MongoDb-$lookup with where子句

考虑到这样的情况：

帖子：

post: {
 subject: 'test',
 category: 123,
 author: 1
}

{
 id: 1,
 name: 'foo'
}

{
 id: 123,
 name: 'bar'
}

用户：

post: {
 subject: 'test',
 category: 123,
 author: 1
}

{
 id: 1,
 name: 'foo'
}

{
 id: 123,
 name: 'bar'
}

类别：

post: {
 subject: 'test',
 category: 123,
 author: 1
}

{
 id: 1,
 name: 'foo'
}

{
 id: 123,
 name: 'bar'
}

如何对sql执行等效查询：

SELECT * 
FROM posts
JOIN users on posts.author = user.id
JOIN category on posts.category = category.id
WHERE users.name = 'foo' and category.name = 'bar' //this is the problem

我一直在尝试项目/查找，但我不知道如何在查找本身中添加“where”（或者这是否是查询此内容的正确方法）

db.posts.aggregate(
[
    {
        $project: { 'subject': '$subject' },
    },
    {
        $lookup: {
            from: 'users',
            localField: 'author',
            foreignField: 'id',
            as: 'test'
        }
    },    
])

---

您必须使用两个

$lookup

[
  {
    "$lookup": {
      "from": "users",
      "localField": "post.author",
      "foreignField": "id",
      "as": "userJoin"
    }
  },
  {
    "$lookup": {
      "from": "category",
      "localField": "post.category",
      "foreignField": "id",
      "as": "categoryJoin"
    }
  },
  {
    $match: {
      "categoryJoin.name": "bar",
      "userJoin.name": "foo"
    }
  }
]

---

工作

谢谢，有没有办法将查找字段作为单个项目（如findOne）而不是数组返回？您可以使用

arrayElemAt

和

ifNull