namespace ConvertExpression { public class BusinessObject { public int Value { get; set; } } public class DataObject { public int Value { get; set; } } internal class ExpressionConverter : ExpressionVisitor { public Expression Convert(Expression expr) { return Visit(expr); } private ParameterExpression replaceParam; protected override Expression VisitLambda<T>(Expression<T> node) { if (typeof(T) == typeof(Func<BusinessObject, bool>)) { replaceParam = Expression.Parameter(typeof(DataObject), "p"); return Expression.Lambda<Func<DataObject, bool>>(Visit(node.Body), replaceParam); } return base.VisitLambda<T>(node); } protected override Expression VisitParameter(ParameterExpression node) { if (node.Type == typeof(BusinessObject)) return replaceParam; // Expression.Parameter(typeof(DataObject), "p"); return base.VisitParameter(node); } protected override Expression VisitMember(MemberExpression node) { if (node.Member.DeclaringType == typeof(BusinessObject)) { var member = typeof(DataObject).GetMember(node.Member.Name, System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.Instance).FirstOrDefault(); if (member == null) throw new InvalidOperationException("Cannot identify corresponding member of DataObject"); return Expression.MakeMemberAccess(Visit(node.Expression), member); } return base.VisitMember(node); } } public class ConvertExpression { public static void Main() { BusinessObject[] bos = { new BusinessObject() { Value = 123 }, new BusinessObject() { Value = 246 } }; DataObject[] dos = { new DataObject() { Value = 123 }, new DataObject() { Value = 246 } }; Expression<Func<BusinessObject, bool>> boExpr = x => x.Value == 123; var conv = new ExpressionConverter(); Expression<Func<DataObject, bool>> doExpr = (Expression<Func<DataObject, bool>>) conv.Convert(boExpr); var selBos = bos.Where(boExpr.Compile()); Console.WriteLine("Matching BusinessObjects: {0}", selBos.Count()); foreach (var bo in selBos) Console.WriteLine(bo.Value); var compDoExpr = doExpr.Compile(); var selDos = dos.Where(doExpr.Compile()); Console.WriteLine("Matching DataObjects: {0}", selDos.Count()); foreach (var dataObj in selDos) Console.WriteLine(dataObj.Value); Console.ReadLine(); } } } </code></pre>

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