Is it possible to set a $hint in a pipeline in a lookup?
{
"$lookup": {
"from": "events",
"let": {
"cId": "$_id"
},
"pipeline": [
{
"$match": {
"$expr": {
"$and": [
{
"$eq": [
"$contact_id",
"$$cId"
]
}]}
}},
{
"$group": {
"_id": "$contact_id",
"609148080548ab43fb3c9c83": {
"$sum": {
"$cond": [
{
"$and": [
{
"$eq": [
"$channel",
"form"
]
},
{
"$eq": [
"$event",
"submitted"
]
},
{
"$eq": [
"$form_id",
ObjectId( "6000194aae91a5ea3fa9975b" )
]
}
]
},
1,
0
]
}
}
}
}
],
"as": "events"
}
}
In the lookup above I would like to have a hint like this
“$hint”, { contact_id: 1, channel: 1, form_id: 1, event: 1 }
What is the correct syntax?