通过LINQ表达式树动态构建查询条件

public static class PredicateExtensions
    {
        public static Expression<Func<T, bool>> True<T>() { return f => true; }

        public static Expression<Func<T, bool>> False<T>() { return f => false; }

        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expression1, 
           Expression<Func<T, bool>> expression2)
        {
            var invokedExpression = Expression.Invoke(expression2, expression1.Parameters
                    .Cast<Expression>());

            return Expression.Lambda<Func<T, bool>>(Expression.Or(expression1.Body, invokedExpression),
            expression1.Parameters);
        }

        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expression1, 
              Expression<Func<T, bool>> expression2)
        {
            var invokedExpression = Expression.Invoke(expression2, expression1.Parameters
                 .Cast<Expression>());

            return Expression.Lambda<Func<T, bool>>(Expression.And(expression1.Body, 
                   invokedExpression), expression1.Parameters);
        }
    }

    public static class PredicateBuilder
    {

        public static Expression<Func<T, bool>> True<T>() { return f => true; }
        public static Expression<Func<T, bool>> False<T>() { return f => false; }
        public static Expression<T> Compose<T>(this Expression<T> first, Expression<T> second, Func<Expression, Expression, Expression> merge)
        {
            // build parameter 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 parameters from the first
            var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body);

            // apply composition of lambda expression bodies to parameters from the first expression 
            return Expression.Lambda<T>(merge(first.Body, secondBody), first.Parameters);
        }

        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
        {
            return first.Compose(second, Expression.And);
        }

        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
        {
            return first.Compose(second, Expression.Or);
        }
    }