Update Mongodb fields with omitempty flag in Golang structure

[Amandeep Kaur]

Hi I am working on a Coupon form in which I have some optional fields. Introduction: All the form field values are received as JSON and mapped into a Golang structure. In the structure, I have added an "omitempty" flag with every field. So only those form values are mapped which have some appropriate value, rest of the values like 0, " ", false are ignored by the structure. Here is the Golang structure 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"` } Problem: When I save this form for the very first time, the form values that are appropriate are saved into the Mongodb. Now I want to update that form and suppose there is a check box, which was checked at the time of saving data. While updating form, the checkbox is unchecked and form is submitted to save. Now as I have applied "omitempty" flag in the structure, so its not mapping the empty value to the checkbox field. Since the value is not mapped into the structure, its not getting saved into the Database. When a user edits the form for the second time, it sees the same check box as checked. (But practically, the value should be updated to the DB and the check box should be displayed as unchecked.) I am using the same form data (in JSON format) in a REST API. In API, while updating form data, if I mention only those values which are required and don't pass the values which I don't want to update, then MongoDB is overriding the whole document with the provided required values(Even those values are also being overridden which I don't want to update as well as don't pass in the API). Requirement: In future, I want to expose the REST API, So I don't want this thing to be happened there. That is why I don't want to remove "omitempty" flag from the structure fields. Is there any way to save the empty form values or API data fields to the DB while using omitempty flag in the structure? Thanks!

[Diego Medina]

replied on the mgo list 

https://groups.google.com/d/topic/mgo-users/F3LbWdyPGDc/discussion

(pasted here to save a click)

Hi,

> the checkbox is unchecked and form is submitted to save. Now as I have applied "omitempty" 

if the checkbox is unchecked, your client side code should send "false" to the go server, so omitempty is not applied because it is not empty, it is false, so saving it to mongo will actually update the field.

for truly optional fields, what I do is, declare the fields as pointers to the type, so, you would have

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"`// I assume this is also optional

    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"`

}

the bson/json Un/marshaller will then omit the values that are nil pointers, so now yo ucan tell the difference between a false checkbox, and a REST POST that did not include the field at all

Hope this helps.

Diego

[Amandeep Kaur]

Thanks @Diego Medina  It worked for me.