how to update one table with the _id from another table in Mongodb - mongodb

Question

I exported data from a MySQL database into JSON and imported it into MongoDB. The problem:
When I imported clients, MongoDB created its own _id field (I know this is built in functionality, but MySQL used a clientID, autoincrementing integer).
SO, when I imported my appointments collection, the clientID was renamed oldClientID. I'd like the clientID field to be the ObjectID of the corresponding client.
My schemas:
const apptSchema = new mongoose.Schema({
ID: Number,
clientID: {
type: mongoose.Schema.Types.ObjectId,
ref: 'Client'
},
oldClientID: Number,
...other field data
});
const clientSchema = new mongoose.Schema({
ID: Number,
familyID: Number,
first: String,
last: String,
});
Sample Patient Data:
{
"_id" : ObjectId("5d82240f7c8ddd03b62aee6a"),
"ID" : 18,
"familyID" : 6,
"first" : "Jane",
"last" : "Doe"
}
Sample Appointment Data
{
"_id" : ObjectId("5d82c8b95627367d122087f9"),
"ID" : 1885,
"oldPatientID" : 18,
"scheduled" : ISODate("2015-08-05T11:20:00Z"),
"note" : ""
},
{
"_id" : ObjectId("5d82c8b95627367d122088a8"),
"ID" : 2066,
"oldPatientID" : 18,
"scheduled" : ISODate("2015-09-17T16:00:00Z"),
"note" : ""
}
What appointments should look like:
{
"_id" : ObjectId("5d82c8b95627367d122087f9"),
"ID" : 1885,
"clientID": ObjectId("5d82240f7c8ddd03b62aee6a"),
"oldPatientID" : 18,
"scheduled" : ISODate("2015-08-05T11:20:00Z"),
"note" : ""
},
{
"_id" : ObjectId("5d82c8b95627367d122088a8"),
"ID" : 2066,
"clientID" : ObjectId("5d82240f7c8ddd03b62aee6a"),
"oldPatientID" : 18,
"scheduled" : ISODate("2015-09-17T16:00:00Z"),
"note" : ""
}
I am open to learning how to achieve this in the mongo shell or using mongoose in express (or if there is another cool way, like in Robo3T).

Answer 1

MongoDB will always use _id as the primary key, this behavior cannot be overwritten, though you can use the _id with values from your custom id. Though this might be confusing, it is better to use indexing on your custom id, and you don't need to use ObjectId for the custom index field, but can use your own custom id schema, like UUID or an incrementing integer value etc. though it has to be generated/incremented by you or some framework, like JPA
Check Indexes
For Mongoose, you can do;
new mongoose.Schema({
customId: { type: Number, index: true }
...other field data
});
with index: true

Answer 2

Ok, this worked out for me, although I'm sure there has to be an easier way:
db.getCollection("appts").aggregate(
[
{
"$lookup" : {
"from" : "clients",
"localField" : "clientID",
"foreignField" : "ID",
"as" : "CLIENT"
}
},
{
"$lookup" : {
"from" : "appttypes",
"localField" : "type",
"foreignField" : "ID",
"as" : "TYPE"
}
},
{
"$lookup" : {
"from" : "apptstatuses",
"localField" : "status",
"foreignField" : "ID",
"as" : "STATUS"
}
},
{
"$project" : {
"_id" : "$_id",
"clientID" : "$CLIENT._id",
"scheduled" : "$scheduled",
"note" : "$note",
}
},
{
"$out" : "apptslinked"
}
]
);
Then I exported that as JSON, dropped the appts table, and did a mongoimport using that file.