MongoDB学习——用MongoDB的文档结构描述数据关系
MongoDB的集合（collection）可以看做关系型数据库的表，文档对象（document）可以看做关系型数据库的一条记录。但两者并不完全对等。表的结构是固定的，MongoDB集合并没有这个约束；另外，存入集合的文档对象甚至可以嵌入子文档，或者“子集合”。他们最终都可以用类似于BJSON的格式描述。我们今天就来分析MongoDB这一特性带来的独特数据管理方式。我们还是以samus驱动为例来分析，samus驱动支持两种方式访问数据库，基本方式和linq方式，基本方式在上篇以介绍过，linq方式我不想单独讲解应用实例，这篇我会用两种方式来对比介绍。一、包含子文档的集合操作
有这么一个应用场景，某网站提供会员登录的功能，用户需要注册账号才能享受会员服务，但是注册者可能会因为用户资料表单输入项过大而放弃填写，因此用户信息分为主要资料和详细资料两项，初次注册只需要填写主要资料就行了。我们打算把详细信息设计为子文档存储。
1. linq方式实现(1) 新建数据描述类，描述用户信息
[*]///
[*]/// 用户主要资料
[*]///
[*]public class UserInfo
[*]{
[*] public string UserId { get; set; }
[*] public string UserName { get; set; }
[*] public string PassWord { get; set; }
[*] public Detail Detail { get; set; }
[*]}
[*]
[*]///
[*]/// 用户详细资料
[*]///
[*]public class Detail
[*]{
[*] public string Address { get; set; }
[*] public int Age { get; set; }
[*] public string Email { get; set; }
[*]}
(2) 我们要新建一个用户业务操作类“UserBLL”。这个时候要让驱动知道UserInfo类描述了“用户资料”的字段信息，在GetMongo()方法实现了配置步骤，UserBLL完整代码如下：
[*]public class UserBLL
[*]{
[*] public string connectionString = "mongodb://localhost";
[*] public string databaseName = "myDatabase";
[*]
[*] private Mongo mongo;
[*] private MongoDatabase mongoDatabase;
[*]
[*] //注意这里泛型类型为“UserInfo”
[*] private MongoCollection mongoCollection;
[*]
[*] public UserBLL()
[*] {
[*] mongo = GetMongo();
[*] mongoDatabase = mongo.GetDatabase(databaseName) as MongoDatabase;
[*] mongoCollection = mongoDatabase.GetCollection() as MongoCollection;
[*] mongo.Connect();
[*] }
[*] ~UserBLL()
[*] {
[*] mongo.Disconnect();
[*] }
[*]
[*] ///
[*] /// 配置Mongo,将类UserInfo映射到集合
[*] ///
[*] private Mongo GetMongo()
[*] {
[*] var config = new MongoConfigurationBuilder();
[*] config.Mapping(mapping =>
[*] {
[*] mapping.DefaultProfile(profile =>
[*] {
[*] profile.SubClassesAre(t => t.IsSubclassOf(typeof(UserInfo)));
[*] });
[*] mapping.Map();
[*] });
[*] config.ConnectionString(connectionString);
[*] return new Mongo(config.BuildConfiguration());
[*] }
[*]}
(3) 接着，在“UserBLL”类中定义一个方法“InsertSomeData()”来插入一些数据：
[*]public void InsertSomeData()
[*]{
[*] UserInfo userInfo1 = new UserInfo()
[*] {
[*] UserId = "1001",
[*] UserName = "张三",
[*] PassWord = "123456"
[*] };
[*] mongoCollection.Save(userInfo1);
[*]
[*] UserInfo userInfo2 = new UserInfo()
[*] {
[*] UserId = "1002",
[*] UserName = "李四",
[*] PassWord = "123456",
[*] Detail = new Detail()
[*] {
[*] Address = "北京",
[*] Age = 20,
[*] Email = "lisi@163.com"
[*] }
[*] };
[*] mongoCollection.Save(userInfo2);
[*]
[*] UserInfo userInfo3 = new UserInfo()
[*] {
[*] UserId = "1003",
[*] UserName = "王五",
[*] PassWord = "123456",
[*] Detail = new Detail()
[*] {
[*] Address = "广东",
[*] Age = 20,
[*] Email = "wangwu@163.com"
[*] }
[*] };
[*] mongoCollection.Save(userInfo3);
[*]
[*] UserInfo userInfo4 = new UserInfo()
[*] {
[*] UserId = "1004",
[*] UserName = "赵六",
[*] PassWord = "123456",
