use a variable value in lookup mongoose expression-CodePudding

I am using a mongoose model that brings documents and I add an aggregate to "join" with other collection. The real problem is when I use aggregate I cannot filter documents in the "original" collection (similar to findOne()). So when I use the aggregate function I get all documents but I just need 1.

i.e. (this is only an example for a point describe)


Collection A = {id,name,birthdate,dni} 
   Collection B = {avatar,dni.....} 
   a.aggregate([ '$lookup': {
       'from': 'avatars',
       'localField': 'dni',
       'foreignField': 'dni',
       'as': 'aditionalinfo' 
   } ])

this result in a full collection A additionalinfo object from B for each document but supposed to bring one person from collection A with the additional data (additionalinfo). I mean, I need to bring one document "joined" with the corresponding document from the other collection.

here is the last code I tried

let ley = await leyes.aggregate([
{         
 '$lookup': {           
   'from': 'digessituacion',           
   'localField': 'idsituacio',           
   'foreignField': 'idsituacio',            
   'as': 'situacion'        
 }       
}, {
   '$lookup': { 
      'from': 'digescategoria',            
      'localField': 'catego',            
      'foreignField': 'catego',            
      'as': 'categoria'         
    }
   }, 
{         
  '$match': { 
     'ley': 8996 // this is the number which I need to set variable cause is passed from params         
  }
}]);

this is the schema

    import { Schema, model } from "mongoose";
    const leyesSchema = new Schema(
      {
        ley: Number,
        resumen: String,
        notas: String,
        txtley: String,
        catego: String,
        detcatego: String,
        idsituacio: Number,
        promulgada: Date,
        sancionada: Date,
       
      },
      { timestamps: false, versionKey: false }
    );
    export default model("leyes", leyesSchema);

and the Schema of collection needed to "join"

    import { Schema, model } from "mongoose";
    const digessituacionSchema = new Schema(
      {
        idsituacio: Number,
        situacion: String,
      },
      { timestamps: false, versionKey: false }
    );
    export default model("digessituacion", digessituacionSchema);

if I put the number manually works but is not usable cause it must be a variable. Anyone knows the way for do this? It is possible?

CodePudding user response：

When the req.params is parsed, they are always parsed as type string. Since your ley field is of type number, you have to parse it first:

"$match": { 
  "ley": parseInt(req.params.ley, 10)     
}