How to view all databases in MongoDB

The way to view all databases in MongoDB is to enter the command "show dbs". 1. This command displays only non-empty databases. 2. You can switch the database through the "use" command and insert data to display it. 3. Pay attention to internal databases such as "local" and "config". 4. When using the driver, you need to use the "listDatabases()" method to obtain detailed information. 5. The "db.stats()" command can view detailed database statistics.

The way to view all databases in MongoDB is actually very simple, but it's just the tip of the iceberg. Let's explore this topic in depth and share some of my own experiences and tips when using MongoDB.

To view all databases in MongoDB, you just need to enter a simple command in the MongoDB shell:

 show dbs

This command lists all available databases. But do you know? It is not enough to just know this command, we need to have a deeper understanding of why this command is so useful and some of the problems that may be encountered in actual use.

First, when you execute show dbs , MongoDB displays all non-empty databases. This means that if you create a database but don't insert any data, it won't show up in the list. This can cause some confusion when you manage multiple projects or environments because you may think that a certain database does not exist. One way to solve this problem is to use the use command to switch to the database you think exists and insert a record so that it will be displayed in show dbs .

 use myDatabase
db.myCollection.insertOne({ test: "data" })

When using show dbs , you may notice that some database names look weird, such as those with . These are usually databases used internally by MongoDB, such as local and config . Understanding the role of these databases can help you better manage and optimize your MongoDB instances.

Another thing to note is that the show dbs command is actually a secondary command of the MongoDB shell, not a command from the MongoDB server itself. This means that if you interact with MongoDB through a driver or API, you need to use a different approach to get the database list. For example, in MongoDB's Node.js driver, you can do this:

 const MongoClient = require('mongodb').MongoClient;
const url = 'mongodb://localhost:27017';

MongoClient.connect(url, function(err, client) {
  if (err) throw err;
  const adminDb = client.db().admin();
  adminDb.listDatabases().then(function(dbs) {
    console.log(dbs.databases);
    client.close();
  });
});

This method will return an object containing all database information, including not only the database name, but also the database size and other information, which will be more useful in some cases than show dbs .

In actual use, I found a common misunderstanding that show dbs will display the details of all databases. Actually, it's just a simple list. If you need more information, such as the size of the database, storage engine, etc., you need to use db.stats() command.

 use myDatabase
db.stats()

This command will return detailed statistics of the current database, including data size, index size, etc., which is very useful for performance optimization and resource management.

Finally, share a tip: If you often need to view a database list of multiple MongoDB instances, you can write a simple script to automate the process. This not only saves time, but also reduces manual operation errors.

 const MongoClient = require('mongodb').MongoClient;

async function listDatabases(url) {
  const client = await MongoClient.connect(url);
  const adminDb = client.db().admin();
  const dbs = await adminDb.listDatabases();
  console.log(`Databases in ${url}:`);
  dbs.databases.forEach(db => console.log(db.name));
  await client.close();
}

const urls = ['mongodb://localhost:27017', 'mongodb://anotherhost:27017'];

urls.forEach(url => listDatabases(url).catch(console.error));

This script can traverse multiple MongoDB instances and list the databases in each instance, which is very convenient.

Overall, show dbs is a very basic but useful command, but to really master the use of MongoDB, you need to know more details and techniques. Hope these sharing can help you better use MongoDB.

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