Doctrine2 Best way to handle many-to-many with extra columns in reference table

Question

I m wondering what s the best  the cleanest and the most simply way to work with many-to-many relations in Doctrine2    Let s assume that we ve got an album like Master of Puppets by Metallica with several tracks  But please note the fact that one track might appears in more that one album  like Battery by Metallica does - three albums are featuring this track   So what I need is many-to-many relationship between albums and tracks  using third table with some additional columns  like position of the track in specified album   Actually I have to use  as Doctrine s documentation suggests  a double one-to-many relation to achieve that functionality        Entity      class Album            Id  Column type  integer          protected  id            Column          protected  title            OneToMany targetEntity  AlbumTrackReference   mappedBy  album          protected  tracklist       public function   construct              this- gt tracklist   new  Doctrine Common Collections ArrayCollection               public function getTitle             return  this- gt title             public function getTracklist             return  this- gt tracklist- gt toArray                  Entity      class Track            Id  Column type  integer          protected  id            Column          protected  title            Column type  time          protected  duration            OneToMany targetEntity  AlbumTrackReference   mappedBy  track          protected  albumsFeaturingThisTrack     btw  any idea how to name this relation          public function getTitle             return  this- gt title             public function getDuration             return  this- gt duration                Entity      class AlbumTrackReference            Id  Column type  integer          protected  id            ManyToOne targetEntity  Album   inversedBy  tracklist          protected  album            ManyToOne targetEntity  Track   inversedBy  albumsFeaturingThisTrack          protected  track            Column type  integer          protected  position            Column type  boolean          protected  isPromoted       public function getPosition             return  this- gt position             public function isPromoted             return  this- gt isPromoted             public function getAlbum             return  this- gt album             public function getTrack             return  this- gt track            Sample data                Album  ---- --------------------------    id   title                       ---- --------------------------     1   Master of Puppets             2   The Metallica Collection    ---- --------------------------                  Track  ---- ---------------------- ----------    id   title                  duration    ---- ---------------------- ----------     1   Battery                00 05 13      2   Nothing Else Matters   00 06 29      3   Damage Inc             00 05 33    ---- ---------------------- ----------                 AlbumTrackReference  ---- ---------- ---------- ---------- ------------    id   album id   track id   position   isPromoted    ---- ---------- ---------- ---------- ------------     1          1          2          2            1      2          1          3          1            0      3          1          1          3            0      4          2          2          1            0    ---- ---------- ---------- ---------- ------------    Now I can display a list of albums and tracks associated to them    dql         SELECT   a  tl  t     FROM     Entity Album a     JOIN     a tracklist tl     JOIN     tl track t     ORDER BY tl position ASC      albums    em- gt createQuery  dql - gt getResult     foreach   albums as  album        echo  album- gt getTitle     PHP EOL       foreach   album- gt getTracklist   as  track            echo sprintf   t  d -  -20s   s   s n                 track- gt getPosition                 track- gt getTrack  - gt getTitle                 track- gt getTrack  - gt getDuration  - gt format  H i s                 track- gt isPromoted       - PROMOTED                                The results are what I m expecting  ie  a list of albums with their tracks in appropriate order and promoted ones being marked as promoted   The Metallica Collection      1 - Nothing Else Matters  00 06 29   Master of Puppets      1 - Damage Inc            00 05 33        2 - Nothing Else Matters  00 06 29   - PROMOTED       3 - Battery               00 05 13     So what s wrong   This code demonstrates what s wrong   foreach   album- gt getTracklist   as  track        echo  track- gt getTrack  - gt getTitle        Album  getTracklist   returns an array of AlbumTrackReference objects instead of Track objects  I can t create proxy methods cause what if both  Album and Track would have getTitle   method  I could do some extra processing within Album  getTracklist   method but what s the most simply way to do that  Am I forced do write something like that   public function getTracklist          tracklist   array         foreach   this- gt tracklist as  key   gt   trackReference             tracklist  key     trackReference- gt getTrack              tracklist  key - gt setPosition  trackReference- gt getPosition              tracklist  key - gt setPromoted  trackReference- gt isPromoted                return  tracklist        And some extra getters setters in Track class   EDIT   beberlei suggested to use proxy methods   class AlbumTrackReference       public function getTitle             return  this- gt getTrack  - gt getTitle             That would be a good idea but I m using that  reference object  from both sides   album- gt getTracklist   12 - gt getTitle   and  track- gt getAlbums   1 - gt getTitle    so getTitle   method should return different data based on the context of invocation   I would have to do something like    getTracklist          foreach   this- gt tracklist as  trackRef     trackRef- gt setContext  this                    getAlbums          foreach   this- gt tracklist as  trackRef     trackRef- gt setContext  this                   AlbumTrackRef  getTitle           return  this- gt   this- gt context - gt getTitle         And that s not a very clean way

