How to querying across databases with grails? - grails

Question

Is there a way to querying across 2 databases in grails ?
Example (I made a select on two databases - works and test) :
select
c.crf_name,
c.crf_id,
ig.group_id,
ig.group_name,
from
works.crfs c,
test.item_groups ig;
1) I would like to query against two databases, and attach results to a domain.
Or :
2) Is it possible to mixing one query part with data from database and other part with domain class ?
Edit : I need to do a single query mixing tables from 2 databases (one db is PostgreSQL and other db is Mysql). So, in grails is it possible to mix to dataSources beans in one query ?
Edit 2 : Here a better example :
select
igm.item_id,
igm.item_group_id as group_id,
igm.crf_version_id,
ig.name as group_name
from
works.item_group_metadata igm,
test.item_group ig
where
igm.item_group_id=ig.item_group_id
;

Answer 1

If you are planning to do your own sql (like it seems to be the case) over 2 datasources, I suggest that you define your 2 datasources as Spring beans in grails-app/conf/spring.
e.g. (drop your db drivers in /lib and replace the values to match your RDBMS drivers and connection string) :
import org.apache.commons.dbcp.BasicDataSource
import oracle.jdbc.driver.OracleDriver
beans = {
worksDataSource(BasicDataSource) {
driverClassName = "oracle.jdbc.driver.OracleDriver"
url = "jdbc:oracle:thin:#someserver:someport:works"
username = "works"
password = "workspassword"
}
testDataSource(BasicDataSource) {
driverClassName = "oracle.jdbc.driver.OracleDriver"
url = "jdbc:oracle:thin:#someserver:someport:test"
username = "test"
password = "testpassword"
}
}
Then create a service to handle your queries, like :
import groovy.sql.Sql
class SomeService {
def worksDataSource
def testDataSource
def query1 = """
SELECT crf_name, crf_id
FROM works.crfs
"""
def query2 = """
SELECT group_id, group_name
FROM test.item_groups
"""
def sqlWorks = Sql.newInstance(query1)
def sqlTest = Sql.newInstance(query2)
// Then do whatever you like with the results of the 2 queries
// e.g.
sqlWorks.eachRow{ row ->
def someDomainObject = new SomeDomainObject(prop1 : row.crf_name, prop2 : crf_id)
someDomainObject.otherProp = whateverYouLike()
someDomainObject.save()
}
}
Your query doesn't have a where clause so I don't know how you want to relate the data coming from your 2 tables...
If you want to do a single query mixing tables from 2 databases, (ask your DBA to) establish a DBLink between databases test and works and perform the query on the datasource containing the DBLink.
I hope this helps.

Answer 2

You should use a "UNION SELECT" which is supported by most databases. Make sure that both select statements have the same number of columns.
select
crf_name,
crf_id
from
ig
UNION SELECT
group_id,
group_name
from
id
A union select concatenates the results for 2 queries, for example:
select 1 union select 2

Answer 3

Have you looked at the Datasources plugin? It sounds like it will do what you require, but I think you'd need to use HQL or finders on the domain objects directly, rather than SQL, for it to work.
I haven't used the plugin myself but I'd be interested to hear how it goes it you try it.
HTH