Тъй като се опитвате да използвате $lookup
функции (синтаксис) от MongoDB v3.6 на MongoDB v3.4
MongoDB v3.4 $lookup
синтаксис:
{
$lookup:
{
from: <collection to join>,
localField: <field from the input documents>,
foreignField: <field from the documents of the "from" collection>,
as: <output array field>
}
}
MongoDB v3.6 $lookup
синтаксис:
{
$lookup:
{
from: <collection to join>,
let: { <var_1>: <expression>, …, <var_n>: <expression> },
pipeline: [ <pipeline to execute on the collection to join> ],
as: <output array field>
}
}
https://docs.mongodb.com/manual/reference/operator/ агрегиране/търсене/