Tips on transforming a list of objects containing arrays of elements into an array of objects with those sub-elements as properties

Question

Tips on transforming a list of objects containing arrays of elements into an array of objects with those sub-elements as properties

Background

Working on a Node.js project utilizing Mongoose and Pug as the templating engine

Sample JSON data retrieved via Mongoose

[
    {
        "name": "user1",
        "blogs": [
            {
                "title": "blog1",
                "created": "01-01-2020"
            },
            {
                "title": "blog2",
                "created": "01-01-2020"
            }
        ]
    },
    {
        "name": "user2",
        "blogs": [
            {
                "title": "blog3",
                "created": "01-01-2020"
            },
            {
                "title": "blog4",
                "created": "01-01-2020"
            }
        ]
    }
]

Issue

The goal is to display a list of blog posts sorted by creation date while showing the respective user who created each post.

When trying to render the object in Pug using a foreach loop, the data gets grouped by user making it difficult to sort based on creation dates across all blog entries.

Solution involves restructuring the object as follows:

Transformed JSON data mapping each blog post to its user

[
    {
        "name": "user1",
        "blog": {
            "title": "blog1",
            "created": "01-01-2020"
        }
    },
    {
        "name": "user1",
        "blog": {
            "title": "blog2",
            "created": "01-01-2020"
        }
    },
    {
        "name": "user2",
        "blog": {
            "title": "blog3",
            "created": "01-01-2020"
        }
    },
    {
        "name": "user2",
        "blog": {
            "title": "blog4",
            "created": "01-01-2020"
        }
    }
]

This revised data structure allows for displaying user details alongside each blog post and enables sorting by performance creation date.

The challenge lies in achieving this without excessive looping or mapping techniques.

Note

To address this issue, establishing a relationship and resolving keys would be straightforward. The focus here, however, is exploring solutions within a NoSQL context.

How would you approach this scenario and what term best describes this specific operation?

javascript arrays mongodb mongoose lodash

Answer 1

Answer №1

Instead of pulling data from the database in a undesired format and then converting it to the desired format, you can utilize aggregation to directly retrieve the data from MongoDB in the preferred format:

db.collection.aggregate([
  { $unwind: "$blogs" },
  {
    $project: {
      "_id": 0,
      name: 1,
      blogs: 1,
      date: {
        $dateFromString: {
          dateString: "$blogs.created"
        }
      }
    }
  },
  { $sort: { date: -1 } },
  { $project: { date: 0 } }
])

Explanation of the stages used in the above query:

$unwind - Breaks down the blogs array into individual documents with each object in the array
$project - Omits the _id field, reveals the name and blogs fields, creates a new field called date with the value converted from the created field to a date.
$sort - Arranges the documents based on the date field in descending order (from most recent to oldest date)
$project - Conceals the date field in the output documents

For more information on the mentioned aggregation stages, refer to:

Demo:

View this demo to see the query in action.

Answer 2

Instead of pulling data from the database in a undesired format and then converting it to the desired format, you can utilize aggregation to directly retrieve the data from MongoDB in the preferred format:

db.collection.aggregate([
  { $unwind: "$blogs" },
  {
    $project: {
      "_id": 0,
      name: 1,
      blogs: 1,
      date: {
        $dateFromString: {
          dateString: "$blogs.created"
        }
      }
    }
  },
  { $sort: { date: -1 } },
  { $project: { date: 0 } }
])

Explanation of the stages used in the above query:

$unwind - Breaks down the blogs array into individual documents with each object in the array
$project - Omits the _id field, reveals the name and blogs fields, creates a new field called date with the value converted from the created field to a date.
$sort - Arranges the documents based on the date field in descending order (from most recent to oldest date)
$project - Conceals the date field in the output documents

For more information on the mentioned aggregation stages, refer to:

Demo:

View this demo to see the query in action.

Answer 3

Answer №2

One approach is to use Array.prototype.reduce. Here's an example that demonstrates this:

const data = [
    {
        "name": "user1",
        "blogs": [
            {
                "title": "blog1",
                "created": "01-01-2020"
            },
            {
                "title": "blog2",
                "created": "01-01-2020"
            }
        ]
    },
    {
        "name": "user2",
        "blogs": [
            {
                "title": "blog3",
                "created": "01-01-2020"
            },
            {
                "title": "blog4",
                "created": "01-01-2020"
            }
        ]
    }
];

const result = data.reduce((acc, curr) => {
    const { name, blogs } = curr;
    const blogArr = blogs.map((blog) => {
        return {
            name,
            blog
        };
    });

    Array.prototype.push.apply(acc, blogArr);
    return acc;
}, []);

console.log(result);

Answer 4

One approach is to use Array.prototype.reduce. Here's an example that demonstrates this:

const data = [
    {
        "name": "user1",
        "blogs": [
            {
                "title": "blog1",
                "created": "01-01-2020"
            },
            {
                "title": "blog2",
                "created": "01-01-2020"
            }
        ]
    },
    {
        "name": "user2",
        "blogs": [
            {
                "title": "blog3",
                "created": "01-01-2020"
            },
            {
                "title": "blog4",
                "created": "01-01-2020"
            }
        ]
    }
];

const result = data.reduce((acc, curr) => {
    const { name, blogs } = curr;
    const blogArr = blogs.map((blog) => {
        return {
            name,
            blog
        };
    });

    Array.prototype.push.apply(acc, blogArr);
    return acc;
}, []);

console.log(result);

Answer 5

Answer №3

One effective method I would employ is utilizing MongoDB's aggregation feature. The beauty of aggregation lies in its ability to allow you to format your data as desired before retrieving it.

The process of aggregation operates in a sequential manner, with a series of commands executed in the specified order.

In this scenario, the aggregation pipeline would take on the following structure:

[{
    $unwind: {
        path: '$blogs'
    }
}, {
    $project: {
        _id: 0,
        name: 1,
        blog: '$blogs'
    }
}, {
    $sort: {
        "blogs.created": -1
    }
}]

The commands utilized within this pipeline include:

$unwind - This command disassembles an array of items into separate documents, each maintaining the original fields except for the unwound field containing all deconstructed objects.

$project - It offers flexibility in data formatting by allowing field removal, addition, and renaming.

$sort - As implied, this command facilitates document sorting based on specified fields and ordering (ascending or descending).

To delve deeper into aggregation, refer to MongoDB's official documentation:

Answer 6

One effective method I would employ is utilizing MongoDB's aggregation feature. The beauty of aggregation lies in its ability to allow you to format your data as desired before retrieving it.

The process of aggregation operates in a sequential manner, with a series of commands executed in the specified order.

In this scenario, the aggregation pipeline would take on the following structure:

[{
    $unwind: {
        path: '$blogs'
    }
}, {
    $project: {
        _id: 0,
        name: 1,
        blog: '$blogs'
    }
}, {
    $sort: {
        "blogs.created": -1
    }
}]

The commands utilized within this pipeline include:

$unwind - This command disassembles an array of items into separate documents, each maintaining the original fields except for the unwound field containing all deconstructed objects.

$project - It offers flexibility in data formatting by allowing field removal, addition, and renaming.

$sort - As implied, this command facilitates document sorting based on specified fields and ordering (ascending or descending).

To delve deeper into aggregation, refer to MongoDB's official documentation:

Tips on transforming a list of objects containing arrays of elements into an array of objects with those sub-elements as properties

Background

Issue

Transformed JSON data mapping each blog post to its user

Note

Answer №1

Demo:

Answer №2

Answer №3

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