Exposed
 
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  2. Working with Databases

Working with Databases

Last modified: 03 March 2025

In Exposed, the Database class represents a database instance, and encapsulates the necessary connection details and configuration required to interact with a specific database.

Connecting to a Database

Every database access using Exposed is started by obtaining a connection and creating a transaction.

First of all, you have to tell Exposed how to connect to a database by using the Database.connect() function. It won't create a real database connection but will only provide a descriptor for future usage.

A real connection will be instantiated later by calling the transaction lambda (see Transactions for more details).

Use the following to get a Database instance by simply providing connection parameters:

val db = Database.connect("jdbc:h2:mem:test", driver = "org.h2.Driver")

note

Executing this code more than once per database will create leaks in your application, hence it is recommended to store it for later use: 

object DbSettings {
    val db by lazy {
        Database.connect(/* setup connection */)
    }
}

note

By default, Exposed uses a ServiceLoader to get an implementation of the DatabaseConnectionAutoRegistration interface that represents a connection accessed by the Database instance. This can be modified when calling the Database.connect() method by providing an argument to connectionAutoRegistration in the parameter list.

H2

In order to use H2, you need to add the H2 driver dependency:

implementation("com.h2database:h2:2.2.224")

Then connect to a database:

Database.connect("jdbc:h2:./myh2file", "org.h2.Driver")

Or in-memory database:

Database.connect("jdbc:h2:mem:regular", "org.h2.Driver")

By default, H2 closes the database when the last connection is closed. If you want to keep the database open, you can use the DB_CLOSE_DELAY=-1 option:

Database.connect("jdbc:h2:mem:regular;DB_CLOSE_DELAY=-1;", "org.h2.Driver")

MariaDB

Add dependency:

implementation("org.mariadb.jdbc:mariadb-java-client:3.3.1")

Connect to database:

Database.connect("jdbc:mariadb://localhost:3306/test",
    driver = "org.mariadb.jdbc.Driver",
    user = "root",
    password = "your_pwd"
)

MySQL

Add dependency:

implementation("mysql:mysql-connector-java:8.0.33")

Connect to database:

Database.connect(
    "jdbc:mysql://localhost:3306/test",
    driver = "com.mysql.cj.jdbc.Driver",
    user = "user",
    password = "password"
)

Oracle

Add dependency:

implementation("com.oracle.database.jdbc:ojdbc8:12.2.0.1")

Connect to database:

Database.connect(
    "jdbc:oracle:thin:@//localhost:1521/test",
    driver = "oracle.jdbc.OracleDriver",
    user = "user",
    password = "password"
)

PostgreSQL

Add dependency:

implementation("org.postgresql:postgresql:42.7.1")

Connect to database:

Database.connect(
    "jdbc:postgresql://localhost:12346/test",
    driver = "org.postgresql.Driver",
    user = "user",
    password = "password"
)

PostgreSQL using the pgjdbc-ng JDBC driver

Add dependency:

implementation("com.impossibl.pgjdbc-ng", "pgjdbc-ng", "0.8.9")

Connect to database:

Database.connect(
    "jdbc:pgsql://localhost:12346/test",
    driver = "com.impossibl.postgres.jdbc.PGDriver",
    user = "user",
    password = "password"
)

SQL Server

Add dependency:

implementation("com.microsoft.sqlserver:mssql-jdbc:9.4.1.jre8")

Connect to database:

Database.connect(
    "jdbc:sqlserver://localhost:32768;databaseName=test",
    "com.microsoft.sqlserver.jdbc.SQLServerDriver",
    user = "user",
    password = "password"
)

SQLite

Add the dependency:

implementation("org.xerial:sqlite-jdbc:3.44.1.0")

Connect to database:

Database.connect("jdbc:sqlite:/data/data.db", "org.sqlite.JDBC")

Or in-memory database:

Database.connect("jdbc:sqlite:file:test?mode=memory&cache=shared", "org.sqlite.JDBC")

Set SQLite compatible isolation level:

TransactionManager.manager.defaultIsolationLevel = Connection.TRANSACTION_SERIALIZABLE
// or Connection.TRANSACTION_READ_UNCOMMITTED