java MongoDB查询（一）简单查询

前言

        MongoDB的java驱动提供了查询的功能，查询条件也是bson对象，这篇就看下怎么进行简单的数据查询

1、数据结构

        集合：firstCollection

        数据内容：

        { "_id" : ObjectId("55adba52fa1f3cf038c2aea6"), "name" : "user0", "age" : 22, "sex" : 0 }

        { "_id" : ObjectId("55adba52fa1f3cf038c2aea7"), "name" : "user1", "age" : 23, "sex" : 1 }

        { "_id" : ObjectId("55adba52fa1f3cf038c2aea8"), "name" : "user2", "age" : 24, "sex" : 0 }

        { "_id" : ObjectId("55adba52fa1f3cf038c2aea9"), "name" : "user3", "age" : 25, "sex" : 1 }

        { "_id" : ObjectId("55adba52fa1f3cf038c2aeaa"), "name" : "user4", "age" : 26, "sex" : 0 }

        { "_id" : ObjectId("55adba52fa1f3cf038c2aeab"), "name" : "user5", "age" : 27, "sex" : 1 }

2、连接数据库，拿到集合firstCollection

        MongoClient mClient = new MongoClient("10.211.55.8");

        DB db = mClient.getDB("test");

        DBCollection collection = db.getCollection("firstCollection");

3、查询name为user1的对象

        查询条件Json内容：

        {"name": "user1"}

        查询条件Java内容：

        BasicDBObject queryObject = new BasicDBObject("name","user1");

        执行过程：

        DBObject obj = collection.findOne(queryObject);

        这样就拿到了name为user1的对象了

4、查询name包含user的对象

        这样模糊查询，也就类似于like查询是通过正则表达式来完成的

        查询条件Json内容：

        {“name”:/user/}

        查询条件Java内容：

        Pattern queryPattern = Pattern.compile("user", Pattern.CASE_INSENSITIVE);

        BasicDBObject queryObject = new BasicDBObject("name",queryPattern);

        执行过程：

        Pattern queryPattern = Pattern.compile("user", Pattern.CASE_INSENSITIVE);

        BasicDBObject queryObject = new BasicDBObject("name",queryPattern);

        Cursor cursor = collection.find(queryObject);

        while(cursor.hasNext()){

                DBObject obj = cursor.next();

                System.out.println(obj.toString());

        }        

5、查询年龄大于24的对象

        查询条件Json内容：

        {"age":{"$gt":24}}

        

        查询条件Java内容:

        两个Bson对象嵌套

        BasicDBObject gt = new BasicDBObject("$gt",24);

        BasicDBObject queryObject = new BasicDBObject("age",gt);        

        

        执行过程：

        BasicDBObject gt = new BasicDBObject("$gt",24);

        BasicDBObject queryObject = new BasicDBObject("age",gt);

        Cursor cursor = collection.find(queryObject);

        while(cursor.hasNext()){

                DBObject obj = cursor.next();

                System.out.println(obj.toString());

        }

        备注：

        $gt：>

        $gte：>=

        $eq:        =

        $ne:        !=

        $lt:        <

        $lte:        <=

        $in:        in(后面的值为bson对象数组)

        $nin:        not in(后面的值为bson对象数组)

        这些操作符的用法和$gt类似，不在赘述

总结

        通过这篇文章就可以对MongoDB进行简单的查询了，但是在具体业务中只有简单查询是不现实的，会有更多的与或关系，这戏内容将在下次文章中叙述。