Mongodb 与 future 文档的聚合

Question

我正在寻找有关如何在 MongoDB 中最好地处理此类查询的一些指导。

我有一个购买数据库，每个数据库都有一个类(class)属性以及购买者的购买日期。

我想要的是某人购买初始产品后发生的购买列表。

所以 - 这里有一些伪查询:

// first find everyone who signed up for course A
{ course: 'a' }

然后

/*
  out of those people, filter for those who in the future signed up
  for another course
*/

{
  course: { $in: ['b','c','d']},
  date: { $gt: $courseA.purchaseDate }
}

聚合是否可能？或者我会为每次初始购买进行多次数据库调用以检查是否有 future ？

以下是每次购买的数据示例:

{ email: 'wes@example.com', course: 'a', purchaseDate: 10 },
{ email: 'wes@example.com', course: 'b', purchaseDate: 20 }, // match
{ email: 'wes@example.com', course: 'c', purchaseDate: 5 }, // not
{ email: 'nancy@example.com', course: 'a', purchaseDate: 5 },
{ email: 'nancy@example.com', course: 'c', purchaseDate: 6 }, // match
{ email: 'nancy@example.com', course: 'b', purchaseDate: 10 }, // match
{ email: 'nancy@example.com', course: 'd', purchaseDate: 1 }, // not

Answer 1

在 Twitter 上的一些帮助下找到了答案

.aggregate([
  // Project the target purchasedate
  { $match: { course: { $in: ['JS3', 'RDX', 'WTF', 'RFB', 'ES6']}}},
  { $project: {
    email: 1, amount: 1, course: 1, purchaseDate: 1,
    target: {
      $cond: {
        if: { $eq: ['$course', 'JS3'] },
        then: "$purchaseDate",
        else: 0,
      }
    }
  }},
  // Group records by email, storing the target and the highest encountered purchase date
  { $group: {
    _id: '$email',
    courses: { $push: '$course'},
    amounts: { $push: '$amount'},
    count: { $sum: 1 },
    spent: { $sum: '$amount' },
    target: { $first: '$target'},
    max: { $max: '$purchaseDate'}
  }},
  // // Check if the highest encountered date is greater then the target
  { $project: {
    email: 1, course: 1, amounts: 1, spent: 1, count: 1, courses: 1, target:1, max: 1,
    selected: { $cond: [{ $gt: ['$max', '$target']}, true, false] }
  }},
  // Filter out the non-matches
  { $match: {
    target: { $gt: 0 },
    selected: true,
    spent: { $gt: 0 },
  }},
  { $sort: { spent: -1 }}
])