How to Preserve Empty Values in MongoDB Updates Using Golang\'s `omitempty`?

How to Handle Empty Values in MongoDB Updates with "omitempty" in Golang Structures

Introduction

Golang structures with "omitempty" fields allow for mapping selective JSON values into the structure, excluding fields with empty values. However, this can lead to challenges when updating MongoDB documents, as empty values may not be reflected in the database.

Problem

When using a structure with "omitempty" flag to map JSON form values, empty fields are ignored. This poses issues when updating documents in MongoDB:

• If a previously checked checkbox is unchecked during update, the empty value is not mapped into the structure and cannot be saved to the database.
• Conversely, in REST API updates, providing only necessary values can override other field values in the database, even those that shouldn't be changed.

Requirement

Maintaining the "omitempty" flag while preserving the ability to save empty or updated values in MongoDB is essential for a flexible and robust update process.

Solution

To resolve this issue, convert the affected fields in the structure to pointers:

type Coupon struct {
    Id               *int    `json:"id,omitempty" bson:"_id,omitempty"`
    Name             string `json:"name,omitempty" bson:"name,omitempty"`
    Code             string `json:"code,omitempty" bson:"code,omitempty"`
    Description      string `json:"description,omitempty" bson:"description,omitempty"`
    Status           *bool   `json:"status" bson:"status"`
    MaxUsageLimit    *int    `json:"max_usage_limit,omitempty" bson:"max_usage_limit,omitempty"`
    SingleUsePerUser *bool   `json:"single_use_per_user,omitempty" bson:"single_use_per_user,omitempty"`
}

This way:

• A nil pointer represents an omitted field.
• A non-nil pointer to a zero value represents an empty field.
• A non-nil pointer to a non-zero value sets the field to the specified value.

By using pointers, we enable the flexibility to handle both empty and updated values in MongoDB updates while retaining the "omitempty" behavior.

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