In this article we'll explore how to connect to a MySQL database from Kotlin. We'll look at how to configure the database, write code to perform various operations, and handle errors.
Before we can start writing code, we need to configure our database. We'll assume that you have MySQL installed and running on your local machine. If not, you can download it here.
Once MySQL is up and running, we need to create a database and a user that our Kotlin code can use. We can do this by logging into the MySQL console:
mysql> CREATE DATABASE kotlindb;
Query OK, 1 row affected (0.01 sec)
mysql> CREATE USER 'kotlinuser'@'localhost' IDENTIFIED BY 'password';
Query OK, 0 rows affected (0.00 sec)
mysql> GRANT ALL PRIVILEGES ON kotlindb.* TO 'kotlinuser'@'localhost';
Query OK, 0 rows affected (0.00 sec)
Now that our database is configured, we can write some Kotlin code to connect to it. We'll use the JDBC driver for MySQL, which you can add to your project by including the following dependency in your build.gradle
file:
dependencies {
implementation 'mysql:mysql-connector-java:8.0.21'
}
With the JDBC driver in place, we can write a Kotlin function to connect to the database:
fun connectToDatabase(): Connection? {
val url = "jdbc:mysql://localhost:3306/kotlindb"
val user = "kotlinuser"
val password = "password"
return try {
DriverManager.getConnection(url, user, password)
} catch (e: SQLException) {
null
}
}
This function tries to connect to the database using the url
, user
, and password
that we configured earlier. If the connection is successful, it returns the Connection
object. If the connection fails, it returns null
.
Now that we have a way to connect to the database, we can start writing code to perform various operations. We'll start with a simple example: querying the database for a list of all users.
First, we'll need to write a SQL query:
SELECT * FROM users
Next, we'll write a Kotlin function to execute this query:
fun getAllUsers(connection: Connection): List<User> {
val sql = "SELECT * FROM users"
val statement = connection.createStatement()
val resultSet = statement.executeQuery(sql)
val users = ArrayList<User>()
while (resultSet.next()) {
val id = resultSet.getInt("id")
val name = resultSet.getString("name")
val email = resultSet.getString("email")
val user = User(id, name, email)
users.add(user)
}
return users
}
This function takes a Connection
object as a parameter. It then creates a Statement
object and uses it to execute the SQL query. The executeQuery
method returns a ResultSet
object, which contains the results of the query.
We can use the next
method of the ResultSet
object to loop through the results. For each result, we create a User
object and add it to the users
list. Finally, we return the users
list.
So far we've seen how to connect to the database and perform various operations. But what happens if something goes wrong? For example, what if the database is down or the SQL query is invalid?
In Kotlin, we can use the try
/catch
mechanism to handle errors. Let's modify our getAllUsers
function to use try
/catch
:
fun getAllUsers(connection: Connection): List<User> {
val sql = "SELECT * FROM users"
return try {
val statement = connection.createStatement()
val resultSet = statement.executeQuery(sql)
val users = ArrayList<User>()
while (resultSet.next()) {
val id = resultSet.getInt("id")
val name = resultSet.getString("name")
val email = resultSet.getString("email")
val user = User(id, name, email)
users.add(user)
}
users
} catch (e: SQLException) {
println("An error occurred while executing the SQL query: $sql")
println(e.message)
ArrayList()
}
}
In this version of the getAllUsers
function, we've wrapped the code in a try
block. If an SQLException
is thrown, the code in the catch
block will be executed. In this case, we're simply printing an error message.
It's important to note that the try
/catch
mechanism is only suitable for handling errors that can be recover from. For example, if the database is down, we can't do anything to recover from the error, so try
/catch
won't be of any use.
In this article we've seen how to connect to a MySQL database from Kotlin. We've looked at how to configure the database, write code to perform various operations, and handle errors.