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copied!<p>Please find the solution in the blog post below:</p> <p><a href="http://petemontgomery.wordpress.com/2011/02/10/a-universal-predicatebuilder/" rel="nofollow">A universal PredicateBuilder</a></p> <p>The author of this blog post provide another to implementation of "Add" method to combine 2 expression.</p> <pre><code>/// <summary> /// Enables the efficient, dynamic composition of query predicates. /// </summary> public static class PredicateBuilder { /// <summary> /// Creates a predicate that evaluates to true. /// </summary> public static Expression<Func<T, bool>> True<T>() { return param => true; } /// <summary> /// Creates a predicate that evaluates to false. /// </summary> public static Expression<Func<T, bool>> False<T>() { return param => false; } /// <summary> /// Creates a predicate expression from the specified lambda expression. /// </summary> public static Expression<Func<T, bool>> Create<T>(Expression<Func<T, bool>> predicate) { return predicate; } /// <summary> /// Combines the first predicate with the second using the logical "and". /// </summary> public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second) { return first.Compose(second, Expression.AndAlso); } /// <summary> /// Combines the first predicate with the second using the logical "or". /// </summary> public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second) { return first.Compose(second, Expression.OrElse); } /// <summary> /// Negates the predicate. /// </summary> public static Expression<Func<T, bool>> Not<T>(this Expression<Func<T, bool>> expression) { var negated = Expression.Not(expression.Body); return Expression.Lambda<Func<T, bool>>(negated, expression.Parameters); } /// <summary> /// Combines the first expression with the second using the specified merge function. /// </summary> static Expression<T> Compose<T>(this Expression<T> first, Expression<T> second, Func<Expression, Expression, Expression> merge) { // zip parameters (map from parameters of second to parameters of first) var map = first.Parameters .Select((f, i) => new { f, s = second.Parameters[i] }) .ToDictionary(p => p.s, p => p.f); // replace parameters in the second lambda expression with the parameters in the first var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body); // create a merged lambda expression with parameters from the first expression return Expression.Lambda<T>(merge(first.Body, secondBody), first.Parameters); } class ParameterRebinder : ExpressionVisitor { readonly Dictionary<ParameterExpression, ParameterExpression> map; ParameterRebinder(Dictionary<ParameterExpression, ParameterExpression> map) { this.map = map ?? new Dictionary<ParameterExpression, ParameterExpression>(); } public static Expression ReplaceParameters(Dictionary<ParameterExpression, ParameterExpression> map, Expression exp) { return new ParameterRebinder(map).Visit(exp); } protected override Expression VisitParameter(ParameterExpression p) { ParameterExpression replacement; if (map.TryGetValue(p, out replacement)) { p = replacement; } return base.VisitParameter(p); } } } </code></pre>

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