MongoDB嵌套数组查询与更新：获取及修改指定座位数

First, let's translate your Java aggregation logic into a MongoDB shell query that does exactly the same thing:

Aggregation Query (Matching Your Java Code) #

db.cities.aggregate([
  // Filter to get only the Bangalore city document
  { $match: { name: "Bangalore" } },
  // Unwind the movies array to work with individual movie entries
  { $unwind: "$movies" },
  // Filter to keep only the Avengers movie
  { $match: { "movies.name": "Avengers" } },
  // Unwind the theatres array for that movie
  { $unwind: "$movies.theatres" },
  // Filter to keep only the IMAX theatre
  { $match: { "movies.theatres.name": "IMAX" } },
  // Group by seats (though since we've filtered to one theatre, this just returns the seat value as _id)
  { $group: { _id: "$movies.theatres.seats" } }
])

This will return { "_id": 50 } just like your Java code does.

Alternative Aggregation Approach (More Direct) #

Instead of unwinding multiple times, you can use array operators like $filter and $arrayElemAt to directly target the specific theatre's seats without flattening the arrays:

db.cities.aggregate([
  { $match: { name: "Bangalore" } },
  { $project: {
      // First, filter the movies array to get only Avengers
      targetMovie: { $arrayElemAt: [
          { $filter: {
              input: "$movies",
              cond: { $eq: ["$$this.name", "Avengers"] }
            }
          }, 0
        ]
      },
      _id: 0
    }
  },
  { $project: {
      // Then filter the theatres array of that movie to get IMAX
      targetTheatre: { $arrayElemAt: [
          { $filter: {
              input: "$targetMovie.theatres",
              cond: { $eq: ["$$this.name", "IMAX"] }
            }
          }, 0
        ]
      }
    }
  },
  { $project: {
      // Extract just the seats value
      seats: "$targetTheatre.seats"
    }
  }
])

This returns { "seats": 50 }, which is a more straightforward result if you just need the number.

Updating the Seat Count #

To update the seats for Bangalore -> Avengers -> IMAX, use MongoDB's positional filtered operators to target the exact nested elements safely:

db.cities.updateOne(
  // Query to find the correct city document
  { name: "Bangalore" },
  // Update the seats value (replace 55 with your desired new count)
  { $set: { "movies.$[movie].theatres.$[theatre].seats": 55 } },
  // Array filters to match the specific movie and theatre
  { arrayFilters: [
      { "movie.name": "Avengers" },
      { "theatre.name": "IMAX" }
    ]
  }
)

This will only modify the seats count for the specified theatre, leaving all other entries in your arrays untouched.

内容的提问来源于stack exchange，提问作者Deepanshu Gautam