As you know, MongoDB is used for various purposes such as application development, data analysis, and more. In all these cases, we need to interact with the MongoDB server to add new data, update existing data, retrieve information, or remove invalid records.
To facilitate these interactions, MongoDB provides a set of commands that simplify the process. These commands, which make working with MongoDB easier, are known as CRUD operations.
There are several operators for creating or adding a document to collections in a MongoDB database.
If the target collection does not exist, MongoDB will create it before adding the new document.
| Method | Description |
|---|---|
db.collection.insertOne() |
Inserts a single document into a collection. |
db.collection.insertMany() |
Inserts multiple documents into a collection. |
db.createCollection() |
Creates an empty collection. |
As you can see in the image below, a collection named students has already been created and contains 4 documents.
According to the image, we added a new document with the ID of 5 to the collection.
If the operation is successful, the value of acknowledged will be true.
To simplify the process and to add multiple documents at once, we use the insertMany() command.
As shown in the image below, its input is an array.
In the image, two new documents related to students with IDs 6 and 7 have been added to the students collection.
The Read operator is used to retrieve documents from collections.
This can be done using the find() or findOne() methods.
Often, the pretty() method is used immediately after to make the output more readable.
The find() method has several useful operators.
Update operators are designed to apply changes to existing documents in collections.
To perform such operations, MongoDB provides the following methods:
| Method | Description |
|---|---|
db.collection.updateOne(given criteria) |
Used to update a single document in the collection if it meets the given criteria. |
db.collection.updateMany(given criteria) |
Used to update multiple documents in the collection if they meet the given criteria. |
db.collection.replaceOne(given criteria) |
Used to replace a document in the collection if it meets the given criteria. |
As shown in the image below, the written command instructs MongoDB to update the first document whose name starts with std, changing it to the value StudentName. Since the updateOne method is used, only the first document that matches the given criteria will be updated.
If the command is executed using the updateMany method instead, all documents that meet the specified condition will be updated.
Note: It is recommended to evaluate the conditions using the
findmethod before using update commands to avoid unintended data modifications.
Using the delete operators provided by MongoDB, you can remove documents from collections. To do this, you can use one of the following methods:
| Method | Description |
|---|---|
db.collection.deleteOne(criteria) |
Deletes only one document that matches the given criteria. |
db.collection.deleteMany(criteria) |
Deletes all documents that match the given criteria. |
As shown in the image below, although there are multiple documents that match the condition, only the first matching document is deleted when using the deleteOne() method.
The output of the function indicates the number of documents that have been removed from the collection.
We then execute the deleteMany() method with the same condition on the collection. This time, all documents that match the condition will be deleted.
As shown in the image below, 4 records were deleted.
