Grails run query postgresql on second database to generate Raw JSON - json

Question

I have one postgreSQL database which I am using inside my Grails application(configured in Datasource.groovy), lets call it DB1. Now I have other postgreSQL database which has lots of data inside it, lets call it DB2.
I am writing an data export procedure which takes in JSON data generated from DB2, make its domain objects and store it inside the DB1. This data is being sent from another software using DB2. The main problem is that both databases have different column names so it cannot be a direct import export.
PostgreSQL provides direct methods to generate JSON via SQL queries. Eg-
SELECT row_to_json(t)
FROM ( select id, descrizione as description from tableXYZ ) t
It returns a JSON output-
{"id":6013,"description":"TestABC"}
This JSON can be consumed by the code that I have made.
So I want to run this query on DB2 from inside grails application which has DB1 configured inside Datasource.groovy.
How to do that?

Answer 1

In your DataSource.groovy file, you need to create another data source to point at DB2. You can probably clone your dataSource definition for this, eg.
http://grails.github.io/grails-doc/2.3.9/guide/conf.html#multipleDatasources
dataSource_db2 {
pooled = true
jmxExport = true
driverClassName = "org.postgresql.Driver"
username = "XXX"
password = "YYY"
//noinspection GrReassignedInClosureLocalVar
dialect = PostgreSQLDialect
autoreconnect = true
useUnicode = true
characterEncoding = "utf-8"
tcpKeepAlive = true
//noinspection GroovyAssignabilityCheck
properties {
// See http://grails.org/doc/latest/guide/conf.html#dataSource for documentation
initialSize = 5
maxActive = 50
minIdle = 5
maxIdle = 25
maxWait = 10000
maxAge = 10 * 60000
timeBetweenEvictionRunsMillis = 1000 * 60 * 1 // 1 min
minEvictableIdleTimeMillis = 1000 * 60 * 5 // 5 min
numTestsPerEvictionRun = 3
validationQuery = 'SELECT 1'
validationQueryTimeout = 3
validationInterval = 15000
testOnBorrow = true
testWhileIdle = false
testOnReturn = false
defaultTransactionIsolation = Connection.TRANSACTION_READ_COMMITTED
removeAbandoned = true
removeAbandonedTimeout = 20 // 20s is a long query
logAbandoned = true // causes stacktrace recording overhead, use only for debugging
// use JMX console to change this setting at runtime
// the next options are jdbc-pool specific
// http://tomcat.apache.org/tomcat-7.0-doc/jdbc-pool.html#Common_Attributes
// https://tomcat.apache.org/tomcat-7.0-doc/api/org/apache/tomcat/jdbc/pool/PoolConfiguration.html
jmxEnabled = true
// ResetAbandonedTimer resets the timer upon every operation on the connection or a statement.
// ConnectionState caches the auto commit, read only and catalog settings to avoid round trips to the DB.
jdbcInterceptors = "ConnectionState;ResetAbandonedTimer;SlowQueryReportJmx(threshold=10000)"
abandonWhenPercentageFull = 25 // settings are active only when pool is full
}
}
To use it for database connection access, you can inject the javax.sql.DataSource into your Services, Controllers, Domain classes, or other Grails Artefakts.
eg.
import javax.sql.DataSource
import groovy.sql.GroovyResultSet
import groovy.sql.Sql
MyService {
DataSource dataSource_db2
def doQuery(String query) {
new Sql(dataSource_db2).rows(query)
}
}
To have a domain object use your db2 dataSource for GORM, add to your domain objects 'mapping' block:
static mapping = {
datasource 'db2'
}
If you want JNDI support, you can also add something like this in your resources.groovy:
xmlns jee: "http://www.springframework.org/schema/jee"
jee.'jndi-lookup'(id: "dataSource", 'jndi-name': "java:comp/env/jdbc/db1")
jee.'jndi-lookup'(id: "dataSource_db2", 'jndi-name': "java:comp/env/jdbc/db2")