How Can I Use Different Field Names for MongoDB and JSON Encoding in Go Structs?

Overcoming Limitations in Struct Tagging for MongoDB and JSON Encoding

When accessing data from a MongoDB database and subsequently encoding it to JSON, you may encounter a challenge if you wish to use different field names for each format. For instance, while MongoDB may require a field named "pageId," you may prefer to encode it as "pageId" in JSON.

Multiple Tag Definition: A Misunderstood Endeavor

Your initial attempt to define multiple name tags for a struct resulted in failure. You attempted to use commas as tag string separators:

type Page struct {
    PageId string                 `bson:"pageId",json:"pageId"`
    Meta   map[string]interface{} `bson:"meta",json:"pageId"`
}

However, this approach is incorrect.

The Path to Success: Unleashing the Power of Space

To successfully define multiple name tags in a struct, you must use spaces as tag string separators. Here's how it should be done:

type Page struct {
    PageId string                 `bson:"pageId" json:"pageId"`
    Meta   map[string]interface{} `bson:"meta" json:"meta"`
}

Understanding the Rationale

The documentation for the reflect package clearly states that tag strings should consist of non-empty strings with key-value pairs. Each key-value pair is separated by a space, and values are quoted using Go string literal syntax.

Each value is quoted using U+0022 '"' characters and Go string literal syntax.

By following this convention, you can effectively define multiple name tags for your struct and achieve the desired encoding behavior.

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