How to Avoid the \'Can\'t Marshal interface {} as a BSON document\' Error in Go?

How to Construct and Pass BSON Documents in Go Lang?

Introduction

MongoDB interacts with documents represented in Binary JSON (BSON) format. In Go, constructing and passing BSON documents for insertion into MongoDB can be challenging. This article will provide a solution to the common error encountered during this process.

The Error: Interface{} Cannot Marshal as BSON Document

When passing a BSON document to a function parameter defined as interface{}, an error may occur: "Can't marshal interface {} as a BSON document." This error indicates that Go cannot automatically marshal an arbitrary interface as a BSON document.

Solution: Use a Custom Struct

To resolve this issue, avoid using interface{} and instead define a custom struct to represent the BSON document. For example, consider the following BSON document:

{
  "_id": "53439d6b89e4d7ca240668e5",
  "balanceamount": 3,
  "type": "reg",
  "authentication": {
    "authmode": "10",
    "authval": "sd",
    "recovery": {
      "mobile": "sdfsd",
      "email": "email@protected.com"
    }
  },
  "stamps": {
    "in": "x",
    "up": "y"
  }
}

In Go, the corresponding custom struct would be:

type Account struct {
  Id bson.ObjectId `bson:"_id"`
  BalanceAmount int
  // Other fields...
}

Pass the Custom Struct to Insert Function

Now, in the dbEngine.go file, modify the Insert function to accept the custom struct as an argument:

func Insert(document *Account) {
  // Connect to MongoDB and insert the document
}

Usage in the Application

To use this function, create an instance of the Account struct, populate its fields, and pass it to the Insert function:

acc := Account{
  Id: bson.NewObjectId(),
  BalanceAmount: 3,
  // Other fields...
}

dbEngine.Insert(&acc)

Conclusion

By creating a custom struct to represent the BSON document and passing it to a function that accepts the specific struct type, the error can be avoided, and BSON documents can be constructed and passed seamlessly.

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