记录一次使用 Expression 的方法

　　　　　/// <summary>
        /// 实现 Name == "a" or Name == "b" or Name == "c"
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="query"></param>
        /// <param name="condition"></param>
        /// <param name="selector"></param>
        /// <param name="values"></param>
        /// <returns></returns>
        public static IQueryable<T> WhereIfEqOr<T, TResult>(this IQueryable<T> query, bool condition, Expression<Func<T, TResult>> selector, List<TResult> values)
        {
            if (condition == false) return query;
            if (values != null && values.Count > 0)
            {
                Type type = typeof(T);
                ParameterExpression paramExp = Expression.Parameter(type, "x");
                var memberExp = selector.Body as MemberExpression;
                Expression propertyExp = Expression.Property(paramExp, memberExp.Member.Name);
                Expression expression = Expression.Equal(propertyExp, Expression.Constant(values[0], typeof(TResult)));
                for (int i = 1; i < values.Count; i++)
                {
                    expression = Expression.Or(expression, Expression.Equal(propertyExp, Expression.Constant(values[i], typeof(TResult))));
                }
                var lambda = Expression.Lambda<Func<T, bool>>(expression, paramExp);
                query = query.Where(lambda);
            }
            return query;
        }

　　　　　/// <summary>
        /// 实现 Name like "%a%" or Name like "%b%" or Name like "%c%"
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="query"></param>
        /// <param name="condition"></param>
        /// <param name="selector"></param>
        /// <param name="values"></param>
        /// <returns></returns>
        public static IQueryable<T> WhereIfContainsOr<T, TResult>(this IQueryable<T> query, bool condition, Expression<Func<T, TResult>> selector, List<TResult> values)
        {
            if (condition == false) return query;
            if (values != null && values.Count > 0)
            {
                Type type = typeof(T);
                ParameterExpression paramExp = Expression.Parameter(type, "x");
                var memberExp = selector.Body as MemberExpression;
                Expression propertyExp = Expression.Property(paramExp, memberExp.Member.Name);
                Expression expression = Expression.Call(propertyExp, typeof(string).GetMethod("Contains", new Type[] { typeof(string) }), Expression.Constant(values[0], typeof(TResult)));
                for (int i = 1; i < values.Count; i++)
                {
                    expression = Expression.Or(expression, Expression.Call(propertyExp, typeof(string).GetMethod("Contains", new Type[] { typeof(string) }), Expression.Constant(values[i], typeof(TResult))));
                }
                var lambda = Expression.Lambda<Func<T, bool>>(expression, paramExp);
                query = query.Where(lambda);
            }
            return query;
        }

这两种方法可以使用一个字段的或关系