Update method does not update zero value

问题

Original Question

When using the Update method in GORM the new data does not get saved. i.e. I want to set a bool from true to false, but it stays true even after the Update method.

In the description of the method there is a warning: "WARNING when update with struct, GORM will not update fields that with zero value"

Since I am using a struct to update and false is the zero value of bool, this seems expected behaviour, but I don't see any reason why to do so and how to overcome this.

func UpdateData(c *fiber.Ctx) error {
    db := database.DBConn

    data := new([]entities.Data)

    if err := c.BodyParser(&data); err != nil {
        return err
    }

    db.Update(&data)
    return c.JSON(data)
}

Solution Summary

First, as suggested I left out the new keyword when instantiating the structs. Then, I used a helper function (from here) for converting a struct to map while keeping the json alias as keys:

// StructToMap Converts a struct to a map while maintaining the json alias as keys
func StructToMap(obj interface{}) (newMap map[string]interface{}, err error) {
    data, err := json.Marshal(obj)

    if err != nil {
        return
    }

    err = json.Unmarshal(data, &newMap) // Convert to a map
    return
}

Then I loop over each element in the data slice in order to convert it and update it one by one:

func UpdateData(c *fiber.Ctx) error {
    db := database.DBConn

    data := []entities.Dard{}

    if err := c.BodyParser(&data); err != nil {
        return err
    }

    for _, record := range data {
        mappedData, _ := StructToMap(record)
        db.Model(&entities.Data{}).Update(mappedData)
    }

    return c.JSON(data)
}

*Error handling is obviously reduced in this example.

回答1:

From official doc

NOTE When update with struct, GORM will only update non-zero fields, you might want to use map to update attributes or use Select to specify fields to update

So use map[string]interface{} to update non-zero fields also. Example:

db.Model(&user).Updates(map[string]interface{}{"name": "hello", "age": 18, "actived": false})

As you have struct already you can convert struct into map[string]interface{} (See details about conversion) then update. Another way is change the type of field as pointer.

来源：https://stackoverflow.com/questions/64330504/update-method-does-not-update-zero-value

标签

go-gorm

go-fiber