[*] Detail = new Detail()
[*] {
[*] Address = "上海"
[*] }
[*] };
[*] mongoCollection.Save(userInfo4);
[*]
[*]}
(4) 定义一个查找数据的方法“Select”，它将查找用户详细信息中，地址在湖北的全部用户：
[*]///
[*]/// 查询详细资料地址为湖北的用户信息
[*]///
[*]public List Select()
[*]{
[*] return mongoCollection.Linq().Where(x => x.Detail.Address == "湖北").ToList();
[*]}
(5) 还定义一个删除数据的方法，将删除集合全部数据：
[*]///
[*]/// 删除全部用户信息
[*]///
[*]public void DeleteAll()
[*]{
[*] mongoCollection.Remove(x => true);
[*]}
(6) 在Main方法中添加如下代码：
[*]static void Main(string[] args)
[*]{
[*]
[*] UserBLL userBll = new UserBLL();
[*] userBll.InsertSomeData();
[*] var users = userBll.Select();
[*] foreach (var user in users)
[*] {
[*] Console.WriteLine(user.UserName + "是湖北人");
[*] };
[*] userBll.DeleteAll();
[*]}
(7) 打印如下信息：
[*]李四是北京人
[*]赵六是上海人
2. 普通实现
普通方式实现不想多讲，直接贴代码，看看与linq方式有什么区别：
[*]class Program
[*]{
[*] static void Main(string[] args)
[*] {
[*] UserBLL userBll = new UserBLL();
[*] userBll.InsertSomeData();
[*] var users = userBll.Select();
[*] foreach (var user in users)
[*] {
[*] Console.WriteLine(user["UserName"].ToString() + "是湖北人");
[*] };
[*] userBll.DeleteAll();
[*]
[*] Console.ReadLine();
[*] }
[*]}
[*]
[*]public class UserBLL
[*]{
[*] public string connectionString = "mongodb://localhost";
[*] public string databaseName = "myDatabase";
[*] public string collectionName = "UserInfo";
[*]
[*] private Mongo mongo;
[*] private MongoDatabase mongoDatabase;
[*] private MongoCollection mongoCollection;
[*]
[*] public UserBLL()
[*] {
[*] mongo = new Mongo(connectionString);
[*] mongoDatabase = mongo.GetDatabase(databaseName) as MongoDatabase;
[*] mongoCollection = mongoDatabase.GetCollection(collectionName) as MongoCollection;
[*] mongo.Connect();
[*] }
[*] ~UserBLL()
[*] {
[*] mongo.Disconnect();
[*] }
[*]
[*] ///
[*] /// 插入一些数据
[*] ///
[*] public void InsertSomeData()
[*] {
[*] Document userInfo1 = new Document();
[*] userInfo1["UserId"] = "1001";
[*] userInfo1["UserName"] = "张三";
[*] userInfo1["PassWord"] = "123456";
[*] mongoCollection.Save(userInfo1);
[*]
[*] Document userInfo2 = new Document();
[*] userInfo2["UserId"] = "1002";
[*] userInfo2["UserName"] = "李四";
[*] userInfo2["PassWord"] = "123456";
[*] //子文档
[*] var userInfo2Detail = new Document();
[*] userInfo2Detail["Address"] = "湖北";
[*] userInfo2Detail["Age"] = 20;
[*] userInfo2Detail["Email"] = "lisi@163.com";
[*] userInfo2["Detail"] = userInfo2Detail;
[*] mongoCollection.Save(userInfo2);
[*]
[*] Document userInfo3 = new Document();
[*] userInfo3["UserId"] = "1003";
[*] userInfo3["UserName"] = "王五";
[*] userInfo3["PassWord"] = "123456";
[*] var userInfo3Detail = new Document();
[*] userInfo3Detail["Address"] = "广东";
[*] userInfo3Detail["Age"] = 20;
[*] userInfo3Detail["Email"] = "wangwu@163.com";
[*] userInfo3["Detail"] = userInfo3Detail;
[*] mongoCollection.Save(userInfo3);
[*]
[*] Document userInfo4 = new Document();
