Node.js - Mongoose - 检查集合是否存在 [英] Node.js - Mongoose - Check if a collection exists

问题描述

我需要使用 mongoose 插入一些数据，但是集合的名称是在插入时用户提供的，所以我首先要检查集合是否存在.

I need to insert some data using mongoose but the name of the collection is provided by the user at the moment of the insertion, so I first have to check if the collection exists.

我知道如何检查集合是否存在的方法是查询 system.namespaces 集合.我可以看到 3 种可能的方法来做到这一点.

The way I know how to check if a collection exists is by querying the system.namespaces collection. I can see 3 possible approaches to doing that.

1. 找到一种使用 mongoose 查询 system.namespaces 的方法(可能定义一个与数据库中的模式匹配的模式).
2. 从 mongoose 获取一些底层 node-mongodb-native 对象并手动执行查询.无论如何，这是我想学习如何做的事情.
3. 使用 node-mongodb-native(或其他一些驱动程序)的单独实例来执行查询

1. Find a way to query system.namespaces using mongoose (maybe defining a schema that matches the one in the db).
2. Getting some underlying node-mongodb-native object from mongoose and performing the query manually. In any case, this is something I would like to learn how to do.
3. Using a separate instance of a node-mongodb-native (or some other driver) to perform the query

数字 3 是最不优雅的，也是我试图避免的，我不想加载驱动程序的另一个实例，也不想在猫鼬已经创建一个连接时创建新连接.

Number 3 is the least elegant and the one i'm trying to avoid, I don't want to load another instance of the driver nor create a new connection when mongoose already created one.

我将在写完这篇文章后尝试编号 1.我刚刚检查了 system.namespaces 并且架构看起来很简单

I'm going to try number 1 after writing this. I just checked system.namespaces and the schema looks quite simple

我还是想听听大家的意见.

I'd still like to hear some opinions.

谢谢！

推荐答案

选项 2 可能是最干净的.假设您有一个名为 conn 的 Mongoose Connection 对象已使用 mongoose.createConnection 打开，您可以访问本机 mongo Db 对象通过 conn.db.从那里你可以调用 collectionNames 应该提供您要查找的内容:

Option 2 is probably the cleanest. Assuming you have a Mongoose Connection object named conn that's been opened using mongoose.createConnection, you can access the native mongo Db object via conn.db. From there you can call collectionNames which should provide what you're looking for:

conn.db.collectionNames(function (err, names) {
    // names contains an array of objects that contain the collection names
});

您还可以将集合名称作为参数传递给 collectionNames 以将结果过滤为您要查找的内容.

You can also pass a collection name as a parameter to collectionNames to filter the results to just what you're looking for.

猫鼬 4.x 更新

在 Mongoose 4.x 使用的 MongoDB 本机驱动程序的 2.x 版本中，collectionNames 已被替换为 listCollections 它接受一个过滤器并返回一个游标，所以你可以这样做:

In the 2.x version of the MongoDB native driver that Mongoose 4.x uses, collectionNames has been replaced by listCollections which accepts a filter and returns a cursor so you would do this as:

mongoose.connection.db.listCollections({name: 'mycollectionname'})
    .next(function(err, collinfo) {
        if (collinfo) {
            // The collection exists
        }
    });

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