It is possible to perform multiple $lookups in a single query, on the same collection, on fields that are derived using $addFields. A suggestion was made in a case that perhaps our documentation could be updated to indicate this. For example a query like this is possible:

{$match: {id: {$in: [/^123456/ ,
/^123457/
]}}},
{"$addFields":{
"BlockKey": {$concat: [ "L", { $substr: [ "$id", 0, 7 ]}] },
"CodeKey": {$concat: [ "L", { $substr: [ "$_id", 0, 6 ]},"A"] }
}},
{ $lookup: {
from: "port_ss_col",
localField: "BlockKey",
foreignField: "_id",
as: "BlockArray"
}},
{ $lookup: {
from: "port_ss_col",
localField: "CodeKey",
foreignField: "_id",
as: "CodeArray"
}},
{ $project: {...

If that's not possible (or if this doc-addition doesn't make sense), that's fine; it's understood that every query use case cannot be included in our documentation. This was just a suggestion that we received.