[*] userInfo4["UserId"] = "1004";
[*] userInfo4["UserName"] = "赵六";
[*] userInfo4["PassWord"] = "123456";
[*] var userInfo4Detail = new Document();
[*] userInfo4Detail["Address"] = "湖北";
[*] userInfo4["Detail"] = userInfo4Detail;
[*] mongoCollection.Save(userInfo4);
[*]
[*] }
[*]
[*] ///
[*] /// 查询详细资料地址为湖北的用户信息
[*] ///
[*] public IEnumerable Select()
[*] {
[*] return mongoCollection.Find(new Document { { "Detail.Address", "湖北" } }).Documents;
[*] }
[*]
[*] ///
[*] /// 删除全部用户信息
[*] ///
[*] public void DeleteAll()
[*] {
[*] mongoCollection.Remove(new Document { });
[*] }
[*]
[*]}
最后，我们通过这段代码输出全部用户资料信息的BJSON格式：
[*]///
[*]/// 打印数据BJSON
[*]///
[*]public void PrintBJSON()
[*]{
[*] string BJSON = string.Empty;
[*] foreach (var documet in mongoCollection.FindAll().Documents)
[*] {
[*]
[*] BJSON += documet.ToString();
[*]
[*] }
[*] Console.WriteLine(BJSON);
[*]}
结果如下：
[*]{ "UserId": "1001", "UserName": "张三", "PassWord": "123456", "_id": "4d80ec1ab8a4731338000001" }
[*]{ "UserId": "1002", "UserName": "李四", "PassWord": "123456", "Detail": { "Address": "湖北", "Age": 20, "Email": "lisi@163.com" }, "_id": "4d80ec1ab8a4731338000002" }
[*]{ "UserId": "1003", "UserName": "王五", "PassWord": "123456", "Detail": { "Address": "广东", "Age": 20, "Email": "wangwu@163.com" }, "_id": "4d80ec1ab8a4731338000003" }
[*]{ "UserId": "1004", "UserName": "赵六", "PassWord": "123456", "Detail": { "Address": "湖北" }, "_id": "4d80ec1ab8a4731338000004" }
二、包含“子集合”的集合操作
同样举个例子：有一个学校人事管理系统要统计班级和学生的信息，现在定义了一个“班级集合”，这个集合里面的学生字段是一个“学生集合”，包含了本班全部学生。
1. linq方式实现
基础配置我就不多说了，数据类定义如下：
[*]///
[*]/// 班级信息
[*]///
[*]public class ClassInfo
[*]{
[*] public string ClassName { get; set; }
[*] public List Students { get; set; }
[*]}
[*]
[*]///
[*]/// 学生信息
[*]///
[*]public class Student
[*]{
[*] public string Name { get; set; }
[*] public int Age { get; set; }
[*]}
查询叫“张三”的学生在哪个班级，以及他的详细信息：(这里其实是ToList后在内存中查的,linq方式直接查询好像驱动不支持。)
[*]public List Select()
[*]{
[*] return mongoCollection.Linq().ToList().Where(x => x.Students.Exists(s => s.Name == "张三")).ToList();
[*]}
2. 普通实现
查询叫“张三”的学生在哪个班级，以及他的详细信息：
[*]public List Select()
[*]{
[*] var mongocollection = mongoDatabase.GetCollection("ClassInfo");
[*] return mongocollection.Find(new Document { { "Students.Name", "张三" } }).Documents.ToList();
[*]}
打印数据的BJSON：
[*]{ "_id": "4d814bae5c5f000000005f63", "ClassName": "1001", "Students": [ { "Name": "张三", "Age": 10 }, { "Name": "李四", "Age": 0 } ] }
[*]{ "_id": "4d814bae5c5f000000005f64", "ClassName": "1002", "Students": [ ] }
[*]{ "_id": "4d814bae5c5f000000005f65", "ClassName": "1003", "Students": [ { "Name": "王五", "Age": 11 }, { "Name": "赵六", "Age": 9 } ] }
MongoDB有它独特的文档结构可以描述数据对象之间的一些关系特征。它虽然没有关系型数据库多表符合查询那样强大的表间查询方式，但也可以通过文档结构描述更灵活的关系特性，可以这么说，关系型数据库能做的，MongoDB基本上也可以做到。甚至有些关系数据库不容易做到的，MongoDB也可以轻松做到，比如，描述数据类的继承关系等。
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