Database
db={model_collection:[{"_id":ObjectId("63c2f9c25c76f3738a4b83f6"),"description":" ddd","name":" nameeee","owner_id":3,"fields":[{"field_id":"6c16c475-d5b7-4b79-b357-9eca0e5351aa","api_name":"a","name":"A","type":"Text"},{"field_id":"6c16c475-d5b7-4b79-b357-9eca0e5351ba","api_name":"b","name":"A","type":"Text"},{"field_id":"6c16c475-d5b7-4b79-b357-9eca0e5351bb","api_name":"c","name":"A","type":"Number"}]}],content_collection:[{"_id":"63c32a4e6a9a6ece4bbe81c8","fields":[{"content":"1","field_id":"6c16c475-d5b7-4b79-b357-9eca0e5351aa"},{"content":"33","field_id":"6c16c475-d5b7-4b79-b357-9eca0e5351ba"},{"content":1,"field_id":"6c16c475-d5b7-4b79-b357-9eca0e5351bb"}],"model_id":ObjectId("63c2f9c25c76f3738a4b83f6")},{"_id":"63c32ae06a9a6ece4bbe81c9","fields":[{"content":"1","field_id":"6c16c475-d5b7-4b79-b357-9eca0e5351aa"},{"content":99999,"field_id":"6c16c475-d5b7-4b79-b357-9eca0e5351bb"}],"model_id":ObjectId("63c2f9c25c76f3738a4b83f6")}]}
Query
db.model_collection.aggregate([{"$match":{"_id":ObjectId("63c2f9c25c76f3738a4b83f6")}},{"$project":{"_id":ObjectId("63c2f9c25c76f3738a4b83f6"),"result":{"$arrayToObject":{"$map":{"input":"$fields","as":"field","in":{"k":"$$field.field_id","v":"$$field"}}}}}},{"$lookup":{"from":"content_collection","localField":"_id","foreignField":"model_id","as":"content"}},{"$project":{"data":{"$map":{"input":"$content","as":"content_el","in":{"$map":{"input":"$$content_el.fields","as":"content_field","in":{"$mergeObjects":["$$content_field",{"$getField":{"field":{"$literal":"$$content_field.field_id"},"input":"$result"}}]}}}}}}}])