User · Answer

First  I mostly agree with beberlei on his suggestions   However  you may be designing yourself into a trap   Your domain appears to be considering the title to be the natural key for a track  which is likely the case for 99  of the scenarios you come across   However  what if Battery on Master of the Puppets is a different version  different length  live  acoustic  remix  remastered  etc  than the version on The Metallica Collection   Depending on how you want to handle  or ignore  that case  you could either go beberlei s suggested route  or just go with your proposed extra logic in Album  getTracklist     Personally  I think the extra logic is justified to keep your API clean  but both have their merit   If you do wish to accommodate my use case  you could have Tracks contain a self referencing OneToMany to other Tracks  possibly  similarTracks   In this case  there would be two entities for the track Battery  one for The Metallica Collection and one for Master of the Puppets   Then each similar Track entity would contain a reference to each other   Also  that would get rid of the current AlbumTrackReference class and eliminate your current  issue    I do agree that it is just moving the complexity to a different point  but it is able to handle a usecase it wasn t previously able to

User · Answer

Here is the solution as described in the Doctrine2 Documentation   lt  php use Doctrine Common Collections ArrayCollection        Entity    class Order            Id  Column type  integer    GeneratedValue        private  id            ManyToOne targetEntity  Customer          private  customer           OneToMany targetEntity  OrderItem   mappedBy  order          private  items            Column type  boolean          private  payed   false           Column type  boolean          private  shipped   false           Column type  datetime          private  created       public function   construct Customer  customer                 this- gt customer    customer           this- gt items   new ArrayCollection             this- gt created   new  DateTime  now                  Entity    class Product            Id  Column type  integer    GeneratedValue        private  id            Column type  string          private  name            Column type  decimal          private  currentPrice       public function getCurrentPrice                 return  this- gt currentPrice                Entity    class OrderItem            Id  ManyToOne targetEntity  Order          private  order            Id  ManyToOne targetEntity  Product          private  product            Column type  integer          private  amount   1            Column type  decimal          private  offeredPrice       public function   construct Order  order  Product  product   amount   1                 this- gt order    order           this- gt product    product           this- gt offeredPrice    product- gt getCurrentPrice

User · Answer

I ve opened a similar question in the Doctrine user mailing list and got a really simple answer   consider the many to many relation as an entity itself  and then you realize you have 3 objects  linked between them with a one-to-many and many-to-one relation   http   groups google com group doctrine-user browse thread thread d1d87c96052e76f7 436b896e83c10868 436b896e83c10868  Once a relation has data  it s no more a relation

User · Answer

The solution is in the documentation of Doctrine  In the FAQ you can see this    http   docs doctrine-project org en 2 1 reference faq html how-can-i-add-columns-to-a-many-to-many-table  And the tutorial is here    http   docs doctrine-project org en 2 1 tutorials composite-primary-keys html  So you do not anymore do a manyToMany but you have to create an extra Entity and put manyToOne to your two entities   ADD for  f00bar comment    it s simple  you have just to to do something like this     Article  1--N  ArticleTag  N--1  Tag   So you create an entity ArticleTag  ArticleTag    type  entity   id      id        type  integer       generator          strategy  AUTO   manyToOne      article        targetEntity  Article       inversedBy  articleTags   fields         your extra fields here   manyToOne      tag        targetEntity  Tag       inversedBy  articleTags   I hope it helps

User · Answer

Nothing beats a nice example  For people looking for a clean coding example of an one-to-many many-to-one associations between the 3 participating classes to store extra attributes in the relation check this site out   nice example of one-to-many many-to-one associations between the 3 participating classes  Think about your primary keys  Also think about your primary key  You can often use composite keys for relationships like this  Doctrine natively supports this  You can make your referenced entities into ids  Check the documentation on composite keys here

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I was getting from a conflict with join table defined in an association class   with additional custom fields   annotation and a join table defined in a many-to-many annotation   The mapping definitions in two entities with a direct many-to-many relationship appeared to result in the automatic creation of the join table using the  joinTable  annotation  However the join table was already defined by an annotation in its underlying entity class and I wanted it to use this association entity class s own field definitions so as to extend the join table with additional custom fields   The explanation and solution is that identified by FMaz008 above  In my situation  it was thanks to this post in the forum  Doctrine Annotation Question   This post draws attention to the Doctrine documentation regarding ManyToMany Uni-directional relationships  Look at the note regarding the approach of using an  association entity class  thus replacing the many-to-many annotation mapping directly between two main entity classes with a one-to-many annotation in the main entity classes and two  many-to-one  annotations in the associative entity class  There is an example provided in this forum post Association models with extra fields   public class Person           OneToMany targetEntity  AssignedItems   mappedBy  person        private  assignedItems      public class Items             OneToMany targetEntity  AssignedItems   mappedBy  item          private  assignedPeople     public class AssignedItems             ManyToOne targetEntity  Person          JoinColumn name  person id   referencedColumnName  id          private  person            ManyToOne targetEntity  Item          JoinColumn name  item id   referencedColumnName  id          private  item

