Grails sql queries - sql

Question

Imagine I have something like this:
def example = {
def temp = ConferenceUser.findAllByUser(User.get(session.user))
[temp: temp]
}
Explaining my problem:
Although dynamic finders are very easy to use and fast to learn, I must replace dynamic finders of my website for sql queries because it is a requirement. As I don't understand SQL that much, my main questions are:
a) I am using an SQLS database, with the drivers and datasource good configured and my website works as it is right now. If I want to replace the "findAllByUser" for an sql statement, should i do something like this:
def dataSource
...
def db = new Sql(dataSource)
def temp = db.rows("SELECT ... ")
b) And that will work? I mean, the temp object will be a list as it is if I use "findAllByUser", and do I need to open a connection to the database =?

Answer 1

With Grails you can use Dynamic Finders, Criteria Builders, Hibernate Query Language (HQL), or Groovy SQL.
To use Groovy SQL:
import groovy.sql.Sql
Request a reference to the datasource with def dataSource or def sessionFactory for transactions
Create an Sql object using def sql = new Sql(dataSource) or def sql = new Sql(sessionFactory.currentSession.connection())
Use Groovy SQL as required
Grails will manage the connection to the datasource automatically.
Sql.rows returns a list that can be passed to your view.
For example:
import groovy.sql.Sql
class MyController {
def dataSource
def example = {
def sql = new Sql(dataSource)
[ temp: sql.rows("SELECT . . .") ]
}
}
And within a transaction:
import groovy.sql.Sql
class MyController {
def sessionFactory
def example = {
def sql = new Sql(sessionFactory.currentSession.connection())
[ temp: sql.rows("SELECT . . .") ]
}
}
I recommend the book Grails Persistence with GORM and GSQL for a lot of great tips and techniques.

Answer 2

yes, with grails you can do both plain sql and hql queries. HQL is 'hibernate query language' and allows you to write sql-like statements, but use your domain classes and properties instead of the table names and column names. To do an hql query, do something like
def UserList = ConferenceUser.executeQuery('from ConferenceUser cu where cu.user = ?', [user]),
what you have here is a parameterized query -- executeQuery sees the ? in the hql string and substitutes the arguments in the array that is the second parameter to the method([user] in this case) for you.
See
http://grails.org/doc/latest/ref/Domain%20Classes/executeQuery.html
and you can see this on how to do sql queries with Grails
Sql query for insert in grails

Answer 3

Going Further / Tips
Use Spring beans
You can make the groovy.sql.Sql instance a Spring bean in your Grails application. In grails-app/conf/spring/resources.groovy define the Sql bean:
// File: grails-app/conf/spring/resources.groovy
beans = {
// Create Spring bean for Groovy SQL.
// groovySql is the name of the bean and can be used
// for injection.
sql(groovy.sql.Sql, ref('dataSource'))
}
Next inject the Sql instance in your your class.
package com.example
import groovy.sql.GroovyRowResult
class CarService {
// Reference to sql defined in resources.groovy.
def sql
List<GroovyRowResult> allCars(final String searchQuery) {
final String searchString = "%${searchQuery.toUpperCase()}%"
final String query = '''\
select id, make, model
from car
where ...
'''
// Use groovySql bean to execute the query.
final results = sql.rows(query, search: searchString)
results
}
}
Multiple Datasources
adminSql(groovy.sql.Sql, ref("dataSource_admin"))
userSql(groovy.sql.Sql, ref("dataSource_user"))
and inject the beans
def userSql
def adminSql
Into the services that need them.
or without injection
import groovy.sql.Sql
// ...
// inject the datasource bean
def dataSource_admin
// ...
// in a method
Sql sql = new Sql(dataSource_admin)
Early Grails Version
Looping through GORM result sets in early grails versions can cause needless queries in the middle of template loops. Using groovy SQL can help with this.