How to retrieve records for a many to many relationship? about feathers-sequelize

[daffl]

I am not too familiar with the more complex side of Sequelize but looking at the Relations/Associations docs, once you associated an m:n relationship you could just register a service that gets the related entities:

app.use('/api/v1/intents/:intentId/entities', {
  find(params) {
    const id = params.intentId;
    return app.service('intents').get(id)
      .then(intent => intent.getEntities());
  },

  setup(app) {
    this.app = app;
  }
});

[ekryski]

@lionelrudaz or you can just do that same call to the intents service in a before hook of a entities service. We have found that you rarely need to nest routes like that and instead should have them flatter and use something like an intentId. See http://docs.feathersjs.com/middleware/routing.html#nested-routes.

So you'd have:

function getIntents() {
  return function(hook) {
    return Prmise(function(resolve, reject) {
      hook.app.service('intents').get(hook.params.query.intentId).then(result => {
         hook.params.intent = result;
         resolve(hook);
      }).catch(reject);
    };
  };
}

app.use('intents', service());
app.use('intent_entites', service());

app.service('intent_entities').before({
  find: [
    getIntents()
  ]
})

That should more or less do it.

[ekryski]

I'm going to close this as both of those options should work. @lionelrudaz can you report back to let us know if one of those works or not? If not, we can re-open and dig deeper.

[lionelrudaz]

Thanks both of you for your answers.

I tried both options, can't make work either of them.

@daffl, theoretically, everything should work as you suggest. The thing is that I believe the relationship is somehow unknown at this step. I get the following error:

TypeError: intent.getEntities is not a function

Here's how I set the relationships up in services/index.js:

/* jshint esversion: 6 */

import language from './language';
import conversation from './conversation';
import message from './message';
import category from './category';
import intent from './intent';
import entity from './entity';
import intententity from './intent-entity';

import Sequelize from 'sequelize';

export default function() {
  const app = this;

  const sequelize = new Sequelize(app.get('postgres'), {
    dialect: 'postgres',
    logging: console.log
  });

  app.set('sequelize', sequelize);

  app.configure(language);
  app.configure(message);
  app.configure(conversation);
  app.configure(category);
  app.configure(intent);
  app.configure(entity);
  app.configure(intententity);

  let models = sequelize.models;
  models.intent.belongsToMany(models.entity, {through: 'IntentEntity'});
  models.entity.belongsToMany(models.intent, {through: 'IntentEntity'});

  sequelize.sync();
}

I imagine that on IntentEntity service, the relationship is unknown. I tried to move the relationship before configuring IntentEntity service, but that doesn't change anything.

Any ideas?

@ekryski: your solution will work as a charm with a 1:n relationship. The thing is that I don't have an intentId column in my Entities model, so that can't work like that, unless I'm missing a point. But working with flat URLs can work as well, no problem. It doesn't change the root question: how can I make a query with a join on the relationship table?

Let me know if you need anything else.

[lionelrudaz]

Hi guys,

I tried a few other workarounds, but I'm unable to make that work. Am I the only one in that situation? Haven't you been in front of many-to-many relationships? I can't find any example that helped me so far.

Thanks again for your help.

Cheers,

Lionel

[daffl]

For me not with Sequelize. Did you get some test code working with just the plain model definitions as described in the Sequelize documentation?

[ekryski]

@lionelrudaz I'll try and cook up a demo app to see if I can get this sorted. In all honesty I haven't run into many-to-many relationships all that often.

[lionelrudaz]

@daffl I can try again with a very simple application to see if it behaves correctly. From that part, I think that the association is not yet available when I work in the services. I don't know if it helps.

@ekryski Do you want a link to my app? Maybe it can help.

[ekryski]

@lionelrudaz sure that would help.

[lionelrudaz]

Here you go: https://github.com/lionelrudaz/wellnow-node

[ekryski]

@lionelrudaz took a quick look. Overall looks really good! Makes me really happy to see how someone else is using Feathers. I'll take a more detailed look a little later today just in the middle of working on authentication right now. I think we should be able to solve this pretty easily.

[lionelrudaz]

No problem.

Your new example really helps building beautiful apps from the ground up. I just modified the structure to add a models folder, because I found that cleaner.

Let me know if I can be from any help.

[lionelrudaz]

I worked a bit this evening. I believe the key is that associations aren't existing when I do this in my intent entity service:

app.use('/api/v1/intents/:intentId/entities', {
    find(params) {
      const id = params.intentId;
      return app.service('api/v1/intents').get(id)
        .then(intent => intent.getEntities());
    }
  });

It still tells me that there's no getEntities method for intent. My conclusion is that the intent service provides a model instance and that this model instance doesn't know the relationship with Entity.

I tried to move a bit the logic, by loading models from an index.js file in my models folder. In parallel, I removed the connection with the DB in the services. I changed the intent, entity and intent entity services to use the models that I instantiate from the models module.

I also added a new IntentEntity model to take care of the relationship.

I'm still at the same stage, so I don't know if you have any clue.

I uploaded my work in a new branch: https://github.com/lionelrudaz/wellnow-node/tree/many-to-many

Let me know if you need more information.

[lionelrudaz]

OK, I think I made it.

My idea: load all models with index.js in the models folder. Set the associations right there.

Then, for the particular services using a many-to-many relationship, I can do this:

app.use('/api/v1/intents/:intentId/entities', {
    find(params) {
      const id = params.intentId;
      return models.entity.findAll({
        include: [
           { model: models.intent, where: { id: id }}
        ]
      });
    },
    create(data, params) {
      const id = params.intentId;
      return models.entity.create(data).then(function(entity) {
        entity.addIntent(id);
        return entity;
      });
    }
  });

Can you briefly tell me it's not horrible and that I can proceed with the next services that have these kinds of associations?

My app is updated there: https://github.com/lionelrudaz/wellnow-node

Thanks in advance

[ekryski]

@lionelrudaz Woot! If it's working then it definitely looks good to me. 😄 Nice work.

I'm busy working on the news Feathers website so sorry I didn't really have time to play around with Many-to-many relationships.

[lionelrudaz]

No problem, totally get it. All the best for the new website. I close then

[lopezjurip]

On client side, params.intentId is undefined.

const io = require('socket.io-client');
const feathers = require('feathers/client');
const hooks = require('feathers-hooks');
const socketio = require('feathers-socketio/client');
const authentication = require('feathers-authentication/client');

const socket = io('http://localhost:3030');
const client = feathers()
  .configure(hooks())
  .configure(socketio(socket))
  .configure(authentication());

client.service('/api/v1/intents/:intentId/entities').find({ intentId: 1 })
  .then(entities => console.log(entities))
  .catch(err => console.error(err));

But with server-side feathersjs app instance, the param intentId is passed correctly.

[daffl]

Can you create a new issue for that? This is kind of a bug (because only params.query is passed between client and server) but I am not sure how to solve that yet. A workaround is to map it to params.query.intendId.

[lopezjurip]

Issue: feathersjs/feathers#304