How to Effectively Project Fields in MongoDB Documents Using the mongo-go-driver?

Project Fields in MongoDB Documents with Official mongo-go-driver

Filtering fields in MongoDB documents is crucial for selective data retrieval and performance optimization. To achieve this, the official mongo-go-driver provides flexible options.

Problem Statement:

Attempts to use the findopt.Projection method to suppress a field in a MongoDB document are unsuccessful. Despite specifying a projection using the fields struct, the field remains intact in the returned document.

Solution:

Root Cause: The fields struct used for projection is unable to access its fields due to unexported field names.

Remedy: Export the struct's field name and use struct tags to map it to the corresponding MongoDB field (_id in this case).

Here's the modified code:

type fields struct {
    ID int `bson:"_id"`
}

s := bson.NewDocument()
filter := bson.NewDocument(bson.EC.ObjectID("_id", starterId))

projection := fields{
    ID: 0,
}
result := staCon.collection.FindOne(
    nil, filter, options.FindOne().SetProjection(projection)).Decode(s)

Alternatively, you can use a bson.Document as the projection:

projection := bson.NewDocument(
    bson.EC.Int32("_id", 0),
)
result := staCon.collection.FindOne(
    nil, filter, options.FindOne().SetProjection(projection)).Decode(s)

By implementing these modifications, the desired field filtering will be achieved, resulting in a document with the _id field suppressed.

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