MongoDB的3.x版本Java驱动相对2.x做了全新的设计，类库和使用方法上有很大区别。例如用Document替换BasicDBObject、通过Builders类构建Bson替代直接输入$命令等，本文整理了基于3.2版本的常用增删改查操作的使用方法。为了避免冗长的篇幅，分为增删改、查询、聚合、地理索引等几部分。

先看用于演示的类的基本代码

import static com.mongodb.client.model.Filters.*;
import static com.mongodb.client.model.Projections.*;
import static com.mongodb.client.model.Sorts.*;import java.text.ParseException;
import java.util.Arrays;import org.bson.BsonType;
import org.bson.Document;import com.mongodb.Block;
import com.mongodb.MongoClient;
import com.mongodb.client.FindIterable;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import com.mongodb.client.model.Filters;
import com.mongodb.client.model.Projections;public class FindExamples {public static void main(String[] args) throws ParseException {//根据实际环境修改ip和端口MongoClient mongoClient = new MongoClient("localhost", 27017);MongoDatabase database = mongoClient.getDatabase("lesson");FindExamples client = new FindExamples(database);client.show();mongoClient.close();}private MongoDatabase database;public FindExamples(MongoDatabase database) {this.database = database;}public void show() {MongoCollection<Document> mc = database.getCollection("blog");//每次执行前清空集合以方便重复运行mc.drop();//插入用于测试的文档Document doc1 = new Document("title", "good day").append("owner", "tom").append("words", 300).append("comments", Arrays.asList(new Document("author", "joe").append("score", 3).append("comment", "good"), new Document("author", "white").append("score", 1).append("comment", "oh no")));Document doc2 = new Document("title", "good").append("owner", "john").append("words", 400).append("comments", Arrays.asList(new Document("author", "william").append("score", 4).append("comment", "good"), new Document("author", "white").append("score", 6).append("comment", "very good")));Document doc3 = new Document("title", "good night").append("owner", "mike").append("words", 200).append("tag", Arrays.asList(1, 2, 3, 4));Document doc4 = new Document("title", "happiness").append("owner", "tom").append("words", 1480).append("tag", Arrays.asList(2, 3, 4));Document doc5 = new Document("title", "a good thing").append("owner", "tom").append("words", 180).append("tag", Arrays.asList(1, 2, 3, 4, 5));mc.insertMany(Arrays.asList(doc1, doc2, doc3, doc4, doc5));//测试: 查询全部FindIterable<Document> iterable = mc.find();printResult("find all", iterable);//TODO: 将在这里填充更多查询示例}//打印查询的结果集public void printResult(String doing, FindIterable<Document> iterable) {System.out.println(doing);iterable.forEach(new Block<Document>() {public void apply(final Document document) {System.out.println(document);}});System.out.println("------------------------------------------------------");System.out.println();}
}

如上面代码所示，把所有的查询操作集中在show()方法中演示，并且在执行后打印结果集以观察查询结果。下面来填充show()方法

//创建单字段索引
mc.createIndex(new Document("words", 1));
//创建组合索引(同样遵循最左前缀原则)
mc.createIndex(new Document("title", 1).append("owner", -1));
//创建全文索引
mc.createIndex(new Document("title", "text"));//查询全部
FindIterable<Document> iterable = mc.find();
printResult("find all", iterable);//查询title=good
iterable = mc.find(new Document("title", "good"));
printResult("find title=good", iterable);//查询title=good and owner=tom
iterable = mc.find(new Document("title", "good").append("owner", "tom"));
printResult("find title=good and owner=tom", iterable);//查询title like %good% and owner=tom
iterable = mc.find(and(regex("title", "good"), eq("owner", "tom")));
printResult("find title like %good% and owner=tom", iterable);//查询全部按title排序
iterable = mc.find().sort(ascending("title"));
printResult("find all and ascending title", iterable);//查询全部按owner,title排序
iterable = mc.find().sort(ascending("owner", "title"));
printResult("find all and ascending owner,title", iterable);//查询全部按words倒序排序
iterable = mc.find().sort(descending("words"));
printResult("find all and descending words", iterable);//查询owner=tom or words>350
iterable = mc.find(new Document("$or", Arrays.asList(new Document("owner", "tom"), new Document("words", new Document("$gt", 350)))));
printResult("find owner=tom or words>350", iterable);//返回title和owner字段
iterable = mc.find().projection(include("title", "owner"));
printResult("find all include (title,owner)", iterable);//返回除title外的其他字段
iterable = mc.find().projection(exclude("title"));
printResult("find all exclude title", iterable);//不返回_id字段
iterable = mc.find().projection(excludeId());
printResult("find all excludeId", iterable);//返回title和owner字段且不返回_id字段
iterable = mc.find().projection(fields(include("title", "owner"), excludeId()));
printResult("find all include (title,owner) and excludeId", iterable);//内嵌文档匹配
iterable = mc.find(new Document("comments.author", "joe"));
printResult("find comments.author=joe", iterable);//一个错误的示例, 想查询评论中包含作者是white且分值>2的, 返回结果不符合预期
iterable = mc.find(new Document("comments.author", "white").append("comments.score", new Document("$gt", 2)));
printResult("find comments.author=white and comments.score>2 (wrong)", iterable);//上面的需求正确的写法
iterable = mc.find(Projections.elemMatch("comments", Filters.and(Filters.eq("author", "white"), Filters.gt("score", 2))));
printResult("find comments.author=white and comments.score>2 using elemMatch", iterable);//查找title以good开头的, 并且comments只保留一个元素
iterable = mc.find(Filters.regex("title", "^good")).projection(slice("comments", 1));
printResult("find regex ^good and slice comments 1", iterable);//全文索引查找
iterable = mc.find(text("good"));
printResult("text good", iterable);//用Filters构建的title=good
iterable = mc.find(eq("title", "good"));
printResult("Filters: title eq good", iterable);//$in 等同于sql的in
iterable = mc.find(in("owner", "joe", "john", "william"));
printResult("Filters: owner in joe,john,william", iterable);//$nin 等同于sql的not in
iterable = mc.find(nin("owner", "joe", "john", "tom"));
printResult("Filters: owner nin joe,john,tom", iterable);//查询内嵌文档
iterable = mc.find(in("comments.author", "joe", "tom"));
printResult("Filters: comments.author in joe,tom", iterable);//$ne 不等于
iterable = mc.find(ne("words", 300));
printResult("Filters: words ne 300", iterable);//$and 组合条件
iterable = mc.find(and(eq("owner", "tom"), gt("words", 300)));
printResult("Filters: owner eq tom and words gt 300", iterable);//较复杂的组合
iterable = mc.find(and(or(eq("words", 300), eq("words", 400)), or(eq("owner", "joe"), size("comments", 2))));
printResult("Filters: (words=300 or words=400) and (owner=joe or size(comments)=2)", iterable);//查询第2个元素值为2的数组
iterable = mc.find(eq("tag.1", 2));
printResult("Filters: tag.1 eq 2", iterable);//查询匹配全部值的数组
iterable = mc.find(all("tag", Arrays.asList(1, 2, 3, 4)));
printResult("Filters: tag match all (1, 2, 3, 4)", iterable);//$exists
iterable = mc.find(exists("tag"));
printResult("Filters: exists tag", iterable);iterable = mc.find(type("words", BsonType.INT32));
printResult("Filters: type words is int32", iterable);

这里列出的查询方式可以覆盖到大部分开发需求，更多查询需求请参考官方文档。

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