In this article, we'll take a look at how to connect to a MongoDB database from Kotlin. MongoDB is a open source document-oriented database system that uses JSON-like documents with schemas. It's a popular choice for web applications and is also suitable for storing data in many Kotlin applications.
We'll start by looking at how to install MongoDB. Then we'll create a Kotlin project and connect it to our MongoDB database. We'll finish by looking at how to query our database from Kotlin.
MongoDB is available for Windows, MacOS, and Linux. You can download it from the MongoDB website. Make sure to download the version that matches your operating system.
Once you've downloaded MongoDB, unzip the archive and extract the contents to a location of your choice. For this article, we'll extract it to C:\mongodb
.
Next, we need to create a data directory for MongoDB. The data directory is where MongoDB will store its data files. Create a new directory called data
in your MongoDB installation directory.
Now that we have our data directory, we can start MongoDB. Open a terminal window and navigate to your MongoDB installation directory. Then run the following command:
mongod --dbpath C:\mongodb\data
This command starts the MongoDB server and tells it to use our data
directory as the data directory. MongoDB will now be running in the background. You can leave this terminal window open or close it, as we won't be needing it again.
We're now ready to start developing our Kotlin application. We'll be using the Gradle build system for this project. Create a new directory for your project and navigate to it in a terminal window. Then run the following command to create a new Gradle project:
gradle init --type kotlin-library
This command will create a new Kotlin project with the kotlin-library
plugin. This plugin is used for developing Kotlin libraries. We won't be using this plugin for our project, but we'll be using it anyway as it includes the kotlin-stdlib
dependency, which we need.
Now that we have our project set up, we can start adding dependencies. The first dependency we need is the MongoDB Driver. The MongoDB Driver is a library that allows us to connect to and query MongoDB from Kotlin. You can find the latest version of the MongoDB Driver on the Maven Central Repository.
Add the following to your build.gradle
file:
repositories {
jcenter()
}
dependencies {
implementation "org.mongodb:mongodb-driver:3.12.4"
}
The first line adds the JCenter repository to our project. JCenter is a repository that hosts a lot of popular Java libraries. The second line adds the MongoDB Driver dependency. Replace 3.12.4
with the latest version of the MongoDB Driver.
Now that we have the MongoDB Driver dependency, we can start writing code. We'll start by creating a Database
object that represents our MongoDB database. Add the following code to your main.kt
file:
val database: Database = Database("mongodb://localhost:27017/test")
This code creates a Database
object that represents the test
database on our MongoDB server. The mongodb
protocol specifies that we're connecting to MongoDB. The localhost
part specifies the hostname of our MongoDB server. The 27017
is the port that MongoDB is running on. The test
part is the name of the database we want to connect to.
Now that we have a Database
object, we can start querying our database. We'll start by querying for all the documents in our database. Add the following code to your main.kt
file:
val documents: List<Document> = database.find()
This code querys our database for all the documents and returns them as a list of Document
objects.
We can also query for specific documents. For example, we can query for all the documents that have an _id
field with the value 1
. Add the following code to your main.kt
file:
val document: Document? = database.findOne(Document("_id", 1))
This code queries our database for a document with an _id
field of 1
and returns it as a Document
object. If no such document exists, it returns null
.
We can also insert documents into our database. For example, we can insert a document with an _id
field of 1
and a name
field of John
. Add the following code to your main.kt
file:
database.insertOne(Document("_id", 1).append("name", "John"))
This code inserts a document with an _id
field of 1
and a name
field of John
into our database.
We can also update documents in our database. For example, we can update the document we just inserted so that the name
field has a value of Jane
. Add the following code to your main.kt
file:
database.updateOne(Document("_id", 1), Document("\$set", Document("name", "Jane")))
This code updates the document with an _id
field of 1
so that the name
field has a value of Jane
.
In this article, we've looked at how to connect to a MongoDB database from Kotlin. We've also seen how to query and update documents in our database. For more information, see the MongoDB Driver documentation.