MongoDB : create a view which is the union of several collections

Question

我目前有一个集合，需要拆分成几个较小的集合。有没有办法制作一个包含我所有较小集合的联合的 View ？

根据 MongoDB Manual ，我可以在管道中使用 $lookup 运算符，但它最终更像是一个“连接”而不是一个“联合”。

这是我想做的一个例子:

当前收藏:

{ _id: 1, name: "abc", country: "us" }
{ _id: 2, name: "def", country: "us" }
{ _id: 3, name: "123", country: "de" }
{ _id: 4, name: "456", country: "de" }

拆分成:

Collection_US

{ _id: 1, name: "abc", country: "us" }
{ _id: 2, name: "def", country: "us" }

Collection_DE

{ _id: 3, name: "123", country: "de" }
{ _id: 4, name: "456", country: "de" }

然后，做一个 View :

查看

{ _id: 1, name: "abc", country: "us" }
{ _id: 2, name: "def", country: "us" }
{ _id: 3, name: "123", country: "de" }
{ _id: 4, name: "456", country: "de" }

这有可能吗？

Answer 1

这与 taminov 的代码相同。

db.createView('union_view', 'us', [
  {
    $facet: {
      us: [
        {$match: {}}
      ],
      de: [
        {$limit: 1},
        {
          $lookup: {
            from: 'de',
            localField: '__unexistingfield',
            foreignField: '__unexistingfield',
            as: '__col2'
          }
        },
        {$unwind: '$__col2'},
        {$replaceRoot: {newRoot: '$__col2'}}
      ]
    },
  },
  {$project: {data: {$concatArrays: ['$us', '$de']}}},
  {$unwind: '$data'},
  {$replaceRoot: {newRoot: '$data'}}
])