Java程序中操作MongoDB数据库基础入门

and assuming that there are two collections, name and address, in the database, you would see

假如数据库中有name和address两个collection，结果输出入下

as the output.

 Getting A Collection

得到Collection

To get a collection to use, just specify the name of the collection to the getCollection(String collectionName) method:

要使用collection，使用getCollection(String collectionName) 方法传入collection的名称：

Once you have this collection object, you can now do things like insert data, query for data, etc

得到collection对象后就可以进行插入、查询等操作了。

插入一个文档（类似一条记录）

Once you have the collection object, you can insert documents into the collection. For example, lets make a little document that in JSON would be represented as

得到collection对象就可以把documents插入到collection中。例如，创建一个如下的JSON文档

Notice that the above has an "inner" document embedded within it. To do this, we can use the BasicDBObject class to create the document (including the inner document), and then just simply insert it into the collection using the insert() method.

注意，上面的文档中有个内部文档（就是{ x : 203, y : 102}）。存储上面的文档，可以使用BasicDBObject 类来创建文档（包括inner文档），使用insert()方法可以简单的把文档插入collection中。

使用findOne()方法查找collection中的第一个文档document

To show that the document we inserted in the previous step is there, we can do a simple findOne() operation to get the first document in the collection. This method returns a single document (rather than the DBCursor that the find() operation returns), and it's useful for things where there only is one document, or you are only interested in the first. You don't have to deal with the cursor.

可以使用findOne()操作来查找collection中的第一个文档来显示上一步中插入的文档。方法返回一个文档，用来找只有一个文档或第一条文档很实用。可以不使用cursor（游标）

Note the _id element has been added automatically by MongoDB to your document. Remember, MongoDB reserves element names that start with "_"/"$" for internal use.

注意，_id元素是MongoDB自动添加的。MongoDB内部的元素以"_"/"$"开始。

添加多个文档

In order to do more interesting things with queries, let's add multiple simple documents to the collection. These documents will just be

为了方便下面的讲解，我们来添加多个简单的文档，入下

and we can do this fairly efficiently in a loop

用循环来快速的实现

Notice that we can insert documents of different "shapes" into the same collection. This aspect is what we mean when we say that MongoDB is "schema-free"

注意，可以在一个collection中插入不同类型的文档。就是说MongoDB是"schema-free"（什么意思？）

统计collection中所有的document数量

Now that we've inserted 101 documents (the 100 we did in the loop, plus the first one), we can check to see if we have them all using the getCount() method.

现在，插入了101个文档（循环的100个和第一个），使用getCount()检查一下。

and it should print 101.

输出结果是101.

使用游标查找所有的文档

In order to get all the documents in the collection, we will use the find() method. The find() method returns a DBCursor object which allows us to iterate over the set of documents that matched our query. So to query all of the documents and print them out :

使用find()来查找所有的document。find()方法查询返回一个可以遍历文档集合的DBCursor 对象。如下：

and that should print all 101 documents in the collection.

打印所有的document

Getting A Single Document with A Query

查询出单个文档

We can create a query to pass to the find() method to get a subset of the documents in our collection. For example, if we wanted to find the document for which the value of the "i" field is 71, we would do the following ;

可以通过find()方法查找部分document，例如，如果想查找i=71的document，这样做

and it should just print just one document

会打印找到的单个document

MongoDB文档和例子中经常出现$操作符，如下

These are represented as regular String keys in the Java driver, using embedded DBObjects:

他表示驱动中预设的字符：

查找多个文档

We can use the query to get a set of documents from our collection. For example, if we wanted to get all documents where "i" > 50, we could write :

例如，想找"i">50的文档，这样做：

which should print the documents where i > 50. We could also get a range, say 20

会打印出i>50的文档。也可以查找范围如20 query = new BasicDBObject();
query.put("i", new BasicDBObject("$gt", 20).append("$lte", 30));  // i.e.   20 < i <= 30
cur = coll.find(query);
while(cur.hasNext()) {
    System.out.println(cur.next());
}
Creating An Index

创建索引