The data format is as follows:
/* subset */
{
"_id" : ObjectId("5c1f795fbb0eb4399f554e08"),
"pid": objectid ("5c10cf1acd6ff5730f265a8a")//parent _id
"knowledge": "sub-knowledge"
},
/* Parent */
{
"_id" : ObjectId("5c10cf1acd6ff5730f265a8a"),
"knowledge": "parent knowledge"
},
I want to query all the parents first and return onehasChild
Field, if there is a subsetpidWith parent set_idEqual, returnstrue, otherwise returnfalse
As above, the results returned by querying the parent set should be as follows:
{
"_id" : ObjectId("5c10cf1acd6ff5730f265a8a"),
"know": "Parent Knowledge Point",
"hasChild": true
}
Hope to useAggregation
The way to solve, rather than cycle, ask great god advice!
You can refer to$lookup (aggregation)
I hope it will help you.