[Grails]PostgreSQLを使う

PostgreSQLに接続するのに必要なJDBCドライバを記述する

grails-app/conf/BuildConfig.groovy

    dependencies {
        // specify dependencies here under either 'build', 'compile', 'runtime', 'test' or 'provided' scopes e.g.
        runtime 'postgresql:postgresql:9.1-901.jdbc4'
    }

PostgreSQLに接続する為の情報を記述する

grails-app/conf/DataSource.groovy

dataSource {
    pooled = true
    driverClassName = "org.postgresql.Driver"
    username = [PostgreSQLのユーザ名]
    password = [PostgreSQLのパスワード]

}
hibernate {
    cache.use_second_level_cache = true
    cache.use_query_cache = false
    cache.region.factory_class = 'net.sf.ehcache.hibernate.EhCacheRegionFactory'
}
// environment specific settings
environments {
    development {
        dataSource {
            url = "jdbc:postgresql://[IPアドレスとかホスト名とか]:[ポート番号]/[DB名]"
        }
    }
    test {
        基本的にurlを変えるだけなので省略
    }
    production {
        基本的にurlを変えるだけなので省略
    }

コレで完了。
後はGrailsを起動すれば自動的にPostgreSQLに接続される。

例えば以下のようなドメインを適当に作って・・・

grails> create-domain-class service-test.Writer
| Created file grails-app/domain/service-test/Writer.groovy
| Created file test/unit/service-test/WriterSpec.groovy
grails> create-domain-class service-test.Book
| Created file grails-app/domain/service-test/Book.groovy
| Created file test/unit/service-test/BookSpec.groovy

Grailsをrun-appで起動すれば、自動的にテーブルが生成される。

Grails起動時に異常に長いエラー（例外）が出力される場合

以下のような例外が出力される事があります。

| Running Grails application
| Error 2014-01-12 03:59:50,510 [localhost-startStop-1] ERROR context.GrailsContextLoader  - Error initializing the application: Error creating bean with name 'transactionManagerPostProcessor': Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'transactionManager': Cannot resolve reference to bean 'sessionFactory' while setting bean property 'sessionFactory'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sessionFactory': Cannot resolve reference to bean 'dataSource' while setting bean property 'dataSource'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource': Cannot resolve reference to bean 'dataSourceLazy' while setting constructor argument; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSourceLazy': Cannot resolve reference to bean 'dataSourceUnproxied' while setting constructor argument; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSourceUnproxied': Error setting property values; nested exception is org.springframework.beans.PropertyBatchUpdateException; nested PropertyAccessExceptions (1) are:
PropertyAccessException 1: org.springframework.beans.MethodInvocationException: Property 'driverClassName' threw exception; nested exception is java.lang.IllegalStateException: Could not load JDBC driver class [org.postgresql.Driver]
Message: Error creating bean with name 'transactionManagerPostProcessor': Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'transactionManager': Cannot resolve reference to bean 'sessionFactory' while setting bean property 'sessionFactory'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sessionFactory': Cannot resolve reference to bean 'dataSource' while setting bean property 'dataSource'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource': Cannot resolve reference to bean 'dataSourceLazy' while setting constructor argument; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSourceLazy': Cannot resolve reference to bean 'dataSourceUnproxied' while setting constructor argument; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSourceUnproxied': Error setting property values; nested exception is org.springframework.beans.PropertyBatchUpdateException; nested PropertyAccessExceptions (1) are:
PropertyAccessException 1: org.springframework.beans.MethodInvocationException: Property 'driverClassName' threw exception; nested exception is java.lang.IllegalStateException: Could not load JDBC driver class [org.postgresql.Driver]
    Line | Method
->>  334 | innerRun  in java.util.concurrent.FutureTask$Sync
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
|    166 | run       in java.util.concurrent.FutureTask
|   1110 | runWorker in java.util.concurrent.ThreadPoolExecutor
|    603 | run       in java.util.concurrent.ThreadPoolExecutor$Worker
^    722 | run . . . in java.lang.Thread
Caused by BeanCreationException: Error creating bean with name 'transactionManager': Cannot resolve reference to bean 'sessionFactory' while setting bean property 'sessionFactory'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sessionFactory': Cannot resolve reference to bean 'dataSource' while setting bean property 'dataSource'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource': Cannot resolve reference to bean 'dataSourceLazy' while setting constructor argument; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSourceLazy': Cannot resolve reference to bean 'dataSourceUnproxied' while setting constructor argument; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSourceUnproxied': Error setting property values; nested exception is org.springframework.beans.PropertyBatchUpdateException; nested PropertyAccessExceptions (1) are:
PropertyAccessException 1: org.springframework.beans.MethodInvocationException: Property 'driverClassName' threw exception; nested exception is java.lang.IllegalStateException: Could not load JDBC driver class [org.postgresql.Driver]
->>  334 | innerRun  in java.util.concurrent.FutureTask$Sync
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
|    166 | run       in java.util.concurrent.FutureTask
|   1110 | runWorker in java.util.concurrent.ThreadPoolExecutor
|    603 | run       in java.util.concurrent.ThreadPoolExecutor$Worker
^    722 | run . . . in java.lang.Thread

まだまだ続くので省略

この場合、まずはPostgreSQLへ接続する為の情報（ユーザ名やパスワード、URLなど）を確認します。
そこに問題が無いようなら、grails cleanでキャッシュ等を一旦全てクリアし、Grailsのインタラクティブモードに入っているのなら一旦抜けてから、再度grails run-appすれば解決します。