Advanced Criteria QueriesWednesday Session - 29th, June

2016

Presented by - Nakul

Agenda

Criteria Queries Overview

Detached Criteria Queries

Named Queries

Audience

Grails Developer

Criteria VS Detached CriteriaCriteria is created based on hibernate session. For example :-

template.getSessionFactory().getCurrentSession().createCriteria(Person.class);

DetachedCriteria is not dependent on hibernate session. For example :-

DetachedCriteria.forClass(Person.class);

Criteria VS Detached Criteria

Criteria Queries require a session to be present when the query is build up and

fired upon database.

Detached Criteria are criteria queries that are not associated with any given

database session/connection.

Detached Criteria queries have many uses including allowing you to create

common reusable criteria queries, execute subqueries and execute batch

updates/deletes.

Building Detached Criteria

import grails.gorm.*

…

def criteria = new DetachedCriteria(Person)

To build a normal criteria query you can use the build closure

def criteria = new DetachedCriteria(Person).build {

eq 'lastName', 'Simpson'

}

Executing Detached Criteria

Unlike regular criteria, Detached Criteria are lazy, in that no query is executed at

the point of definition.

list - List all matching entities

get - Return a single matching result

count - Count all matching records

deleteAll - Delete all matching records

updateAll(Map) - Update all matching records with the given properties

Executing Detached Criteriadef criteria = new DetachedCriteria(Person).build {

ilike 'lastName', 'LastName 2%'

projections{

'lastName'

}

}

def results = criteria.list(max: 8, sort: "lastName")

def results1 = criteria.list(max:8, sort:"lastName") {

gt 'age', 24

}

To retrieve a single result you can use the get or find methods (which are synonyms):

Person p = criteria.find() // or criteria.get()

Executing Detached CriteriaThe DetachedCriteria class itself also implements the Iterable interface

which means that it can be treated like a list:

def criteria = new DetachedCriteria(Person).build {

eq 'lastName', 'LastName 2%'

}

criteria.each {

println it.firstName

}

In this case the query is only executed when the each method is called. The same

applies to all other Groovy collection iteration methods.

Executing Detached CriteriaYou can also execute dynamic finders on DetachedCriteria just like on

domain classes. For example:

def criteria1 = new DetachedCriteria(Person).build {

ilike 'lastName', 'LastName 2%'

}

def person = criteria1.findByAge(76)

Batch Operations with Detached CriteriaThe DetachedCriteria class can be used to execute batch operations such as

batch updates and deletes. For example, the following query will update all people

with the surname "Simpson" to have the surname "Bloggs" -

def criteria = new DetachedCriteria(Person).build {

eq 'lastName', 'Simpson'

}

int total = criteria.updateAll(lastName:"Bloggs")

Batch Operations with Detached CriteriaThe DetachedCriteria class can be used to execute batch operations such as

batch updates and deletes. For example, the following query will update all people

with the surname "Simpson" to have the surname "Bloggs" -

def criteria = new DetachedCriteria(Person).build {

eq 'lastName', 'Simpson'

}

int total = criteria.updateAll(lastName:"Bloggs")

Batch Operations with Detached CriteriaTo batch delete records you can use the deleteAll method

def criteria = new DetachedCriteria(Person).build {

eq 'lastName', 'Nexthoughts'

}

int total = criteria.deleteAll()

Named QueriesThe namedQueries static property defines named queries.

Named queries support the criteria builder syntax.

static namedQueries = {

lastNameFilter {

ilike('lastName', 'Next%')

}

}

Executing Named Queries

// Lists All records from person where lastName ilike “Next%” -

List<Person> personList= Person.lastNameFilter.list()

//Get’s the first element

Person.lastNameFilter.get()

//Get total count of records present

Person.lastNameFilter.count()

Executing Named Queries

//Execute list as we did with criteria

Person.lastNameFilter.list(max: 5)

//Apply more criteria within the namedQuerry

Person.lastNameFilter{ lt ('age',65 as Long)}

References

1. The Definitive Guide to Grails 2 - Graeme Rocher & Jeff Scott Brown

2. Programming Grails - Burt Beckwith

3. Grails Documentation - Detached Criteria

4. http://tatiyants.com/how-and-when-to-use-various-gorm-querying-options/

Questions ?

Thank You !