如何在MongoDB $projection中使用$map

db.collection.aggregate([
  {
    $project: {
      newArrayField: {
        $map: {
          input: "$arrayField",
          as: "item",
          in: {
            // 在这里定义映射操作
          }
        }
      }
    }
  }
])

db.collection.aggregate([
  {
    $project: {
      newArrayField: {
        $map: {
          input: "$arrayField",
          as: "item",
          in: {
            newField: { $addFields: ["$$item.field1", "$$item.field2"] },
            doubledField: { $multiply: ["$$item.field3", 2] },
            concatenatedField: { $concat: ["$$item.field4", "suffix"] }
          }
        }
      }
    }
  }
])