mysql - Grails Database Mapping -

my problem database mapping , don't working. i've done this tutorial.

class comment { string comment date datecreated // predefined names grails filled automatically date lastupdated // predefined names grails filled automatically  user user  // delete comment feedback if feedback item deleted  static belongsto=[feedback:feedback]  static mapping = {     feedback column: 'comment_feedback_id', jointable: false }  static constraints = {     comment (blank:false, nullable: false, size:5..500)     user (nullable: true) // comments allowed without user }   string tostring(){     if (comment?.size()>20){         return comment.substring(0,19);     } else         return comment; }}  class feedback { string title string feedback date datecreated // predefined names grails filled automatically date lastupdated // predefined names grails filled automatically  // relationship other classes user user   static hasmany=[comments:comment]  static mapping = {     comments column: 'feedback_comment_id', jointable: false }  // constrains defined static static constraints ={     title(blank:false, nullable: false, size:3..80)     feedback(blank:false, nullable:false, size:3..500)     user(nullable:false) }}  class user { string name string email string webpage   static constraints = {     name (blank:false, nullable:false, size:3..30, matches:"[a-za-z1-9_]+")     email (email:true)     webpage (url:true) }  string tostring(){     return name; } } 

when try delete user connected feedback/ comment, error:

cannot delete or update parent row: foreign key constraint fails (guestbook.comment, constraint fk_mxoojfj9tmy8088avf57mpm02 foreign key (user_id) references user (id))

what should mapping like?

you have multiple problems domain design, first remove user comment ,as user have comment feedback. if still wish keep design, define belongsto user,in both comment , feedback.

try this...

add hasone feedback user

class user { string name string email string webpage  hasone = [feedback:feedback ] static constraints = {     name (blank:false, nullable:false, size:3..30, matches:"[a-za-z1-9_]+")     email (email:true)     webpage (url:true) }  string tostring(){     return name; } } 

add feedback belongsto user , cascade on delete comment

class feedback { string title string feedback date datecreated // predefined names grails filled automatically date lastupdated // predefined names grails filled automatically  // relationship other classes user user static belongsto = [user]  static hasmany=[comments:comment]  static mapping = {     comments cascade: 'all-delete-orphan',column: 'feedback_comment_id', jointable: false }  // constrains defined static static constraints ={     title(blank:false, nullable: false, size:3..80)     feedback(blank:false, nullable:false, size:3..500)     user(nullable:false) }} 

simply remove user comment

class comment { string comment date datecreated // predefined names grails filled automatically date lastupdated // predefined names grails filled automatically  //user user  // delete comment feedback if feedback item deleted  /static belongsto=[user,feedback:feedback] static belongsto=[feedback:feedback]  static mapping = {     feedback column: 'comment_feedback_id', jointable: false }  static constraints = {     comment (blank:false, nullable: false, size:5..500)     //user (nullable: true) // comments allowed without user }   string tostring(){     if (comment?.size()>20){         return comment.substring(0,19);     } else         return comment; }}