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🦸 Advanced Aggregation Pipelines

You can also use aggregation pipelines to perform more advanced operations on your data.

Exercises​

Try finding the answer to the following questions using aggregation pipelines.

Return a collection with the cast members of the movie with the most comments.​

Answer
[
  {
    $sort:
      /**
       * Provide any number of field/order pairs.
       */
      {
        num_mflix_comments: -1,
      },
  },
  {
    $limit:
      /**
       * Provide the number of documents to limit.
       */
      1,
  },
  {
    $unwind:
      /**
       * path: Path to the array field.
       * includeArrayIndex: Optional name for index.
       * preserveNullAndEmptyArrays: Optional
       *   toggle to unwind null and empty values.
       */
      {
        path: "$cast",
      },
  },
  {
    $project:
      /**
       * Specifications: The fields to
       *   include or exclude.
       */
      {
        cast: 1,
      },
  },
]

What are the three countries that produced the most Dramas?​

Answer
[
  {
    $match:
      /**
       * query: The query in MQL.
       */
      {
        genres: "Drama",
      },
  },
  {
    $unwind:
      /**
       * path: Path to the array field.
       * includeArrayIndex: Optional name for index.
       * preserveNullAndEmptyArrays: Optional
       *   toggle to unwind null and empty values.
       */
      {
        path: "$countries",
      },
  },
  {
    $group:
      /**
       * _id: The id of the group.
       * fieldN: The first field name.
       */
      {
        _id: "$countries",
        count: {
          $sum: 1,
        },
      },
  },
  {
    $sort:
      /**
       * Provide any number of field/order pairs.
       */
      {
        count: -1,
      },
  },
  {
    $limit:
      /**
       * Provide the number of documents to limit.
       */
      3,
  },
]

Which actor appears in the highest number of movies?​

Answer
[
  {
    $unwind:
      /**
       * path: Path to the array field.
       * includeArrayIndex: Optional name for index.
       * preserveNullAndEmptyArrays: Optional
       *   toggle to unwind null and empty values.
       */
      {
        path: "$cast",
      },
  },
  {
    $group:
      /**
       * _id: The id of the group.
       * fieldN: The first field name.
       */
      {
        _id: "$cast",
        count: {
          $sum: 1,
        },
      },
  },
  {
    $sort:
      /**
       * Provide any number of field/order pairs.
       */
      {
        count: -1,
      },
  },
  {
    $limit:
      /**
       * Provide the number of documents to limit.
       */
      1,
  },
]