Why Are My mgo Queries Returning Empty Objects in Go?

The Mystery of Empty Objects in Go's Mgo

In the realm of Go API development, a common hurdle arises when working with MongoDB and the mgo package. Developers often encounter perplexing situations where queries return empty objects, leaving them baffled. To shed light on this enigma, let's delve into an example.

Consider a scenario where you'd like to interact with a MongoDB collection using the mgo package. After successfully connecting to the database, you execute a query to retrieve a user based on their username. However, to your dismay, the returned object remains devoid of any data.

The solution to this enigma lies in the use of BSON and JSON tags when defining your Go struct. Essentially, you need to ensure that the fields of your struct are exported, otherwise they will be ignored by the mgo package. To achieve this, simply prefix your fields with uppercase letters:

type users struct {
    User string `bson:"user" json:"user"`
    Data string `bson:"data" json:"data"`
}

By following this convention, you explicitly declare that the fields should be exported and accessible to the mgo package. Upon making this adjustment, the subsequent queries will no longer yield empty objects, allowing you to retrieve the data you seek from MongoDB.

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