database - Grails Relation m:n:n -

we work existing mysql database under grails contains m:n relation. no problem here. in situation have add second n relation entry, links same table , has associated first n entry.

if database, create table looks like:

field m_id -> links m table field n_id1 -> links n table field n_id2 -> links n table 

but how can represented in grails domain class?

possibly answer can found somewhere, searches did not successful, maybe due lack of search term creativity.

edit:

trying clarify question: have many-to-many relation, 2 items on 1 side, have maintain association each other (and must clear example original , replacement item), can not seperated 2 separate entries relation.

hmm... try think of racing car drivers nominating series of races, , every nomination has contain driver , substitute. races m (left hand), driver n1 , substitute n2. (it hard work find example...)

edit:

by coincidence found this question addresses same problem left off rather unsolved.

take @ documentation, pretty clear: http://grails.github.io/grails-doc/2.5.0/guide/gorm.html#gormassociation

anyway i'm not sure understand you're trying do, let's try.

if it's one-to-one relation, this:

class domaina {      domainb domainb     domainc firstdomainc     domainc seconddomainc }  class domainb { }  class domainc { } 

that create following fields in "domain_a" table:

• "domain_b_id"
• "first_domain_c_id"
• "second_domain_c_id"

if it's one-to-many relationship domaina both domainb , domainc 2 differentiated collections of domainc in domaina, must have 2 different domaina properties in domainc able map it.

the example airport , flight in documentation:

class airport {     static hasmany = [outboundflights: flight, inboundflights: flight]     static mappedby = [outboundflights: "departureairport",                    inboundflights: "destinationairport"] } class flight {    airport departureairport    airport destinationairport } 

the flight needs airport properties in order able distinguish 1 mapping right hasmany collection in airport.

edit: race-driver example

grails supports many-to-many relations 1 of ends must principal 1 , other must additionally have belongsto it. though not case, since neither race belongs driver nor driver belongs race. use relation property: "drives" property "maindriver". cannot mapped directly, need use domain relation:

class race {     static hasmany = [ participants: driverrace ]      def maindrivers() {         getdrivers( false )     }      def substitutes() {         getdrivers( false )     }      private getdrivers( maindriver ) {         driverrace.withcriteria {             eq( "race", )             eq( "maindriver", maindriver )         }.collect { it.driver }     } }  class driver {     static hasmany = [ races: driverrace ] }  class driverrace {     static belongsto = [ race: race, driver: driver ]      boolean maindriver  }