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MongoDB
use mydatabase
3. If the specified database already exists, it will be selected. Otherwise, MongoDB will create a new database when you start adding data to it.
4. You can now start adding data to your new database or create collections within it.
db.collectionName.insertOne({ key: "value" })
Replace collectionName with the name you want to give to your collection and { key: "value" } with the data you want to insert.
5. MongoDB creates the new database when you first store data into it. Until then, the database will not be listed in the output of the show dbs command. To see the list of databases, you can use the following command:
show dbs
The new database will appear in the list once it contains data.
Remember, MongoDB is a schema-less database, which means that you don’t need to define the structure of the database or its collections explicitly before using them. You can start inserting data right away, and MongoDB will create collections and the database on the fly as necessary.
use mydatabase
If the specified database already exists, it will be selected. Otherwise, MongoDB will create a new database when you start adding data to it.
3. You can now start adding data to your new database or create collections within it. For instance, let’s create a collection named “mycollection” and insert a document into it:
db.mycollection.insertOne({ name: "John", age: 30 })
This command will create the “mycollection” collection within the “mydatabase” database and insert a document with the fields “name” and “age” into it.
4. To verify that the database has been created and switch to it, you can use the show dbs command. It will display a list of all available databases:
show dbs
The output will include the “mydatabase” in the list, and you can switch to it again using the use command:
use mydatabase
Now you are working within the “mydatabase” database and can perform further operations on its collections.
Remember, until you store data in the database, it may not appear in the show dbs output. MongoDB creates the new database when you start adding data to it.
db.createCollection(collectionName, options)
Here’s a breakdown of the parameters:
collectionName: The name of the collection you want to create. It should be a string.options(optional): An object that specifies additional options for the collection. This parameter is optional, and you can omit it if you don’t need to specify any options.
Let’s see an example of creating a new collection called “mycollection” with some options:
db.createCollection("mycollection", { capped: true, size: 8192, max: 100 })
In this example, we’re creating a collection named “mycollection” with the following options:
capped: true– This option creates a capped collection, which is a fixed-size collection that maintains the insertion order of documents. When the collection reaches its maximum size (sizeoption), older documents are overwritten with new ones.size: 8192– This option specifies the maximum size, in bytes, for the capped collection. In this case, it’s set to 8192 bytes (8KB).max: 100– This option sets the maximum number of documents the capped collection can hold. Once this limit is reached, older documents are overwritten with new ones.
You can customize the options based on your requirements or create a collection without any options by omitting the options parameter.
Note that when you insert documents into a collection, MongoDB will create the collection implicitly if it doesn’t exist already. The db.createCollection() method provides explicit control over the collection’s options and allows you to create it before inserting any documents if needed.
use mydatabase
If the database exists, the shell prompt will change to mydatabase, indicating its existence. If it doesn’t exist, MongoDB will create it once you store data in it.
2. List All Available Databases:
In the MongoDB shell, use the
show dbscommand to list all available databases in the MongoDB instance.This command displays a list of databases along with their sizes.
show dbs
The output will include all the existing databases, along with their sizes in bytes. However, it’s important to note that databases without any data (no documents inserted) may not appear in the show dbs output.
Remember that in MongoDB, databases are created implicitly when data is stored in them or explicitly when you switch to a non-existing database and perform data operations. The 'show dbs' command provides an overview of all databases that have data stored in them.
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