douyi2798 2018-11-02 14:08
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How can I filter fields with the mongo-go-driver. Tried it with findopt.Projection but no success.

type fields struct {
    _id int16

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

var opts []findopt.One
opts = append(opts, findopt.Projection(fields{
    _id: 0,

staCon.collection.FindOne(nil, filter, opts...).Decode(s)

In the end, I want to suppress the field "_id". But the documents didn't change.

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  • duanchou6534 2018-11-05 13:54

    The reason why it doesn't work for you is because the field fields._id is unexported, and as such, no other package can access it (only the declaring package).

    You must use a field name that is exported (starts with an uppercase latter), e.g. ID, and use struct tags to map it to the MongoDB _id field like this:

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

    And now to perform a query using a projection:

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

    Note that you may also use a bson.Document as the projection, you don't need your own struct type. E.g. the following does the same:

    projection := bson.NewDocument(
        bson.EC.Int32("_id", 0),
    result := staCon.collection.FindOne(
        nil, filter, options.FindOne().SetProjection(projection)).Decode(s)
    本回答被题主选为最佳回答 , 对您是否有帮助呢?



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