Relationship between same entity

[Aristeidis Bampakos]

Hello,

Is it possible to have relationship between records of the same entity? For example:

var Attraction = persistence.define('attraction', {

          name: "TEXT",

          description: "TEXT"

});

Attraction.hasMany('relAttractions', Attraction, 'attraction')

That is, an attraction can have many attractions as relAttractions.

Thanks,

[Zef Hemel]

I think that should work, yes as long as you have different property names for each end (as you do).

-- Zef

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[Aristeidis Bampakos]

Hello Zef,

Thank you very much for your response.

I have created a method that adds an attraction with its related ones and seems to be working fine, since I can see data correctly through my app. When I refresh the page, I get the following error in the call of persistence.loadFromLocalStorage() :

Error: Property 'attraction' of 'attraction' with id: '9D2A124C-6CAE-4AC6-8815-F21E3060E553' not fetched, either prefetch it or fetch it manually.

If I use a separate entity for related attractions, the error does not show up.

[Zef Hemel]

How are you loading the data on page load?

-- Zef

[Aristeidis Bampakos]

 persistence.loadFromLocalStorage();
              
              // find the attraction by ID
              Attraction.load(id, function(a){
                  if(a != null){
                    callback(a);
                  }
              });

[Zef Hemel]

Alright, the problem may be that you have to fetch the "attraction" property explicitly before you access it using the "fetch" method:

Attraction.load(id, function(a){
  if(a != null

){
       a.fetch("attraction", function() {
          callback(a);
       });
  }
});

When you use Attract.list() queries, you can do this by using .prefetch("attraction") (which will generate a JOIN for you), also see the documentation on "prefetch" and "fetch" in the README.md

-- Zef

[Aristeidis Bampakos]

OK, but why is the error caught in the first line of the code:

persistence.loadFromLocalStorage();

and not afterwards?

[Zef Hemel]

It's only thrown if the object in question (the one that the .attraction attribute points to) is not already loaded in memory. In the other context probably you had the object in memory already so it works, but on a fresh page load that won't be the case.

-- Zef

[Aristeidis Bampakos]

When persistence.loadFromLocalStorage() is called, does't load the database in memory? Should I call some other function to do the trick?

[Aristeidis Bampakos]

I made some debugging in persistence.store.memory.js and found that the error is thrown in method persistence.set (line 93) of persistence.js when tries to set attraction property. 

Perhaps, it falls in some sort of cyclical reference because the attraction property of the current Attraction has its own attraction property which has another attraction property etc....