Grails(5)Guide Book Chapter 6 GORM

Grails(5)GuideBookChapter6GORM

6.3PersistenceBasics

6.3.1SavingandUpdating

defp=Person.get(1)

p.save()

Thissavewillbenotbepushedtothedatabaseimmediately.Itwillbepushedwhenthenextflushoccurs.

try{

p.save(flush:true)//Flushimmediately.

}catch(org.springframework.dao.DataIntegrityViolationExceptione){

}

Grailsvalidatesadomaininstanceeverytimewhenwesaveit.

try{

p.save(failOnError:true)

}catch{}

6.3.2DeletingObjects

defp=Person.get(1)

p.delete()

Almostthesaveasduringsaving

try{

p.delete(flush:true)

}catch(org.springframework.dao.DataIntegrityViolationExceptione){}

Ifweneedbatchdeletingfunction,weuseexecuteUpdate

Customer.executeUpdate("deleteCustomercwherec.name=ldName",

[oldName:"Carl"])

6.3.3UnderstandingCascadingUpdatesandDeletes

6.3.4EagerandLazyFetching

Defaultarelazyfetching

ConfiguringEagerFetching

classAirport{

Stringname

statichasMany=[flights:Flight]

staticmapping={

flightslazy:false

}

}

UsingBatchFetching

Ifweuseeagerfetchallthetimeforallthedata,itwillresultsomeperformanceandmemoryproblems.

classAirport{

Stringname

statichasMany=[flights:Flight]

staticmapping={

flightsbatchSize:10

}

}

Or

classFlight{

…

staticmapping={

batchSize10

}

}

6.3.5PessimisticandOptimisticLocking

defairport=Airport.lock(10)

6.3.6ModificationChecking

isDirty

Wecanusethismethodtocheckifanyfieldhasbeenmodified.

defairport=Airport.get(10)

assert!airport.isDirty()

airport.properties=params

if(airport.isDirty()){

...

}

Wecanalsocheckifindividualfieldshavebeenmodified.

defairport=Airport.get(10)

assert!airport.isDirty()

airport.properties=params

if(airport.isDirty('name')){

…snip...

}

getDirtyPropertyNames

Wecanusethismethodtoretrievethenamesofmodifiedfields.

defairport=Airport.get(10)

assert!airport.isDirty()

airport.properties=params

defmodifiedFieldNames=airport.getDirtyPropertyNames()

for(fieldNameinmodifiedFieldNames){

…snip...

}

getPersistentValue

Wecanalsousethismethodtoretrievethevalueofamodifiedfield.

defairport=Airport.get(10)

assert!airport.isDirty()

airport.properties=params

defmodifiedFieldNames=airport.getDirtyPropertyNames()

for(fieldNameinmodifiedFieldNames){

defcurrentValue=airport."$fieldName"

deforiginalValue=airport.getPersistentValue(fieldName)

if(currentValue!=originalValue){

…snip...

}

}

6.4QueryingwithGORM

DynamicFinders

WhereQueries

CriteriaQueries

HibernateQueryLanguage(HQL)

ListingInstances

defbooks=Book.list()

defbooks=Book.list(offset:10,max:20)//pagination

defbooks=Book.list(sort:"title",order:"asc")//sort

RetrievalbyDatabaseIdentifier

defbook=Book.get(23)

defbooks=Book.getAll(23,93,81)

6.4.1DynamicFinders

classBook{

Stringtitle

DatereleaseDate

Authorauthor

}

classAuthor{

Stringname

}

defbook=Book.findByTitle("ThePython")

book=Book.findByTitleLike("Python%")

book=Book.findByReleaseDateBetween(firstDate,secondDate)

book=Book.findByReleaseDateGreaterThan(someDate)

book=Book.findByTitleLikeOrReleaseDateLessThan("%Python%",someDate)

