11-grom-v2-05-initialization

1. FirstOrInit

Be careful ：
FirstOrInit It will only be assigned to the structure , Instead of writing to the table
FirstOrCreate Will be written into the table

1.1 Basic use

1.1.1 Instructions

Look up the table according to the parameters ,
find out , Then assign a value to the structure ;
We didn't find it , The structure can only get the value of the query condition .

db.FirstOrInit(&user, User{
    Name: "LiuBei"})

1.1.2 Complete example

• Code

package main

import (
	"database/sql"
	"fmt"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"time"
)

type User struct {
    
	ID int64
	Age int64
	Name string
	Email string
	Company string
}



func main() {
    
	db,sqlDB,_ := connect()
	defer sqlDB.Close()

	var user User
	db.FirstOrInit(&user, User{
    Name: "LiuBei"})
	fmt.Println(user)
}

func connect() (db *gorm.DB,sqlDB *sql.DB,err error) {
    
	dsn := "root:[email protected](127.0.0.1:3306)/crow?charset=utf8&parseTime=True&loc=Local"
	db, err = gorm.Open(mysql.Open(dsn), &gorm.Config{
    })
	sqlDB,_ = db.DB()
	if err != nil {
    
		fmt.Printf(err.Error())
		defer sqlDB.Close()
	}else {
    
		fmt.Printf("OK\n")
		sqlDB.SetMaxIdleConns(10)
		sqlDB.SetMaxOpenConns(100)
		sqlDB.SetConnMaxLifetime(time.Hour)
	}
	return
}

find out , Then assign the result to the structure ：

OK
{
    1 28 LiuBei [email protected] shu}

Not found , Then he only gets the value of the query condition ：

{
    0 0 LiuBei  }

1.2 Attrs （ If no result is found, give Struct assignment ）

1.2.1 Instructions

Attrs Written in FirstOrInit front , When FirstOrInit When no result is found , Will receive Attrs Parameter data of

db.Attrs(GuanYu).FirstOrInit(&user, User{
    Name: "GuanYu"})

1.2.2 Example

• Ideas
  Define a structure GuanYu, And the assignment , to Attrs call .
  Define a structure user to FirstOrInit Call to receive data .
  Define a structure , And the assignment , to FirstOrInit As a query condition .

• The process
  When FirstOrInit When finding the result , Will directly give the results to user.
  If we don't find , He can use Attrs Called GuanYu Structure , And assign value to user

• The original table

mysql> select * from users;
+----+----------+------+--------------------+---------+
| id | name     | age  | email              | company |
+----+----------+------+--------------------+---------+
|  1 | LiuBei   |   28 | [e-mail]   | shu     |
|  2 | GuanYu   |   22 | [e-mail]   | shu     |
|  3 | ZhangFei |   18 | [e-mail] | shu     |
+----+----------+------+--------------------+---------+
3 rows in set (0.00 sec)

• Code

func main() {
    
	db,sqlDB,_ := connect()
	defer sqlDB.Close()
    GuanYu := User{
    
    	ID: 3,
    	Name: "GuanYu",
    	Age: 22,
    	Email: "[email protected]",
    	Company: "shu",
	}

	var user User
	db.Attrs(GuanYu).FirstOrInit(&user, User{
    Name: "GuanYu"})
	fmt.Println(user)
}

• Output

Because I found Guan Yu , Then the information of Guan Yu is output

OK
{
    2 22 GuanYu [email protected] shu}

• If you don't find , Then you should enter the structure GuanYu As defined in Wu Sheng Information

OK
{
    0 99 WuSheng [email protected].com shen}

1.3 Assign（ Assign the parameter to whether it is found or not struct）

1.3.1 Instructions

• effect
  Assign Written in FirstOrInit front , No matter FirstOrInit Whether the data is found , Will receive Attrs Parameter data of

• Use
  Define a structure as Assign Parameters of , Cover FirstOrInit Some data found

• Examples

db.Where(xiShu{
    Name: "LiuBei"}).Assign(xiShu{
    Age: 35}).FirstOrInit(&user)

1.3.2 Example

• Code

func main() {
    
	db,sqlDB,_ := connect()
	defer sqlDB.Close()
    GuanYu := User{
    
    	Name: "WuSheng",
    	Company: "shen",
	}

	var user User
	db.Assign(GuanYu).FirstOrInit(&user, User{
    Name: "GuanYu"})
	fmt.Println(user)
}

• Check the output of the result

OK
{
    2 22 WuSheng [email protected].com shen}

• The output of the result cannot be found

OK
{
    0 0 WuSheng  shen}

2. FirstOrCreate

2.1 Basic use

2.1.1 Instructions

2.2.2 Example

• Code

func main() {
    
	db,sqlDB,_ := connect()
	defer sqlDB.Close()

	var user User
	db.FirstOrCreate(&user, User{
    Name: "ZhaoYun"})
	fmt.Println(user)
}

• Undetected output

OK
{
    31 0 ZhaoYun  }

• No data found , A record will still be added to the table

This data only receives query conditions

mysql> select * from users;
+----+----------+------+--------------------+---------+
| id | name     | age  | email              | company |
+----+----------+------+--------------------+---------+
|  1 | LiuBei   |   28 | [e-mail]   | shu     |
|  2 | GuanYu   |   22 | [e-mail]   | shu     |
|  3 | ZhangFei |   18 | [e-mail] | shu     |
| 31 | ZhaoYun  |    0 |                    |         |
+----+----------+------+--------------------+---------+
4 rows in set (0.00 sec)

• Check the output of the result

The result will be assigned to the received structure , No data will be added to the table .

OK
{
    31 18 ZhaoYun [email protected].com shu}

2.2 Attrs

• Use
  and FirstOrInit The method in is the same . Not found effective
• Examples

db.Attrs(ZhaoYun).FirstOrCreate(&user, User{
    Name: "ZhaoYun"})

2.3 Assign

• Use
  and FirstOrInit The method in is the same . Whether it is found or not covers the data in the table
• Examples

db.Assign(ZhaoYun).FirstOrCreate(&user, User{
    Name: "ZhaoYun"})