How to deal with null values ​​in golang?

php editor Yuzai introduces to you how to handle null values ​​in golang. In golang, a null value usually means that the variable has not been assigned a value or has no valid value. To handle null values, golang provides multiple methods. First, you can use a conditional statement (if statement) to check if a variable is nil. Secondly, you can initialize the variable with a default value to ensure that the variable is not empty. In addition, you can also use a zero value instead of a null value. For example, for a numeric type variable, the zero value is 0; for a string type variable, the zero value is an empty string. You can also use pointers to handle null values ​​and determine whether a variable is null by judging whether the pointer is nil. In addition, golang also provides some special data types, such as slices, maps, and channels, which default to nil when declared, and can handle null values ​​by determining whether they are nil. In short, golang provides a variety of flexible ways to handle null values, and developers can choose the appropriate method to handle null values ​​based on specific scenarios.

Question content

User model

type userexample struct {
    id       primitive.objectid `json:"id,omitempty"`
    name     string             `json:"name,omitempty"`
    location string             `json:"location,omitempty"`
    title    string             `json:"title,omitempty"`
}

Update user

func updateuserexample() gin.handlerfunc {
    return func(c *gin.context) {
        ctx, cancel := context.withtimeout(context.background(), 10*time.second)
        userid := c.param("userid")
        var user models.userexample
        defer cancel()
        objid, _ := primitive.objectidfromhex(userid)

        //validate the request body
        if err := c.bindjson(&user); err != nil {
            c.json(http.statusbadrequest, responses.userresponseexample{
                status:  http.statusbadrequest,
                message: "error",
                data: map[string]interface{}{
                    "data": err.error()},
            })
        }

        update := bson.m{
            "name":     user.name,
            "location": user.location,
            "title":    user.title,
        }
        result, err := usercollectionexample.updateone(ctx, bson.m{
            "id": objid,
        }, bson.m{
            "$set": update,
        })
        if err != nil {
            c.json(http.statusinternalservererror, responses.userresponseexample{
                status:  http.statusinternalservererror,
                message: "error",
                data: map[string]interface{}{
                    "data": err.error(),
                }})
            return
        }

        //get update userexample detail
        var updateuser models.userexample
        if result.matchedcount == 1 {
            err := usercollectionexample.findone(ctx, bson.m{
                "id": objid,
            }).decode(&updateuser)
            if err != nil {
                c.json(http.statusinternalservererror, responses.userresponseexample{
                    status:  http.statusinternalservererror,
                    message: "error",
                    data: map[string]interface{}{
                        "data": err.error(),
                    }})
                return
            }
        }
        c.json(http.statusok, responses.userresponseexample{
            status:  http.statusok,
            message: "success",
            data: map[string]interface{}{
                "data": updateuser,
            },
        })
    }
}

I tried updating the data via postman but if value == null it will be removed from the collection

In this case, I want to update the user's title, before updating all the data is already there

Postman

{
    "title": "user one"
}

It's working on changing the title in the collection. However, other data (name and location) have disappeared

"data": {
            "id": "63d2ac86aeb9d78d3d5daf21",
            "title": "User One",
        }

So, how to deal with null values ​​in the request body?

I only want to change the title of this case

Workaround

Normally, such partial updates are handled using a structure like this:

type userupdaterequest struct {
    id       primitive.objectid `json:"id,omitempty"`
    name     *string             `json:"name,omitempty"`
    location *string             `json:"location,omitempty"`
    title    *string             `json:"title,omitempty"`
}

Pay attention to pointers. This way, API callers can send non-zero values ​​for the fields they want to update. It can also use an empty string to set the field value to null.

Then on the database side you have to create an update statement:

updateFields:=bson.M{}
if request.Name!=nil {
   updateFields["name"]=*request.Name
}
if request.Location!=nil {
   updateFields["location"]=*request.Location
}
// etc.
update:=bson.M{"$set":updateFields}

Then use update to update the database record.

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