Relationships Between Domain Classes Grails

Relationships Between Domain Classes     Grails main page

• There are two static variables that define relationships between domain classes: 
• belongsTo  
• hasMany
  
• For example, if there is a class Company, and there are many Employees in a Company, you say the following:
• Put this in the Company class
• static hasMany = [employees: Employee]
• Put this in the Employee class:
• static belongsTo = Company
• Company company
• As mentioned before, constraints tell the order that fields get displayed.  So in the in the Company class you would say:
  
  static constraints = {
                  ....
                  employees()
                  ....
  }
• The belongsTo also tells Grails that the Employee instance is owned by the Company instance, so that when a Company is deleted, all Employees are automatically deleted also.
• Using these two static declarations, you can describe the following relationships.
  
  one-to-many
  many-to-one
  one-to-one