How to Embed a Struct in Another Struct with MongoDB in Golang Without Losing Data?

Embedding a Struct in Another Struct in Golang with MongoDB

In Golang, embedding a struct within another struct allows you to inherit fields from the embedded struct. However, you may encounter issues when working with embedded structs and MongoDB, potentially leading to the loss of embedded field data.

Understanding the Issue

Consider a scenario where you need to provide different JSON responses for a user resource based on the user role. One response includes a "Secret" field, which should only be displayed to admins.

In your current code, you have created separate structs for User and adminUser, with the latter containing the "Secret" field. However, embedding User into adminUser using inheritance (type adminUser struct { User; Secret string }) does not work as expected.

Solution

To resolve this issue, you can utilize the bson package's "inline" flag. By using bson:",inline", you can inline the fields of the embedded struct into the parent struct.

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

This approach allows you to access both fields of the User struct within the adminUser struct.

Additional Considerations

Note that using bson:",inline" can lead to duplicate key errors when reading from the database, as both structs contain the "Secret" field. To avoid this, it is recommended to remove the "Secret" field from the User struct and only include it in the adminUser struct. This ensures that the "Secret" field is only accessible through the adminUser struct, providing the desired level of control.

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