将struct / document插入mongo（通过mgo）时，将忽略JSON标签

This is what the struct looks like This is what the documents look like in Mongo.

If you look at the documentation of the mgo package, you will see the structs there are annotated with `bson:"fieldName` not `json:"fieldName"`. You can see an example here

The reason for this is that mongo uses the bson serialization format instead of json to send the structures over the wire. bson is very similar to json in what it can store, but it is a binary format, and is optimized for use in storage systems like a database.

So update your struct to look like so:

type Event struct {
    Id           string     `bson:"id"`
    CreationDate time.Time  `bson:"creationTime"`
    CreatorId    string     `bson:"creatorId"`
    Place        string     `bson:"place"`
    ActivityId   string     `bson:"activityId"`
    Time         time.Time  `bson:"time"`
    Lang         string     `bson:"lang"`
}

You can actually use both json and bson tags at the same time.

type Event struct {
    Id           string    `json:"id" bson:"id"`
    CreationDate time.Time `json:"creationTime" bson:"creationTime"`
    CreatorId    string    `json:"creatorId" bson:"creatorId"`
    Place        string    `json:"place" bson:"place"`
    ActivityId   string    `json:"activityId" bson:"activityId"`
    Time         time.Time `json:"time" bson:"time"`
    Lang         string    `json:"lang" bson:"lang"`
}