MethodExpressions

InList,LessThan,LessThanEquals,GreaterThan,GreaterThanEquals

Like,

Ilike-similartoLike,exceptcaseinsensitive

NotEqual,Between,IsNotNull,IsNull

Booleanlogic(AND/OR)

defbooks=Book.findAllByTitleLikeAndReleaseDateGreaterThan(

“%Java%”,newDate()-30)

QueryingAssociations

PaginationandSorting

6.4.2WhereQueries

BasicQuerying

defquery=Person.where{

firstName=="Carl"

}

Personcarl=query.find()

Personp=Person.find{firstName=="Carl"}

defresults=Person.findAll{

lastName=="Luo"

}

==eq

!=ne

>gt

<lt

>=ge

<=le

ininList

==~like

=~ilike

defquery=Person.where{

(lastName!="Carl"&&firstName!="Book")||(firstName=="Carl"&&age>9)

}

defresults=query.list(sort:"firstName")

QueryComposition

Conjunction,DisjunctionandNegation

…snip…

6.4.3Criteria

6.4.4DetachedCriteria

6.4.5HibernateQueryLanguage(HQL)

defresults=

Book.findAll("fromBookasbwhereb.titlelike'Lordofthe%'")

PositionalandNamedParameters

defresults=

Book.findAll("fromBookasbwhereb.titlelike?",["TheShi%"])

Ornamedparameters

defbooks=Book.findAll("fromBookasbookwherebook.author=:author",

[author:author])

PaginationandSorting

defresults=

Book.findAll("fromBookasbwhere"+

"b.titlelike'Lordofthe%'"+

"orderbyb.titlesac",

[max:10,offset:20])

6.5AdvancedGORMFeatures

6.5.1EventsandAutoTimestamping

EventTypes

ThebeforeInsertevent

Firedbeforeanobjectissavedtothedatabase

classPerson{

privatestaticfinalDateNULL_DATE=newDate(0)

StringfirstName

StringlastName

DatesignupDate=NULL_DATE

defbeforeInsert(){

if(signupDate==NULL_DATE){

signupDate=newDate()

}

}

}

ThebeforeUpdateevent

Firedbeforeanexistingobjectisupdated

classPerson{

defsecurityService

StringfirstName

StringlastName

StringlastUpdateBy

staticconstraints={

lastUpdatedBynullable:true

}

defbeforeUpdate(){

lastUpdateBy=securityService.currentAuthenticatedUsername()

}

}

ThebeforeDeleteevent

Firedbeforeanobjectisdeleted.

classPerson{

Stringname

defbeforeDelete(){

ActivityTrace.withNewSession{

newActivityTrace(eventName:"PersonDeleted",data:name).save()

}

}

}

ThebeforeValidateevent

Firedbeforeanobjectisvalidated.

classPerson{

Stringname

staticconstraints={

namesize:5..45

}

defbeforeValidate(){

name=name?.trim()

}

}

TheonLoad/beforeLoadevent

classPerson{

Stringname

DatedateCreated

DatelastUpdated

defonLoad(){

log.debug"Loading${id}"

}

}

TheafterLoadevent

Firedimmediatelyafteranobjectisloadedfromthedatabase:

classPerson{

Stringname

DatedateCreated

DatelastUpdated

defafterLoad(){

name="I'mloaded"

}

}

CustomEventListeners

6.5.2CustomORMMapping

6.5.2.1TableandColumnNames

6.5.2.2CachingStrategy

Settingupcaching

configuredinthegrails-app/conf/DateSource.groovy

hibernate{

cache.use_second_level_cache=true

cache.use_query_cache=true

cache.provider_class='org.hibernate.cache.EhCacheProvider'

}

6.5.2.3InheritanceStrategies

6.5.2.4CustomDatabaseIdentity

6.5.2.9CustomCascadeBehaviour

…snip...

References:

http://grails.org/doc/latest/guide/GORM.html#persistenceBasics

http://grails.org/doc/latest/guide/index.html