MongoDB addfields 基于过滤条件

Question

I have data for jstree in the flat array format

{"glob":[
{
id:"1",
text:"Parent",
parent:"#"
},
{
id:"2",
text:"child1",
parent:"1"
},
{
id:"3",
text:"child2",
parent:"1"
},
{
id:"4",
text:"grandchild1",
parent:"3"
},
]}

I want to retrieve the children of a particular node id along with an attribute to explain whether the node has children.

So, if I retrieve the children for node id '1', the expected result is

[{
id:"2",
text:"child1",
parent:"1",
children: false
},
{
id:"3",
text:"child2",
parent:"1",
children: true
}]

Can you please suggest the right stages I have to use

Answer 1

Since the documents are originally nested we cant use $graphLookup or $lookup which are built for such cases. One option is to:

1. Create an array of items that are children of the wanted node (called data )
2. Create a set of nodes in data which have children (called childrenExists )
3. Unwind data as you want the answer as separate documents.
4. format the answer.

db.collection.aggregate([
  {$set: {
      data: {
        $filter: {input: "$glob", cond: {$eq: ["$$this.parent", "1"]}}
      }
    }
  },
  {$project: {
      _id: 0,
      data: 1,
      childrenExists: {
        $reduce: {
          input: "$glob",
          initialValue: [],
          in: {$setUnion: [
              "$$value",
              {$cond: [
                  {$in: ["$$this.parent", "$data.id"]},
                  ["$$this.parent"],
                  []
              ]}
          ]}
        }
      }
    }
  },
  {$unwind: "$data"},
  {$set: {
      "data.children": {
        $cond: [{$in: ["$data.id", "$childrenExists"]}, true, false]
      },
      childrenExists: "$$REMOVE"
    }
  },
  {$replaceRoot: {newRoot: "$data"}}
])

See how it works on the playground example