禁用Go mongo bson地图中的某些字段

Question

我用的是"go.mongodb.org/mongo-driver/bson"

是否有一种方法可以禁用一个字段，但仍然是一个有效的bson映射？

publishFilter := bson.M{}

if publishedOnly {
    publishFilter = bson.M{"published": true}
}

pipeline := []bson.M{
    {"$sort": bson.M{"_id": -1}},
    {
        "$match": bson.M{
            "_id": bson.M{
                "$gt":  sinceObjectID,
                "$lte": maxObjectID,
            },
            publishFilter, // I want to control this to be nothing or `{"published": true}`
            // depending on `publishedOnly`
        },
    },
    {"$limit": query.Count},
}

这个片段绝对不会编译Missing key in map literal

Answer 1

不能“禁用”映射中的字段，但可以有条件地构建$match文档：

matchDoc := bson.M{
    "_id": bson.M{
        "$gt":  sinceObjectID,
        "$lte": maxObjectID,
    },
}

if publishedOnly {
    matchDoc["published"] = true
}

pipeline := []bson.M{
    {"$sort": bson.M{"_id": -1}},
    {"$match": matchDoc},
    {"$limit": query.Count},
}