How to combine multiple update GORM MySql queries into 1?

Question

I have a MySQL table containing 4 columns

(A(primary key, int), B(string), C(string), D(string)).

I want to run an update query finding row using A, where I can update data of 1, 2, or all 3 columns(B, C, D). I get the data from the front-end in JSON format. Currently, I am checking the length of strings I get in input, and if they are >0, I update those columns one by one. So in the worst case, I will be running 3 SQL updates. Is there a way to do this in 1 SQL query using GORM, and Golang?

Example JSON structure
{
A: 23,
B: "word1",
D: "word2"
}

In this case, I only want to update columns B and D.

I will unmarshal this using a Golang structure which will be of the form

type rating struct{
    A int,
    B string,
    C string,
    D string
        }

So in Golang value of C will be an empty string.

var rating_var rating
if len(rating_var.B)>0{
       db.Model(&ratings).where("A=?",rating_var.A).Update(map[struct]interface{}{"B": rating_var.B})
        }

if len(rating_var.C)>0{
       db.Model(&ratings).where("A=?",rating_var.A).Update(map[struct]interface{}{"C": rating_var.C})
        }

if len(rating_var.D)>0{
       db.Model(&ratings).where("A=?",rating_var.A).Update(map[struct]interface{}{"D": rating_var.D})
        }

Is there a way to do this in 1 SQL query using GORM, and Golang?

Answer 1

I would suggest to build a Model according to your conditions first. Use that model to run only one SQL query. Check the complete example on playground here .

Note that gorm will take care of some missing fields. Now if the rating.C is blank, gorm will not update the value of c column in record.

        rating := Rating{
                A: 1,
                B: "b1",
                D: "d2",
        }

        var toUpdate RatingModel
        if len(rating.B) > 0 {
                toUpdate.B = rating.B
        }

        if len(rating.C) > 0 {
                toUpdate.C = rating.C
        }

        if len(rating.D) > 0 {
                toUpdate.D = rating.D
        }
        db.Model(&toUpdate).Where("A=?", rating.A).Updates(toUpdate)

I would suggest using structs over map. Go is strongly typed language thus using structs is more idiomatic.

Answer 2

You can use Updates to update multiple fields.

db.Model(&user).Updates(User{Name: "hello", Age: 18, Active: false})

db.Model(&ratings).where("A=?",rating_var.A).Updates(map[struct]interface{}{"B": rating_var.B, "C": rating_var.C})

Updates