gotchas...

gotchas.md

GOTCHAS!

Notes

class B { static belongsTo = A } defines the cascading behaviour from A to B.

When domain B belongsTo A, saves and deletes from A cascade to B. Operations are cascaded from A to B but not from B to A.

class A { static hasMany = [bs:B] } defines a one-to-many relationship, a collection and a cascading behaviour from A to B.

many-to-one

---

class Author {
  String name
  Location location
}

class Location {
  String description
}

• Unidirectional
• Mapped with a foreign key create table author(location_id bigint not null)
• Inserts are not cascaded
• Dirty-checking still applies (Author.get(2).location.description = 'other')
• Can't delete the location
• Deletes are not cascaded

---

class Author {
  String name
  Location location
}

class Location {
  String description
  static belongsTo = Author
}

• Unidirectional
• Mapped with a foreign key create table author(location_id bigint not null)
• Inserts are cascaded
• Dirty-checking still applies (Author.get(2).location.description = 'other')
• Can't delete the location
• Deletes are cascaded
• When many Authors for one Location, deleting an Author deletes the author row but throws an exception when trying to delete Location row... (why did the first delete succeed?)

---

class Author {
  String name
  Location location
}

class Location {
  String description
  static belongsTo = [ author: Author ]
}

• Does not work properly. When trying to fetch Location, tries to find matching author, finds more than one and fails... Author needs static constraint = { location unique: true }

---

one-to-many

class Author {
  String name
  static hasMany = [ books: Book ]
}

class Book {
  String title
}

• Unidirectional
• Mapped with a join table
• Saves on Author are cascaded to Books.
• Clearing the book collection does not delete Books
• Deleting an Author does not delete related Books

---

class Author {
  String name
  static hasMany = [ books: Book ]
}

class Book {
  String title
  static belongsTo = Author
}

• Unidirectional
• Mapped with a join table
• Saves on Author are cascaded to Books.
• Clearing the book collection does not delete Books
• Deleting an Author deletes all related Books

---

class Author {
  String name
  static hasMany = [ books: Book ]
}

class Book {
  String title
  static belongsTo = [ author: Author ]
}

• Bidirectional
• Mapped with a foreign key create table book(author_id bigint not null)
• Saves on Author are cascaded to Books.
• Clearing the book collection does not delete Books
• Deleting an Author deletes all related Books

---

class Author {
  String name
  static hasMany = [ books: Book ]
  static mapping = {
    books cascade: 'all-delete-orphan'
  }
}

class Book {
  String title
}

• Unidirectional
• Mapped with a join table
• Saves on Author are cascaded to Books.
• Clearing the book collection deletes Books
• Deleting an Author deletes all related Books

---

class Author {
  String name
  static hasMany = [ books: Book ]
  static mapping = {
    books cascade: 'all-delete-orphan'
  }
}

class Book {
  String title
  static belongsTo = Author
}

• Unidirectional
• Mapped with a join table
• Saves on Author are cascaded to Books.
• Clearing the book collection deletes Books
• Deleting an Author deletes all related Books

---

class Author {
  String name
  static hasMany = [ books: Book ]
  static mapping = {
    books cascade: 'all-delete-orphan'
  }
}

class Book {
  String title
  static belongsTo = [ author: Author ]
}

• Bidirectional
• Mapped with a foreign key create table book(author_id bigint not null)
• Saves on Author are cascaded to Books.
• Clearing the book collection deletes Books
• Deleting an Author deletes all related Books

---

many-to-many

Mapping lookup data

Fooling around with equals and hashcode

@EqualsAndHashCode
class Location { String description }

• Creating 2 (equal) instances adn saving them stores 2 rows

  @EqualsAndHashCode(includes="description") class Location { String description }

Playing with eager vs lazy

  import gotchas.*

  //def a = new Author(name:'name')
  //100.times { a.addToBooks(new Book(title:'title')) }
  //a.save(flush:true)

  //def all = Author.list()
  def all = Author.list(fetch:[books:'eager'])
  all.each { a ->
    a.books.each { b ->
      print b.title
    }
  }