CODEWITHSUNDEEP
mongodbgo
Rajandeep Kaur
Rajandeep Kaur

Reputation: 185

Cursor option required

I am using Go and MongoDB for my Project.I used

db.collection.aggregate([{$match:{}},{$lookup:{}},{$addFields:{}}])

it is working fine in MongoDB, but when I use pipeline in Go, it gives below error

The 'cursor' option is required, except for aggregate with the explain argument

Go code is

matchStage:=bson.M{"$match":bson.M{}}
pipeline := collection.Pipe([]bson.M{matchStage})
    err = pipeline.All(&resp)

Upvotes: 1

Views: 330

Answers (1)

hhharsha36
hhharsha36

Reputation: 3349

This is not how you are supposed to implement Mongo-Aggregation query in Go.

It should be of the format

cursor, err := collection.Aggregate(
        ctx,
        mongo.Pipeline{<PIPELINE-STAGES>},
        options.Aggregate().SetAllowDiskUse(true),
        )

Hence your code should be:

ctx, _ = context.WithTimeout(context.Background(), 2*time.Second)

matchStage := bson.D{
        {"$match", bson.D{}},
    }
lookupStage := bson.D{
        {"from", ""},
        {"let": bson.D{{}}},
        {"pipeline": bson.A{}},
        {"as": ""},
    }
addFieldsStage := bson.D{
        {"$addFields", bson.D{}},
    }

cursor, err := collection.Aggregate(
    ctx,
    mongo.Pipeline{matchStage, lookupStage, addFieldsStage},
    options.Aggregate().SetAllowDiskUse(true),  // Mongo-Aggregate options if any
    )
if err != nil {
    panic(err)
}

for cursor.Next(ctx) {
    var cursorResult bson.M
    err := cursor.Decode(&cursorResult)  // I world recommend to decode it using a struct instead
    if err != nil {
        panic(err)
    }

    fmt.Printf("Decoded Cursor: %v", cursorResult)
}

err = cursor.Close(ctx)
if err != nil {
  panic(err)
}

Note: I haven't tested the code in my local. So let me know in case of errors.

Upvotes: 1

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