在mongodb集合中找到一些值? [英] Find some values in a mongodb collection?

问题描述

我正在尝试使用Java读取(mongo)用户数据库.在教程页面上，我看到了如何阅读整个收藏集.我可以做这样的事情:

Im trying to read a (mongo)userdatabase with java. On the tutorial page I saw how to read the whole collection. I can do something like that:

    DBCursor cursor = col.find();
    while (cursor.hasNext()) {
        System.out.println(cursor.next());
    }

现在，如果我有一个包含用户的收藏集:=名称，年龄，密码(...)等.现在，我想找到一个带有密码的名称.例如用于登录过程.可以说我有两个字符串:字符串n和p.如果数据库中存在user.equals(n)和password.equals(p)，则登录用户.我该如何更改光标?我在mongodb Java教程页面上看到了一些查询示例，但是我真的不明白...

Now if I have a collection with users := name, age, password (...) and whatever. Now I would like to find a name with a password. For example for a login process. Lets say I have two strings: String n and p. If there is a user.equals(n) and a password.equals(p) in the database then login user. How do I have to change my cursor? I saw some query examples on the mongodb java tutorial page, but duh I really dont get it...

有什么想法吗?谢谢

推荐答案

太棒了，您会爱上Mongo的.

Awesome, you'll love Mongo.

在您发布的示例中，该程序遍历一组结果.在用户/密码问题中，您描述了您实际要执行的操作是根据某些条件获得一个文档(而不是一组文档).

In the example you posted, the program iterates through a set of results. In the user/password problem you describe what you are actually trying to do is get one document (not a set of documents) based on some criteria.

在看起来像这样的外壳上:

On the shell that would look like this:

n = "login"
p = "password"

db.users.findOne({ user: n, password: p})

注意，我使用的是findOne而不是find，它会返回一个文档，而不是将光标指向许多文档.

Notice I'm using findOne instead of find which returns a document instead of a cursor to many documents.

现在，让我们看一下Java驱动程序的示例:

Now, lets take a look at the java driver's example:

BasicDBObject query = new BasicDBObject();

query.put("i", 71);
cur = coll.find(query);

while(cur.hasNext()) {
    System.out.println(cur.next());
}

BasicDBObject创建查询对象，然后将不同的条件组合在一起构成查询.

The BasicDBObject creates the query object and then you put different criteria which together form your query.

因此，代替query.put("i", 71);，您将执行以下操作:

So instead of query.put("i", 71); you would do something like:

query.put("user", n)
query.put("password", p)

and ...而不是while循环，而是使用findOne而不是find，因此您不必遍历1个对象的结果集(毫无意义).

and... instead of the while loop just use findOne instead of find so you don't have to iterate over the result set of 1 object (pointless).

您可以阅读有关findOne()的更多信息此处.

You can read more about findOne() here.

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