How to Include Embedded Struct Fields in JSON Response with MongoDB in Golang?

Embedding Structs in Golang with MongoDB

In Golang, embedding structs is a technique to extend the functionality of a struct by nesting it within another struct. However, when it comes to working with embedded structs and MongoDB, certain challenges may arise.

The Problem: Excluding Nested Fields from JSON Response

Consider the following User struct:

type User struct {
  Id      bson.ObjectId `json:"id,omitempty" bson:"_id,omitempty"`
  Name    string        `json:"name,omitempty" bson:"name,omitempty"`
  Secret  string        `json:"-,omitempty" bson:"secret,omitempty"`
}

The Secret field is excluded from the JSON representation using json:"-". This is useful in most cases where the secret information should not be disclosed.

The Dilemma: Admin Routes and Embedded Structs

To provide admins with access to the secret field, an adminUser struct is created, which includes the User struct as an embedded field:

type adminUser struct {
  User
  Secret  string        `json:"secret,omitempty" bson:"secret,omitempty"`
}

However, this approach only returns the Secret field, as the embedded User fields are ignored.

The Solution: bson Inline Flag

To resolve this issue, the bson package provides an inline flag that allows the inclusion of embedded fields in JSON serialization and MongoDB document decoding.

type adminUser struct {
    User    `bson:",inline"`
    Secret  string `json:"secret,omitempty" bson:"secret,omitempty"`
}

With this modification, both the User fields (excluding Secret) and the Secret field in adminUser will be included in the JSON response and MongoDB document.

Alternative Approach

Alternatively, one could consider removing the Secret field from the User struct and only include it in the adminUser struct. This simplifies the data model and ensures that secrets are only written to and read from the database by authorized administrators.

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