How create mongodb aggregate query for multiple collections - mongodb

Question

I have two models
export const StorySchema = new Schema({
type: { type: String, required: true },
texts: { type: Array, require: true },
});
export const TextSchema = new Schema({
textKey: { type: String, required: true },
text: { type: String, required: true },
});
My collections
// stories
[
{
"type": "export",
"texts": ["export", "download"]
},
...
]
// Text
[
{
"textKey": "export",
"text": "Export ....."
},
{
"textKey": "download",
"text": "Download ....."
},
...
]
I want to combine a field textKey from collection text with array texts from collection story and write field text from collection text into result query. I have to get a array of object
[
{
"type": "export",
"texts": ["Export .....", "Download ....."]
},
...
]
I tried to create a aggregate multiple collections
public async getStoriesList(): Promise<Story[]> {
return await this.storyModel.aggregate([{
$lookup: {
from: 'texts',
localField: 'texts',
foreignField: 'textKey',
as: 'texts',
},
}]);
}
But i got an empty array. Where I made an error? How I can create a aggregate?

Answer 1

You can't lookup on an array, you could achieve what you want using this aggregation but it may be slow if you have big collections:
db.stories.aggregate([
{
"$unwind": "$texts"
},
{
"$lookup": {
"from": "texts",
"localField": "texts",
"foreignField": "textKey",
"as": "data"
}
},
{
"$unwind": "$data"
},
{
"$group": {
"_id": "type",
"texts": {
"$push": "$data.text"
}
}
},
{
"$project": {
"type": "$_id",
"_id": 0,
"texts": 1
}
}
])