MongoDB 系列(二) C# 内嵌元素操作 聚合使用

"_id" : "639d8a50-7864-458f-9a7d-b72647a3d226",
"ParentGuid" : "00000000-0000-0000-0000-000000000000",
"Name" : "汉字",
"Describe" : "",
"Enable" : true,
"Level" : 2,
"Subject" : "语文",
"Exams" : [
        {
            "ExamGuid" : "6635e1c6-2a22-404e-b58c-97ed9fc49ffc",
            "Grade" : "G2",
            "Questions" : [
                {
                    "_id" : "97eeeaaa-5902-4c11-bcdb-8b7a70485753"
                },
                {
                    "_id" : "628d5613-90b1-44fa-b02d-4074e86aa751"
                }
            ]
        },
        {
            "ExamGuid" : "b1e72692-6b63-4d98-a4bb-1b48765e7a96",
            "Grade" : "G1",
            "Questions" : [
                {
                    "_id" : "628d5613-90b1-44fa-b02d-4074e86aa751"
                }
            ]
        }
    ]

场景1：给内嵌集合的元素添加一个新的元素

1.首先根据筛选条件确定元素

  var filter = Builders<CustomKnowPoint>.Filter.And(
                          Builders<CustomKnowPoint>.Filter.Eq(o => o.Id, "639d8a50-7864-458f-9a7d-b72647a3d226"),
                          Builders<CustomKnowPoint>.Filter.Eq("Exams.ExamGuid", "6635e1c6-2a22-404e-b58c-97ed9fc49ffc"));

CustomKnowPoint为MongoDB映射的对象  Builders<CustomKnowPoint>.Filter.And 方法的参数是一个param[]数组,意思是将所有的过滤条件用And且的关系合并

var update = Builders<CustomKnowPoint>.Update.Push("Exams.$.Questions", new QuestionGuid(Guid.NewGuid().ToString()));

this.Collection.FindOneAndUpdate(filter, update);

2.执行后Questions内嵌集合就会在元素的末尾添加一条新的记录

场景2：内嵌集合的元素进行删除

过滤条件同上面的新增一样 通过对象本身的Id和内嵌元素的ExamGuid固定内嵌文档,移除文档的具体Filter对象是移除对象本身Builders<QuestionGuid>.Filter而不是Builders<CustomKnowPoint>.Filter

var update = Builders<CustomKnowPoint>.Update.PullFilter("Exams.$.Questions", Builders<QuestionGuid>.Filter.Eq("_id", "628d5613-90b1-44fa-b02d-4074e86aa751"));

this.Collection.FindOneAndUpdate(filter, update);

场景3：聚合使用

MongoDB的聚合管道将MongoDB文档在一个管道处理完毕后将结果传递给下一个管道处理。管道操作是可以重复的。表达式：处理输入文档并输出。表达式是无状态的，只能用于计算当前聚合管道的文档，不能处理其它的文档。

"_id" : "639d8a50-7864-458f-9a7d-b72647a3d226",
"ParentGuid" : "00000000-0000-0000-0000-000000000000",
"Name" : "汉字",
"Describe" : "",
"Enable" : true,
"Level" : ,
"Subject" : "语文",
"Exams" : [
        {
            "ExamGuid" : "6635e1c6-2a22-404e-b58c-97ed9fc49ffc",
            "Grade" : "G2",
            "Questions" : [
                {
                    "_id" : "97eeeaaa-5902-4c11-bcdb-8b7a70485753"
                },
                {
                    "_id" : "628d5613-90b1-44fa-b02d-4074e86aa751"
                }
            ]
        }
    ]

当我们只需要返回内嵌文档部分的时候 这种场景下我们就可以用到聚合来操作了 执行MongoDB语句

db.KnowPoint.aggregate(
[
    {
        /*此处$unwind：将文档中的某一个数组类型字段拆分成多条，每条包含数组中的一个值。*/
        $unwind : "$Exams"
    },
    { 
　　　　/*此处$match ：过滤文档筛选条件。*/
        $match :
            {
                "Exams.ExamGuid" : "6635e1c6-2a22-404e-b58c-97ed9fc49ffc"
             }
     },
     { 
　　　　/*此处group 分组。*/
         $group :
            {
                _id :
                { 
　　　　　　　　　　　　/*此处按照各种属性拼凑分组 将各属性组成一个Id的属性*/
                    "_id" : "$_id", "ParentGuid" : "$ParentGuid", "Name" : "$Name", "Enable" : "$Enable", "Level" : "$Level", "Subject" : "$Subject"
                 },
                 "Exams" :
                 { 
　　　　　　　　　　　　/*此处push将之前分组的Exams再写进去*/
                     "$push" : "$Exams"
                 }
              }
       }
 ])

相应的C# 驱动程序

            List<string> keys = new List<string>() { "_id", "ParentGuid", "Name", "Enable", "Level", "Subject" };
            var stages = new List<IPipelineStageDefinition>();
            #region 过滤条件
            stages.Add(new JsonPipelineStageDefinition<BsonDocument, BsonDocument>
               (
                   "{" +
                            "$unwind:\"$Exams\"" +
                   "}"
               ));
            stages.Add(new JsonPipelineStageDefinition<BsonDocument, BsonDocument>
                (
                    "{" +
                            "$match:" +
                            "{" +
                                    "\"Exams.ExamGuid\":" +
                                    "{" +
                                                "$in:" + JsonConvert.SerializeObject(new List<string>() { "6635e1c6-2a22-404e-b58c-97ed9fc49ffc"}) +
                                    "}" +
                            "}" +
                    "}"
                ));

            stages.Add(new JsonPipelineStageDefinition<BsonDocument, BsonDocument>
                (
                    "{" +
                             "$group:" +
                                         "{" +
                                                    "_id:{ " + string.Join(",", keys.Select(o => "\"" + o + "\":\"$" + o + "\"").ToList()) + "  }," +
                                                    "Exams:{$push:\"$Exams\"}" +
                                         "}" +
                    "}"
                ));
            #endregion

            var pipeline = new PipelineStagePipelineDefinition<BsonDocument, BsonDocument>(stages);

            var result = this.Context
                                      .DbSet<BsonDocument>(nameof(KnowPoint))
                                      .Aggregate(pipeline)
                                      .ToList()