Loopback access both super model and extended models from same relation - loopbackjs

Question

I am using Loopback 3 and i have the following three models:
UserFile.json
{
"name": "UserFile",
"base": "PersistedModel",
"idInjection": true,
"options": {
"validateUpsert": true
},
"properties": {
"id": {
"type": "number",
"id": true,
"generated": true
},
"name": {
"type": "string",
"required": true
},
"size": {
"type": "number",
"default": 0
},
"uploadedAt": {
"type": "date",
"default": "$now"
}
},
"relations": {
"hasFile": {
"type": "hasMany",
"model": "UploadedFile",
"foreignKey": "fileId"
}
}
}
UploadedFile.json
{
"name": "UploadedFile",
"base": "PersistedModel",
"idInjection": true,
"options": {
"validateUpsert": true
},
"properties": {
"hashId": {
"type": "string",
"required": true
},
......
},
"relations": {
"file": {
"type": "belongsTo",
"model": "UserFile",
"foreignKey": "fileId"
}
}
}
PartitionedFile.json
{
"name": "PartitionedFile",
"base": "UploadedFile",
"idInjection": true,
"options": {
"validateUpsert": true
},
"properties": {
"partSize": {
"type": "number",
"default": 0
}
},
"relations": {
"file": {
"type": "belongsTo",
"model": "UserFile",
"foreignKey": "fileId"
}
}
}
The idea is that the UserFile has either one UploadedFile or (two or more) many PartitionedFile.
I want to be able to get from the UserFile, from the same relation the file, whether it is an UploadedFile or a PartitionedFile. Is it possible to achieve this just from the models' definitions or it can only be done with a remote method?

Answer 1

A relation from a model to another is bound to only one model; so you cannot have one relation called "file" to point to different models. In your example, it's bound to UploadedFile. In order for your model UserFile to have relations with both UploadedFile and PartitionedFile, you'll need two different relations.
For your UserFile to have either one UploadedFile or many PartitionedFile, it needs to have them both within its relations:
{
"name": "UserFile",
...
"relations": {
"uploadedFiles": {
"type": "hasOne", // Zero on one uploaded file
"model": "UploadedFile",
"foreignKey": "uploadedFileId"
},
"partitionedFiles": {
"type": "hasMany", // Zero or many partitioned files
"model": "PartitionedFile"
}
}
}
Then, to retrieve files from both UploadedFiles and PartitionedFiles through UserFile, you don't need a remote, but to include the models within your request.
For example, in ReactJS, it would look like this:
const response = await Axios.get(`/api/UserFile`, {
params: {
filter: {
include: [
{ relation: 'uploadedFiles' },
{ relation: 'partitionedFiles' },
]
}
}
}
Another solution would be to specify another model File that contains all these relations (UploadedFile, PartitionedFile, etc), so that the model UserFile can refer to the table File as one unique relation to retrieve the files...