数组内字段使用$lookup的MongoDB聚合

// orders 集合示例
{ "_id": 1, "customerId": 101, "amount": 100 }
{ "_id": 2, "customerId": 102, "amount": 200 }

// customers 集合示例
{ "_id": 101, "name": "Alice", "email": "alice@example.com" }
{ "_id": 102, "name": "Bob", "email": "bob@example.com" }

db.orders.aggregate([
  {
    $lookup: {
      from: "customers",
      localField: "customerId",
      foreignField: "_id",
      as: "customerInfo"
    }
  }
])

// 确保 customerId 是 Number 类型，_id 是 ObjectId 类型
db.orders.aggregate([
  {
    $lookup: {
      from: "customers",
      localField: "customerId",
      foreignField: "_id",
      as: "customerInfo"
    }
  }
])

db.orders.aggregate([
  { $match: { amount: { $gt: 100 } } },
  {
    $lookup: {
      from: "customers",
      localField: "customerId",
      foreignField: "_id",
      as: "customerInfo"
    }
  }
])