ruby - DataMapper Many-to-Many Delete Constraint -

let's have 2 models many-to-many relation:

class tag   include datamapper::resource   property :id, serial   has n, :articles, through: resource end  class article   include datamapper::resource   property :id, serial   has n, :tags, through: resource end 

now if create article tag: tag.create(articles: [ article.create ])

if run tag.first.delete now, returns false since there foreign key constraint due many-to-many relationship. if run tag.first.delete! deletes tag not association record in article_tags table.

if use dm-contraints , set :destroy destroys article not want.

i can do

tag = tag.first tag.articles = [] tag.save tag.destroy 

but seems seems unclean. there better way?

since tag , article linked through many-to-many relationship, you'll need first destroy 'articletag' join model references object you're trying delete.

#get tag delete tag = tag.first  #deletes rows in article_tags table reference #the tag want delete articletag.all(:tag => tag).destroy  #an alternative line above--it same thing tag.article_tags.all.destroy  #another alternative--it won't delete articles #the join model references tag tag.articles.all.destroy  #finally, obliterate tag tag.destroy