Sequelize: Changing the nested data structure

I want to change the data structure returned by the orm query. There are four tables in total. product,category are many-to-many relationships, there is a product_category table that serves as a bridge, and a total of four tables, including thedepartment table. association is as follows:

// product
product.belongsToMany(models.category, {
      through: 'product_category',
      foreignKey: 'product_id'
});

// product_category
product_category.belongsTo(models.product, {
      foreignKey: 'product_id'
});
product_category.belongsTo(models.category, {
      foreignKey: 'category_id'
});

// category
category.belongsToMany(models.product, {
      through: 'product_category',
      foreignKey: 'category_id'
});
category.belongsTo(models.department, {
      foreignKey: 'department_id'
});

// department
department.hasMany(models.category, {
      foreignKey: 'department_id'
});

Through the above table structure, the following query is obtained to obtain products corresponding to department_id:

const query = await product.findOne({
   where: { product_id: id },
   include: {
     model: category,
     attributes: ['category_id', ['name', 'category_name']],
     include: {
       model: department,
       attributes: ['department_id', ['name', 'department_name']]
     }
   },
   attributes: []
});

const data = query.categories;

The resulting json data is as follows:

"data": [
    {
        "category_id": 1,
        "category_name": "French",
        "department": {
            "department_id": 1,
            "department_name": "Regional"
        },
        "product_category": {
            "product_id": 1,
            "category_id": 1
        }
    }
]

I want to make the above data as follows:

"data": [
    {
         "category_id": 1,
         "category_name": "French",
         "department_id": 1,
         "department_name": "Regional"
    }
]

In order to process the data as above, there are two ways to modify the sql-based orm query and to process the product value in javascript. However, since I learned sql with orm, I did not know the first method, so I decided to use it as the second method.

The first attempt

I made two attempts. Note that the framework uses koa.js. The first is as follows:

const query = await product.findOne({
  where: { product_id: id },
  include: {
    model: category,
    attributes: ['category_id', ['name', 'category_name']],
    include: {
      model: department,
      attributes: ['department_id', ['name', 'department_name']]
    }
  },
  attributes: []
});

const data = query.categories.map(
      ({ category_id, category_name, department }) => ({
        category_id,
        category_name,
        department_id: department.department_id,
        department_name: department.department_name
      })
    );

ctx.body = data;

Below is the body:

"data": [
    {
        "category_id": 1,
        "department_id": 1
    }
]

..?? Something is strange, so I change the return value slightly:

({ category_id, category_name, department }) => ({
        // category_id,
        // category_name,
        department_id: department.department_id,
        department_name: department.department_name
      })

The json value output is:

"data": [
    {
        "department_id": 1
    }
]

Conversely, you annotated department_id,department_name:

({ category_id, category_name, department }) => ({
        category_id,
        category_name,
        // department_id: department.department_id,
        // department_name: department.department_name
      })

The resulting json value is:

"data": [
    {
        "category_id": 1
    }
]

I could not do it any other way.

The second attempt

await product
.findOne({
  where: { product_id: id },
  include: {
    model: category,
    attributes: ['category_id', ['name', 'category_name']],
    include: {
      model: department,
      attributes: ['department_id', ['name', 'department_name']]
    }
  },
  attributes: []
})
.then(query => {
  const data = query.categories.map(
    ({ category_id, category_name, department }) => ({
      category_id,
      category_name,
      department_id: department.department_id,
      department_name: department.department_name
    })
  );

  ctx.body = data;
});

Both methods have the same results, so I do not know what to do.

So i map the variable to the nested array with json data. I get the result I want:

const data = {
  categories: [
    {
      category_id: 1,
      category_name: 'French',
      department: { department_id: 1, department_name: 'Regional' },
      product_category: { product_id: 1, category_id: 1 }
    }
  ]
};

const product = data.categories.map(
  ({ category_id, category_name, department }) => ({
    category_id,
    category_name,
    department_id: department.department_id,
    department_name: department.department_name
  })
);

console.log(product);

// [ { category_id: 1,
//    category_name: 'French',
//    department_id: 1,
//    department_name: 'Regional' } ]

So I got confused. How can I process data from a sequelize query? I would really appreciate your help.

Please let me know if the approach to solving the problem is wrong or you need a model schema.