Expression与Func学习



 Expression用于实现动态的查询语句

例子：

int[] intlist = { 1, 3, 5, 7, 9 };
            List<int> result = new List<int>();
            Expression<Func<int, string>> me = a => a.ToString();
            //MessageBox.Show(me.Compile()(66));
            Expression<Func<int, bool>> exp0 = a => a>5 ;
            Expression<Func<int, bool>> exp1 = b => b<9;
          //  Expression<Func<int, int>> temp= PredicateBuilder.Or<int>(t0,t1);
            Expression<Func<int, bool>> temp1=exp0.And(exp1);
             Func < int, bool> kk = exp0.And(exp1).Compile();
               result = intlist.Where(exp0.And(exp1).Compile()).ToList();

  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<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr1,
                                                            Expression<Func<T, bool>> expr2)
        {
            var invokedExpr = System.Linq.Expressions.Expression.Invoke(expr2, expr1.Parameters.Cast<System.Linq.Expressions.Expression>());
            return Expression.Lambda<Func<T, bool>>
                  (Expression.OrElse(expr1.Body, invokedExpr), expr1.Parameters);
        }

        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expr1,
                                                             Expression<Func<T, bool>> expr2)
        {
            var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
            return Expression.Lambda<Func<T, bool>>
                  (Expression.AndAlso(expr1.Body, invokedExpr), expr1.Parameters);
        }
    }