How are composite ids working in Loopback? - mongodb

Question

I am trying to implement composite ids with Loopback 3.0.0 using MongoDB. each pair of product_id/keyword should be unique...
I check the official documentation:
https://loopback.io/doc/en/lb3/Model-definition-JSON-file.html#data-mapping-properties
Here my model:
{
"name": "comparative",
"plural": "comparative",
"base": "PersistedModel",
"idInjection": true,
"options": {
"validateUpsert": true
},
"properties": {
"product_id": {
"id": true,
"type": "string",
"required": true
},
"keyword": {
"id": true,
"type": "string",
"required": true
}
},
"validations": [],
"relations": {},
"acls": [],
"methods": {}
}
Although, all my attempts to make composite ids of product_id/keyword failed.
When I POST:
// 1st POST Success.
{
"product_id": "string",
"keyword": "string"
}
// 2nd POST Success.
{
"product_id": "string1",
"keyword": "string"
}
// 3rd POST FAILED -> I want it to success
{
"product_id": "string",
"keyword": "string1"
}
Any ideas?
Even after that, I need to keep an auto-generated MongoDB id just to keep track of the objects.
I tried with "idInjection", not working along with composite ids... (not generating anything...)
If I add another field "id" with generated set to true, composite ids doesn't work at all (contrary as before where it worked partially)
Thank you,

Answer 1

You can declare a composite index between product_id and keyword:
https://loopback.io/doc/en/lb3/Model-definition-JSON-file.html#indexes
{
"name": "comparative",
"plural": "comparative",
"base": "PersistedModel",
"idInjection": true,
"options": {
"validateUpsert": true
},
"properties": {
"product_id": {
"type": "string",
"required": true
},
"keyword": {
"type": "string",
"required": true
}
},
"validations": [],
"relations": {},
"acls": [],
"methods": {},
"indexes": {
"productid_keyword_index": {
"keys": {
"product_id": 1,
"keyword": -1
},
"options": {
"unique": true
}
}
}
}

Answer 2

You don't have to put id: true in the properties. This is done only to a single field, if you don't want the default identification ie. _id in mongo
"properties": {
"product_id": {
"type": "string",
"required": true
},
"keyword": {
"type": "string",
"required": true
}
}
I assume that you have another model Product to which you want relate this model. In order to achieve this, add relations
check this loopback documentation to do so.
Hope this helped