User · Answer

While getting all album tracks form inside album class  you ll generate one more query for one more record  That s because of proxy method  There s another example of my code  see last post in topic   http   groups google com group doctrine-user browse thread thread d1d87c96052e76f7 436b896e83c10868 436b896e83c10868  Is there any other method to resolve that  Isn t a single join a better solution

User · Answer

You may be able to achieve what you want with Class Table Inheritance where you change AlbumTrackReference to AlbumTrack   class AlbumTrack extends Track                 And getTrackList   would contain AlbumTrack objects which you could then use like you want   foreach  album- gt getTrackList   as  albumTrack        echo sprintf   t  d -  -20s   s   s n             albumTrack- gt getPosition             albumTrack- gt getTitle             albumTrack- gt getDuration  - gt format  H i s             albumTrack- gt isPromoted       - PROMOTED                   You will need to examine this throughly to ensure you don t suffer performance-wise    Your current set-up is simple  efficient  and easy to understand even if some of the semantics don t quite sit right with you

User · Answer

From  album- getTrackList   you will alwas get  AlbumTrackReference  entities back  so what about adding methods from the Track and proxy   class AlbumTrackReference       public function getTitle                 return  this- gt getTrack  - gt getTitle               public function getDuration                 return  this- gt getTrack  - gt getDuration              This way your loop simplifies considerably  aswell as all other code related to looping the tracks of an album  since all methods are just proxied inside AlbumTrakcReference   foreach   album- gt getTracklist   as  track        echo sprintf   t  d -  -20s   s   s n             track- gt getPosition             track- gt getTitle             track- gt getDuration  - gt format  H i s             track- gt isPromoted       - PROMOTED                   Btw You should rename the AlbumTrackReference  for example  AlbumTrack    It is clearly not only a reference  but contains additional logic  Since there are probably also Tracks that are not connected to an album but just available through a promo-cd or something this allows for a cleaner separation also

User · Answer

You ask for the  best way  but there is no best way  There are many ways and you already discovered some of them  How you want to manage and or encapsulate association management when using association classes is entirely up to you and your concrete domain  noone can show you a  best way  I m afraid   Apart from that  the question could be simplified a lot by removing Doctrine and relational databases from the equation  The essence of your question boils down to a question about how to deal with association classes in plain OOP

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This really useful example  It lacks in the documentation doctrine 2   Very thank you   For the proxies functions can be done    class AlbumTrack extends AlbumTrackAbstract          proxy method     function getTitle          class TrackAlbum extends AlbumTrackAbstract          proxy method     function getTitle         class AlbumTrackAbstract      private  id              and        OneToMany targetEntity  TrackAlbum   mappedBy  album      protected  tracklist        OneToMany targetEntity  AlbumTrack   mappedBy  track      protected  albumsFeaturingThisTrack

User · Answer

Unidirectional  Just add the inversedBy  Foreign Column Name  to make it Bidirectional     config yaml ProductStore dcm yml ProductStore    type  entity   id      product        associationKey  true     store        associationKey  true   fields      status        type  integer 1      createdAt        type  datetime     updatedAt        type  datetime   manyToOne      product        targetEntity  Product       joinColumn          name  product id         referencedColumnName  id     store        targetEntity  Store       joinColumn          name  store id         referencedColumnName  id   I hope it helps  See you

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I think I would go with  beberlei s suggestion of using proxy methods  What you can do to make this process simpler is to define two interfaces   interface AlbumInterface       public function getAlbumTitle        public function getTracklist       interface TrackInterface       public function getTrackTitle        public function getTrackDuration        Then  both your Album and your Track can implement them  while the AlbumTrackReference can still implement both  as following   class Album implements AlbumInterface          implementation    class Track implements TrackInterface          implementation         Entity whatever    class AlbumTrackReference implements AlbumInterface  TrackInterface       public function getTrackTitle                 return  this- gt track- gt getTrackTitle               public function getTrackDuration                 return  this- gt track- gt getTrackDuration               public function getAlbumTitle                 return  this- gt album- gt getAlbumTitle               public function getTrackList                 return  this- gt album- gt getTrackList              This way  by removing your logic that is directly referencing a Track or an Album  and just replacing it so that it uses a TrackInterface or AlbumInterface  you get to use your AlbumTrackReference in any possible case  What you will need is to differentiate the methods between the interfaces a bit   This won t differentiate the DQL nor the Repository logic  but your services will just ignore the fact that you re passing an Album or an AlbumTrackReference  or a Track or an AlbumTrackReference because you ve hidden everything behind an interface     Hope this helps

User · Answer

What you are referring to is metadata  data about data  I had this same issue for the project I am currently working on and had to spend some time trying to figure it out  It s too much information to post here  but below are two links you may find useful  They do reference the Symfony framework  but are based on the Doctrine ORM   http   melikedev com 2010 04 06 symfony-saving-metadata-during-form-save-sort-ids   http   melikedev com 2009 12 09 symfony-w-doctrine-saving-many-to-many-mm-relationships   Good luck  and nice Metallica references

[php] Doctrine2: Best way to handle many-to-many with extra columns in reference table

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