Loopback: Through relations not automatically deleted

[tomcooksey]

I am quite new to loopback, so it maybe that I am missing the point, however I have defined a couple of models; MenuCategory and Image, and these have a many to many relationship. So I have defined a hasManyThrough relationship using the following configs:

MenuCategory model

{
  "name": "MenuCategory",
  "base": "PersistedModel",
  "idInjection": true,
  "options": {
    "validateUpsert": true
  },
  "mixins": {
    "I18n": {
      "i18nModel": "MenuCategoryI18N"
    }
  },
  "properties": {
    "type": {
      "type": "string",
      "required": true
    },
    "parentId": {
      "type": "number",
      "required": true
    },
    "order": {
      "type": "number"
    }
  },
  "validations": [],
  "relations": {
    "translations": {
      "type": "hasMany",
      "model": "MenuCategoryI18N",
      "foreignKey": "category_id"
    },
    "images": {
      "type": "hasMany",
      "model": "Image",
      "foreignKey": "category_id",
      "through": "CategoriesToImages"
    }
  },
  "acls": [],
  "methods": {}
}

Image model

{
  "name": "Image",
  "base": "PersistedModel",
  "idInjection": true,
  "options": {
    "validateUpsert": true
  },
  "properties": {
    "file_name": {
      "type": "string"
    },
    "url": {
      "type": "string",
      "required": true
    },
    "folder_id": {
      "type": "number",
      "required": true
    }
  },
  "validations": [],
  "relations": {
      "categories": {
          "type": "hasMany",
          "model": "MenuCategory",
          "foreignKey": "image_id",
          "through": "CategoriesToImages"
      }
  },
  "acls": [],
  "methods": {}
}

CategoriesToImages link-model:

{
  "name": "CategoriesToImages",
  "base": "PersistedModel",
  "idInjection": true,
  "options": {
    "validateUpsert": true
  },
  "properties": {
    "category_id": {
      "type": "number",
      "required": true
    },
    "image_id": {
      "type": "number",
      "required": true
    }
  },
  "validations": [],
  "relations": {
      "menucategories": {
          "type": "belongsTo",
          "model": "MenuCagegories",
          "foreignKey": "category_id"
      },
      "image": {
          "type": "belongsTo",
          "model": "Image",
          "foreignKey": "image_id"
      }
  },
  "acls": [],
  "methods": {}
}

I was under the impression that I should be able to remove a category and it rip down the entries in the link table 'categories-to-images' automatically, but this doesn't appear to be happening. I also don't appear to be able to link an image to a category using:

MenuCategory.images.add(Image);

..as the docs suggest, I just get an error.

Any help would be most grateful!

[richardpringle]

"relations": {
      "menucategories": {
          "type": "belongsTo",
          "model": "MenuCagegories", // spelled wrong
          "foreignKey": "category_id"
      },
      "image": {
          "type": "belongsTo",
          "model": "Image",
          "foreignKey": "image_id"
      }
  },

Try fixing the typo first and see what happens.

In the future (not everyone does this but they should), to get help as fast as possible, fork a loopback-sandbox and recreate the issue and put the _steps to reproduce_ in the README.md. That way I can see exactly what your setup looks like including your configs. Hope that helps!

[tomcooksey]

Hi, sorry I have been on holiday.

Thanks for the typo spot, unfortunately it didn't make a difference. I have had to write a cascade mixin. I will try and create a sandbox for the issue.

[richardpringle]

@tomcooksey,if you do manage to get a sandbox up, please post the link in here and mention me in the comment.

[eggerdo]

:+1: I can confirm this, deleting an object of a model that has a hasManyThrough relation to another model does not delete the entries in the link (through) table.

[tomcooksey]

I never managed to get a sandbox setup, but it doesn't seem like it's a difficult bug to replicate. If anyone's interested, I wrote this cascade mixin to achieve this functionality. I supply it on the basis that it worked for me and people are free to use it if it helps them:

var _ = require('lodash'),
    loopback = require('loopback');

/**
 * Mixin that does a cascade delete on related items that are identifed in the
 * settings for this mixin within a particular model
 * @param Model
 * @param options
 */
module.exports = function(Model, options) {

    Model.observe('after delete', function(ctx, next) {

        //Get the ID of the record that's being deleted
        var promises = [],
            requestContext = loopback.getCurrentContext(),
            id = requestContext.active.http.req.params.id,
            keys = Object.keys(options);

        _.each(keys, function(model) {

            var foreignKey = options[model],
                linkModel = loopback.getModelByType(model),
                where = {};

            where[foreignKey] = id;

            promises.push(linkModel.destroyAll(where));
        });

        Promise.all(promises)
            .then(function() {
                next();
            });

    });

};

Configured in model thusly:

"mixins": {
    "Cascade": {
          "linkedModelName": "foreignKey"
    },
}

[eggerdo]

:+1: thanks, the mixin seems to work fine for me too, except that I had to change

id = requestContext.active.http.req.params.id,

to

id = ctx.where.id,

[tomcooksey]

Ah yes, that was me playing with something. Glad it works!

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