Since Grails is built on Java technology setting up a data source requires some knowledge of JDBC (the technology that doesn't stand for Java Database Connectivity).

Essentially, if you are using another database other than HSQLDB you need to have a JDBC driver. For example for MySQL you would need Connector/J

Drivers typically come in the form of a JAR archive. Drop the JAR into your project's lib directory.

Once you have the JAR in place you need to get familiar Grails' DataSource descriptor file located at grails-app/conf/DataSource.groovy. This file contains the dataSource definition which includes the following settings:

A typical configuration for MySQL may be something like:

dataSource {
    pooled = true
    dbCreate = "update"
    url = "jdbc:mysql://localhost/yourDB"
    driverClassName = "com.mysql.jdbc.Driver"
    dialect = org.hibernate.dialect.MySQL5InnoDBDialect
    username = "yourUser"
    password = "yourPassword"
}

When configuring the DataSource do not include the type or the def keyword before any of the configuration settings as Groovy will treat these as local variable definitions and they will not be processed. For example the following is invalid:

dataSource {
    boolean pooled = true // type declaration results in local variable
    …
}

Example of advanced configuration using extra properties:

dataSource {
    pooled = true
    dbCreate = "update"
    url = "jdbc:mysql://localhost/yourDB"
    driverClassName = "com.mysql.jdbc.Driver"
    dialect = org.hibernate.dialect.MySQL5InnoDBDialect
    username = "yourUser"
    password = "yourPassword"
    properties {
        maxActive = 50
        maxIdle = 25
        minIdle = 5
        initialSize = 5
        minEvictableIdleTimeMillis = 60000
        timeBetweenEvictionRunsMillis = 60000
        maxWait = 10000
        validationQuery = "/* ping */"
    }
}

More on dbCreate

Hibernate can automatically create the database tables required for your domain model. You have some control over when and how it does this through the dbCreate property, which can take these values:

You can also remove the dbCreate setting completely, which is recommended once you have an application and database in production. Database changes then have to be managed through proper migrations, either via SQL scripts or a migration tool like Liquibase (for which there is a plugin).