Java通过_id查询mongodb数据库

Bertha 。 2022-06-05 22:27 202阅读 0赞

本文以mongo-java-driver-3.5.0.jar为例

**1 \_id介绍：**  
MongoDB中存储的文档必须有一个”\_id”键，其对应的”\_id”值是由MongoDB服务器按照特定规律自动生成唯一的值，确保集合里面每个文档都能被唯一标识。这个键的值可以是任何类型的，默认是个ObjectId对象。

**2 MongoDB查询语句：**  
db.user.find(\{ “\_id” : ObjectId(“59c8cbea6157d6c78dab4ff0”) \})  
![这里写图片描述][SouthEast]

3 3中查询语句实现Java语句：

public static MongoCollection<Document> connect() {  
        @SuppressWarnings("resource")  
        MongoClient client = new MongoClient("127.0.0.1", 27017); 
        MongoDatabase db = client.getDatabase("test"); 
        MongoCollection<Document> collection = db.getCollection("user"); 
        return collection;
    } 
    public static List<Document> findBy1(DBObject filter) {  
        List<Document> results = new ArrayList<Document>(); 
        FindIterable<Document> iterables = connect().find((Bson) filter); 
        MongoCursor<Document> cursor = iterables.iterator(); 
        while (cursor.hasNext()) {  
            results.add(cursor.next()); 
        }  
    
        return results; 
    }
    
    @Test
    public void findById () {
        String _id = "59c8cbea6157d6c78dab4ff0";
    
        // 方法1
        DBObject filter = new BasicDBObject(); 
        filter.put("_id", new ObjectId(_id)); // 该写法在spring mvc + spring +hibernate项目中无效，具体原因不明确
        // filter.put("_id", _id); // 该写法在spring mvc + spring +hibernate项目中有效，具体原因不明确
        List<Document> results = findBy1(filter); 
        for(Document doc : results){  
            System.out.println("方法1：" + doc.toJson()); 
            // 方法1：{ "_id" : { "$oid" : "59c8cbea6157d6c78dab4ff0" }, "name" : "yy", "password" : "123", "nickname" : "ygirl2", "iid" : 2 }
        } 
    
        // 方法2
        Bson filter2 =  Filters.and(Filters.eq("_id", new ObjectId(_id)));
        List<Document> results2 = findBy(filter2); 
        for(Document doc : results2){  
            System.out.println("方法2：" +doc.toJson()); 
            // 方法2：{ "_id" : { "$oid" : "59c8cbea6157d6c78dab4ff0" }, "name" : "yy", "password" : "123", "nickname" : "ygirl2", "iid" : 2 }
        } 
    
        // 方法3
        Document filter3 = new Document(); 
        filter3.append("_id", new ObjectId(_id));
        List<Document> results3 = findBy(filter3); 
        for(Document doc : results3){  
            System.out.println("方法3：" +doc.toJson()); 
            // 方法3：{ "_id" : { "$oid" : "59c8cbea6157d6c78dab4ff0" }, "name" : "yy", "password" : "123", "nickname" : "ygirl2", "iid" : 2 } 
        } 
    }

[SouthEast]: /images/20220606/120e2e725cd14addbf339cf9bd691943.png