Grails 2 multiple dynamic datasources in services

Question

I am working on a Grails application where I must access several datasources. The datasources are defined in the default database (ie. they are stored there and I must make

Answer 1

I worked on similar project where the application has to retrieve list of datasources (connection strings) from the default database, and connect to each datasource and perform operations using quartz jobs.

I implemented it like, connect to each datasource within the application (not from DataSorce.groovy) and write SQL rather tahn HQL.

import groovy.sql.Sql

class SqlService{
    Sql getDbConnection(String connectionString, String dbUser, String dbPassword){
        def sql = Sql.newInstance(connectionString, dbUser, dbPassword, "driver_class")
        return sql
    }
}

Get sql connection from the above code and execute SQL queries using sql.execute "SQL STATEMENT" and close the sql connection. Here is the Sql class documentation.

Answer 2

Use sharding plugin for grails that will address your issue

Answer 3

You can add multiple data sources in a single application, and access them in the services.

Firstly you need to add basic data sources in the resources.groovy.

first import BasicDataSource

import org.apache.commons.dbcp.BasicDataSource;

Then

    switch (grails.util.GrailsUtil.environment) {
    case "development":
        firstDataSource( BasicDataSource ) {
            driverClassName = "net.sourceforge.jtds.jdbc.Driver"
            url = "jdbc:jtds:sqlserver://localhost:1433;DatabaseName=<Db_name>"
            username = "sa"
            password = "root"
            String SqlServerInstance = "SQLEXPRESS";
            url = url + ";" + SqlServerInstance;
        }
        break

    case "test":
        firstDataSource( BasicDataSource ) {

            driverClassName = "net.sourceforge.jtds.jdbc.Driver"
            url = "jdbc:jtds:sqlserver://localhost:1433;DatabaseName=<Db_name>"
            username = "sa"
            password = "root"
            String SqlServerInstance = "SQLEXPRESS";
            url = url + ";" + SqlServerInstance;            }
        break;

}

In the same way you can add more data sources, above code will give you one more datasource to access other than the default one. I used switch to configure same data source for the different environments, same way more can be added.

and in the service it can be accessed in the services as:

BasicDataSource firstDataSource;
Connection con = firstDataSource.getConnection();

and then connection object can be used.

I think it should help

Answer 4

I've got two different datasources working with Grails 2.3.11. I'm using 1 datasource for my H2 database and another for an Oracle db. I had to use Hibernate 4 with Grails 2.3. In my BuildConfig.groovy I specified the dependency on hibernate 4:

runtime ":hibernate4:4.3.5.4"

In my DataSource.groovy file I used the following Hibernate caching settings:

hibernate {
    cache.use_second_level_cache = true
    cache.use_query_cache = false
    cache.region.factory_class = 'org.hibernate.cache.ehcache.SingletonEhCacheRegionFactory'
    singleSession = true // configure OSIV singleSession mode
}

(SIDE NOTE: without the cache settings, I was getting following CacheManager error, "Another unnamed CacheManager already exists in the same VM". There's an open bug report on this at https://jira.grails.org/browse/GPCACHEEHCACHE-13, but once I put the settings in place the error was gone.)

then I defined my datasources:

environments {
    development {
        dataSource_oracle {
            pooled = true
            dialect = org.hibernate.dialect.Oracle10gDialect
            driverClassName = 'oracle.jdbc.OracleDriver'
            username = 'user'
            password = 'pass'
            url = 'jdbc:oracle:thin:@(serverName):(port):(SID)'
            dbCreate = 'validate'
        }
        dataSource {
            dbCreate = "update"
            url = "jdbc:h2:devDb;MVCC=TRUE;LOCK_TIMEOUT=10000;DB_CLOSE_ON_EXIT=FALSE"
            properties {
               jmxEnabled = true
               initialSize = 5
               maxActive = 50
               minIdle = 5
               maxIdle = 25
               maxWait = 10000
               maxAge = 10 * 60000
               timeBetweenEvictionRunsMillis = 5000
               minEvictableIdleTimeMillis = 60000
               validationQuery = "SELECT 1"
               validationQueryTimeout = 3
               validationInterval = 15000
               testOnBorrow = true
               testWhileIdle = true
               testOnReturn = false
               jdbcInterceptors = "ConnectionState"
               defaultTransactionIsolation = java.sql.Connection.TRANSACTION_READ_COMMITTED
            }
        }
    }
}

By default, my Domain classes use the H2 db and I specify my Oracle datasource as:

class MyService {

    def dataSource_oracle
    static transactional = true

    def getMethod() {
        assert dataSource_oracle != null, "dataSource is null! Please check your configuration!"
        def sql = Sql.newInstance(dataSource_oracle)
        ...
    }
}

Above, I allow the dependency injection to provide the service with the oracle datasource, def dataSource_oracle. If I want to use the H2 datasource, I declare the datasource as def dataSource and allow the DI to inject my other datasource.

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I could not get the two datasources to work as specified in the documentation at http://grails.github.io/grails-doc/2.3.11/guide/conf.html#multipleDatasources. By declaring the datasources as dataSource and dataSource_lookup then using it as:

class DataService {
   static datasource = 'lookup'

   void someMethod(...) {
      …
   }
} 

but I was able to get it working with the solution described above.

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