Working with DataSources

It is also possible to provide a javax.sql.DataSource to the Database.connect() function. This allows you to use more advanced features like connection pooling, and lets you set configuration options like maximum number of connections, connection timeouts, etc.

val db = Database.connect(dataSource)

Example with HikariCP

To use a JDBC connection pool like HikariCP, first set up a HikariConfig class. This example uses the MySQL JDBC driver (see the official reference for MySQL configuration details):

val config = HikariConfig().apply {
    jdbcUrl = "jdbc:mysql://localhost/dbname"
    driverClassName = "com.mysql.cj.jdbc.Driver"
    username = "username"
    password = "password"
    maximumPoolSize = 6
    // as of version 0.46.0, if these options are set here, they do not need to be duplicated in DatabaseConfig
    isReadOnly = false
    transactionIsolation = "TRANSACTION_SERIALIZABLE"
}

// Gradle
implementation "mysql:mysql-connector-java:8.0.33"
implementation "com.zaxxer:HikariCP:4.0.3"

Then instantiate a HikariDataSource with this configuration class and provide it to Database.connect():

val dataSource = HikariDataSource(config)

Database.connect(
    datasource = dataSource,
    databaseConfig = DatabaseConfig {
        // set other parameters here
    }
)

Since version 0.46.0, when configured directly in the HikariConfig class, values like transactionIsolation and isReadOnly will be used by Exposed when creating transactions. If they are duplicated or new values are set in DatabaseConfig, the latter will be treated as an override in the same way that setting these parameters on an individual transaction block overrides the default settings. It is therefore recommended to not set these values in DatabaseConfig unless the intention is for the new value to override the Hikari settings. {style="note"}