MongoDB学习笔记~关于官方驱动集成IQueryable之后的一些事

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关于官方驱动集成IQueryable之后的一些事，有好事也有坏事，好事就是它会将你的linq语句非常友好的翻译成MongoDB语句，而坏事就是有一些linq语句不会被翻译，不会被翻译的代价就是将整个结果集装到内存，然后进行linq to object的查询，效率自然是非常低的，呵呵。

好事

最新官方驱动中，添加了对IQueryable扩展方法的支持

        public static IMongoQueryable<TDocument> AsQueryable<TDocument>(this IMongoCollection<TDocument> collection);

1　它对Where完成支持

_webManageUsersRepository.GetModel().Where(i => i.LoginName == "zzl");

2　它对group完全支持

 var g = _webManageUsersRepository.GetModel()
                .GroupBy(i => i.DepartmentID, (i, v) => new
                {
                    dept = i,
                    userCount = v.Count()
                });

通过断点我们可以看到它所生成的mongodb语句，然后可以把语句放在命令行中去执行看看具体效果

db.WebManageUsers.aggregate([{ "$group" : { "_id" : "$DepartmentID", "userCount" : { "$sum" :  } } }])

上面写法是我比较喜欢的lambda表达式的方法，语法简介，漂亮，而我不太喜欢linq写法，但是，如果是多字段的分组，你就必须使用linq标准写法了，因为到目前为止，mongo官方驱动还不支持多字段分组的lambda写法，如下面的代码，分组结果就是错误的

 var bb = _webManageUsersRepository.GetModel()
                .GroupBy(
                i => new
                {
                    i.DepartmentID,
                    i.Status
                },
                (i, v) => new
                {
                    dept = i.DepartmentID,
                    status = i.Status,
                    userCount = v.Count()
                });

它不能正确的翻译成Mongo表达式

{aggregate([{ "$group" : { "dept" : "$DepartmentID", "status" : "$Status", "userCount" : { "$sum" :  }, "_id" :  } }])}

而使用传统的linq写法就可以被mongo驱动很好的翻译

  var gg = from a in _webManageUsersRepository.GetModel()
                     group a by new
                     {
                         dept = a.DepartmentID,
                         status = a.Status
                     } into g
                     select new RoleCount
                     {
                         dept = g.Key.dept,
                         status = g.Key.status,
                         userCount = g.Count()
                     };

下面生成的代码是正确的

aggregate([{ "$group" : { "_id" : { "dept" : "$DepartmentID", "status" : "$Status" }, "__agg0" : { "$sum" :  } } }, { "$project" : { "dept" : "$_id.dept", "status" : "$_id.status", "userCount" : "$__agg0", "_id" :  } }])}

可以在mongo客户端上看到正确的结果

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" 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坏事

对count()方法完成不支持，不推荐使用，如果要用到count()，建议使用mongo原生态的，而不是linq的

            Stopwatch sw1 = new Stopwatch();
            sw1.Restart();
            var a1 = _webManageUsersRepository.Count(i => true);//性能好
            sw1.Stop();
            var at1 = sw1.ElapsedMilliseconds;

            Stopwatch sw = new Stopwatch();
            sw.Restart();
            var a = _webManageUsersRepository.GetModel().Count();//性能差
            sw.Stop();
            var at = sw.ElapsedMilliseconds;

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