Golang, MongoDB alert error when using `$facet` operator-CodePudding

I set up my facet like that:

    metadataStage := bson.D{
        {"$facet", bson.D{
            {"metadata", bson.A{bson.D{
                {"$group", bson.D{
                    {"_id", nil},
                    {"total", bson.D{{"$sum", 1}}}}}}, // get number of documents that matches the all above conditions
            }},
            {"data", bson.A{bson.D{
                //{"$sort", sortStage}, // sort by field and direction
                {"$skip", skip}, // skip number of documents
                {"$limit", limit}}}}, // limit them
        }},
    }

but when I run my code, Mongo Driver always alerts the error A pipeline stage specification object must contain exactly one field.. I do not think that this is a syntax error. Please help me, thank you so much

CodePudding user response：

Each pipeline for the data facet should be element of an array

    metadataStage := bson.D{
        {"$facet", bson.D{
            {"metadata", bson.A{
                bson.D{{"$group", bson.D{
                    {"_id", nil},
                    {"total", bson.D{{"$sum", 1}}}}}}, // get number of documents that matches the all above conditions
            }},
            {"data", bson.A{
                //bson.D{{"$sort", sortStage}}, // sort by field and direction
                bson.D{{"$skip", skip}}, // skip number of documents
                bson.D{{"$limit", limit}}}}}, // limit them
        }}

Alternately, you could write to be clear that you are declaring stages of the pipeline for the facets.

    metadataStage := bson.D{
        {"$facet", bson.D{
            {"metadata", mongo.Pipeline{
                bson.D{{"$group", bson.D{
                    {"_id", nil},
                    {"total", bson.D{{"$sum", 1}}}}}}, // get number of documents that matches the all above conditions
            }},
            {"data", mongo.Pipeline{
                //bson.D{{"$sort", sortStage}}, // sort by field and direction
                bson.D{{"$skip", skip}},      // skip number of documents
                bson.D{{"$limit", limit}}}}}, // limit them
        }}