var comment = conn.QuerySet<Comment>()
                     .Where(x => x.Id.NotIn(new int[] { 1, 2, 3 }) 
                     && x.SubTime.AddMinutes(50) < DateTime.Now.AddDays(-1) 
                     && x.Type.IsNotNull())
                     .ToList();　

 var comment = conn.QuerySet<Comment>()
                    .From<Comment, News, ResourceMapping>()
                    .Where((a, b, c) => a.Id == 1 
                    && b.Headlines.IsNotNull() 
                    && c.RSize > 100);

var comment = conn.QuerySet<Comment>()
                    .From<Comment, News, ResourceMapping>()
                    .Where((a, b, c) => a.Id == 1 
                    && b.Headlines.IsNotNull() 
                    && c.RSize > 100)
                    .GetQuerySet()
                    .ToList();

    /// <summary>
    /// 定义一个四表联合扩展类
    /// </summary>
    /// <typeparam name="T">对应QuerySet的泛型</typeparam>
    /// <typeparam name="T1">扩展泛型1</typeparam>
    /// <typeparam name="T2">扩展泛型2</typeparam>
    /// <typeparam name="T3">扩展泛型3</typeparam>
    /// <typeparam name="T4">扩展泛型4</typeparam>
    public class testFrom<T, T1, T2, T3,T4> : ISelect<T>
    {
        public testFrom(QuerySet<T> querySet) : base(querySet)
        {
 
        }
        //定义了一个Where
        public testFrom<T, T1, T2, T3,T4> Where(Expression<Func<T1, T2, T3,T4, bool>> select)
        {
            base.Where(select);
            return this;
        }
        //定义了一个ToList
        public IEnumerable<TReturn> ToList<TReturn>(Expression<Func<T1, T2, T3,T4, TReturn>> select)
        {
            return base.ToList<TReturn>(select);
        }
    }

                //首先声明一个QuerySet
                var querySet = conn.QuerySet<Comment>();
                /*把定义的querySet实例带入到扩展类中
              （注意：第一个T类型必须对应querySet的泛型，如Comment）*/
                var list = new testFrom<Comment, Comment, News, ResourceMapping, LikeRecord>(querySet)
                    .Where((a, b, c, d) => a.Id == 1 
                    && b.NewsLabel.Contains("t"))
                    .GetQuerySet()
                    .ToList();

public class ISelect<T>
    {
        public ISelect(QuerySet<T> querySet);
 
        public TReturn Get<TReturn>(LambdaExpression exp);
        public QuerySet<T> GetQuerySet();
        public ISelect<T> OrderBy<TProperty>(Expression<Func<TProperty, object>> field);
        public ISelect<T> OrderByDescing<TProperty>(Expression<Func<TProperty, object>> field);
        public PageList<TReturn> PageList<TReturn>(int pageIndex, int pageSize, LambdaExpression exp);
        public IEnumerable<TReturn> ToList<TReturn>(LambdaExpression exp);
        public QuerySet<T> Where(LambdaExpression exp);
    }

  var comment = conn.QuerySet<Comment>()
                    .Where(x => x.Content == "test1" && x.Content.Contains("t"))
                    .Get(x => new
                    {
                        Id = 123,
                        ArticleId = x.ArticleId
                    });

var comment = conn.QuerySet<Comment>()
                    .Join<Comment, News>((a, b) => a.ArticleId == b.Id)
                    .Where(x => x.Content == "test1" && x.Content.Contains("t"))
                    .Where<Comment, News>((a, b) => a.SubTime < DateTime.Now.AddDays(-5) && a.Id > a.Id % 1)
                    .Get(x => new
                    {
                        count = Convert.ToInt32("(select count(1) from Comment_4)"),
                        aaa = "6666",
                    });

var comment = conn.QuerySet<Comment>()
                     .Join<Comment, News>((a, b) => a.ArticleId == b.Id)
                     .Join<Comment, ResourceMapping>((a, b) => a.Id == b.FKId)
                     .Where(x => x.Content == "test")
                     .From<Comment, News, ResourceMapping>()
                     .OrderBy<News>(x => x.Id)
                     .Where((a, b, c) => a.ArticleId == b.Id)
                     .PageList(1, 10, (a, b, c) => new
                     {
                         id = a.Id,
                         name = b.NewsLabel,
                         resource = c.RPath,
                         rownum = Convert.ToInt32("ROW_NUMBER() OVER(ORDER BY Comment.Id)"),
                         NewsLable = "News.NewsLabel"
                     });

var comment1 = conn.QuerySet<Comment>()
                    .Join<Comment, News>((a, b) => a.ArticleId == b.Id)
                    .Where(x => x.Id.Between(80, 100) 
                    && x.SubTime.AddDays(-10) < DateTime.Now && x.Id > 10)
                    .From<Comment, News>()
                    .Get((a, b) => new
                    {
                        //(不查询数据库的方法可以任意使用)
                        test = new List<int>() { 3, 3, 1 }.FirstOrDefault(y => y == 1),
                        aaa = "6666" + "777",
                        Content = a.Content + "'test'" + b.Headlines + a.IdentityId,
                        //此字段会拼接成子查询，不用担心循环查询造成的性能问题
                        bbb = new QuerySet<Comment>(conn, new MySqlProvider())
                              .Where(y => y.ArticleId == b.Id && y.Content.Contains("test")).Sum<Comment>(x => x.Id),
                        ccc = a.IdentityId,
                        ddd = Convert.ToInt32("(select count(1) from Comment)")
                    });