如何使用 GORM 创建或更新记录?

问题描述

Gorm 有一个 FirstOrCreate 方法和一个 FirstOrInit 但是之后如何检查记录是否实际创建?我喜欢创建一个记录，如果它不存在，如果存在我想更新一些字段.

Gorm has a FirstOrCreate method and a FirstOrInit but how to check afterwards if the record was actually created? I like to create a record if it does not exists and if it exists I want to update some fields.

推荐答案

update 2020.10.09

update 2020.10.09

感谢@vaelin

从 1.20.x 开始，GORM 为不同的数据库提供兼容的 Upsert 支持(Upsert-关于冲突)

From 1.20.x on, GORM provides compatible Upsert support for different databases( Upsert-On-Conflict)

// Update columns to new value on `id` conflict
DB.Clauses(clause.OnConflict{
  Columns:   []clause.Column{{Name: "id"}}, // key colume
  DoUpdates: clause.AssignmentColumns([]string{"name", "age"}), // column needed to be updated
}).Create(&users)
// MERGE INTO "users" USING *** WHEN NOT MATCHED THEN INSERT *** WHEN MATCHED THEN UPDATE SET "name"="excluded"."name"; SQL Server
// INSERT INTO "users" *** ON CONFLICT ("id") DO UPDATE SET "name"="excluded"."name", "age"="excluded"."age"; PostgreSQL
// INSERT INTO `users` *** ON DUPLICATE KEY UPDATE `name`=VALUES(name),`age=VALUES(age); MySQL

使用 gorm 1.9.x 或以下版本，先更新，然后在不存在时插入更有效.

With gorm 1.9.x or below, it's more effecient to update first, then insert when not existed.

// update only set name=nick
if err := db.Model(&newUser).Where("id = ?", 3333).Update("name", "nick").Error; err != nil {
    // always handle error like this, cause errors maybe happened when connection failed or something. 
    // record not found...
    if gorm.IsRecordNotFoundError(err){
        db.Create(&newUser)  // create new record from newUser
    }
}

FirstOrInit 和 FirstOrCreate 是不同的.如果数据库中没有匹配记录，FirstOrInit 将初始化结构体但不创建记录，FirstOrCreate 将创建一个记录并将该记录查询到结构体中.

FirstOrInit and FirstOrCreate are different. If there is no match record in database, FirstOrInit will init struct but not create record, FirstOrCreate will create a record and query that record to struct.

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