# Smart hasMany relationship in mongoDB

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## Smart hasMany relationship in mongoDB

**Context**: As a user I want to display records that have a belongsTo relationship to another record as related data of this record.

Parent collection: `user`

Child collection: `visualization`

### Models definition

`models/user.js`

```jsx
// This model was generated by Lumber. However, you remain in control of your models.
// Learn how here: <https://docs.forestadmin.com/documentation/v/v6/reference-guide/models/enrich-your-models>
const mongoose = require('mongoose');

// This section contains the properties of your model, mapped to your collection's properties.
// Learn more here: <https://docs.forestadmin.com/documentation/v/v6/reference-guide/models/enrich-your-models#declaring-a-new-field-in-a-model>
const schema = mongoose.Schema(
  {
    avatar_link: String,
    client: { type: mongoose.Schema.Types.ObjectId, ref: 'client' },
    date_added: Date,
    email: String,
    first_name: String,
    last_name: String,
    user_type: String,
  },
  {
    timestamps: false,
  }
);

module.exports = mongoose.model('user', schema, 'user');
```

`models/visualization.js`

```jsx
// This model was generated by Lumber. However, you remain in control of your models.
// Learn how here: <https://docs.forestadmin.com/documentation/v/v6/reference-guide/models/enrich-your-models>
const mongoose = require('mongoose');

// This section contains the properties of your model, mapped to your collection's properties.
// Learn more here: <https://docs.forestadmin.com/documentation/v/v6/reference-guide/models/enrich-your-models#declaring-a-new-field-in-a-model>
const schema = mongoose.Schema(
  {
    description: String,
    name: String,
    user: { type: mongoose.Schema.Types.ObjectId, ref: 'user' },
    visualization_type: String,
  },
  {
    timestamps: false,
  }
);

module.exports = mongoose.model('visualization', schema, 'visualization');
```

### Declaration of the relationship

As the relationship that is not present in your database structure, declare it at the level of the forest folder.

`forest/user.js`

```jsx
const { collection } = require('forest-express-mongoose');
const { customFieldsStyles } = require('../style/fields-style.js');

// This file allows you to add to your Forest UI:
// - Smart actions: <https://docs.forestadmin.com/documentation/reference-guide/actions/create-and-manage-smart-actions>
// - Smart fields: <https://docs.forestadmin.com/documentation/reference-guide/fields/create-and-manage-smart-fields>
// - Smart relationships: <https://docs.forestadmin.com/documentation/reference-guide/relationships/create-a-smart-relationship>
// - Smart segments: <https://docs.forestadmin.com/documentation/reference-guide/segments/smart-segments>
collection('user', {
  actions: [],
  fields: [
    {
      field: 'visualizations',
      type: ['String'],
      reference: 'visualization._id',
    },
  ],
  segments: [],
});
```

### Implementation of the get route for the relationship

The route to get the related visualizations when you are on a user page needs to be implemented in the routes folder.

`routes/user.js`

```javascript
const express = require('express');
const { PermissionMiddlewareCreator, RecordSerializer } = require('forest-express-mongoose');
const mongoose = require('mongoose');
const { visualization } = require('../models');

const router = express.Router();
const permissionMiddlewareCreator = new PermissionMiddlewareCreator('user');

...

router.get('/user/:recordId/relationships/visualizations', permissionMiddlewareCreator.details(), async (req, res, next) => {
  const limit = parseInt(req.query.page.size) || 10;
  const offset = (parseInt(req.query.page.number) - 1) * limit;
  const userObjectId = mongoose.Types.ObjectId(req.params.recordId);
  const visualizationSerializer = new RecordSerializer({ modelName: 'visualization' });
  const count = await visualization.countDocuments({ user: userObjectId });
  const data = await visualization.find({ user: userObjectId }, null, { skip: offset, limit });
  const dataSerialized = await visualizationSerializer.serialize(data, { count });
  res.send(dataSerialized);
});

module.exports = router;j
```