Get data from two different struct

Have this struct of User and Post and I try to make Name from User to be included within Post Struct when a user create a new post.

type User struct {
	ID             int
	Name           string
	Created        time.Time
}

type Post struct {
	ID int
	PostTitle string
	PostDesc string
	Created time.Time
}

How can I create something connected between this two struct such as Author of the Post ?

The goal is try to get the name of the post author which from User struct with the code below:

post, err := app.Models.Posts.GetPost(id)

GetPost() just run SELECT query and scan row

Give it a try to this solution, maybe it resolves your issue.

First, I defined the structs in this way:

// "Post" belongs to "User", "UserID" is the foreign key
type Post struct {
	gorm.Model
	ID        int
	PostTitle string
	PostDesc  string
	Created   time.Time
	UserID    int
	User      User
}

type User struct {
	ID      int
	Name    string
	Created time.Time
}

In this way, you can say that Post belongs to User and access the User's information within the Post struct.
To query the records, you've to use Preload("User") to be sure to eager load the User records from the separate table.
> Keep attention to the name you pass in as the argument in Preload, as it can be tricky.

Lastly, you'll be able to access data in the embedded struct (with the dot notation).
Below, you can find a complete working example (implemented with the use of Docker):

package main

import (
	"fmt"
	"time"

	"gorm.io/driver/postgres"
	"gorm.io/gorm"
)

// "Post" belongs to "User", "UserID" is the foreign key
type Post struct {
	gorm.Model
	ID        int
	PostTitle string
	PostDesc  string
	Created   time.Time
	UserID    int
	User      User
}

type User struct {
	ID      int
	Name    string
	Created time.Time
}

func main() {
	dsn := "host=localhost user=postgres password=postgres dbname=postgres port=5432 sslmode=disable"
	db, err := gorm.Open(postgres.Open(dsn), &gorm.Config{})
	if err != nil {
		panic(err)
	}

	db.AutoMigrate(&Post{})

	newPost := &Post{ID: 1, PostTitle: "Golang", PostDesc: "Introduction to Golang", Created: time.Now(), UserID: 1, User: User{ID: 1, Name: "John Doe", Created: time.Now()}}
	db.Create(newPost)

	var post Post
	db.Preload("User").Find(&post, 1)
	fmt.Printf("author name: %q\n", post.User.Name)
}

Let me know if I answered your question!

This approach is without any ORM.
It's a simple query that can return multiple rows. You've to scan the whole resultset and map each column on the struct's fields.
> Keep in mind to always check for errors.

Below you can find the solution:

package main

import (
	"database/sql"
	"fmt"
	"time"

	_ "github.com/lib/pq"
)

type Post struct {
	ID        int
	PostTitle string
	PostDesc  string
	Created   time.Time
	UserID    int
	User      User
}

type User struct {
	ID      int
	Name    string
	Created time.Time
}

func main() {
	conn, err := sql.Open("postgres", "host=localhost user=postgres password=postgres dbname=postgres port=5432 sslmode=disable")
	if err != nil {
		panic(err)
	}
	defer conn.Close()

	// get MAX id
	var id int
	conn.QueryRow(`SELECT MAX(id) FROM posts`).Scan(&id)

	// insert
	sqlInsertStmt := `INSERT INTO posts (id, post_title, post_desc, created, user_id) VALUES ($1,$2,$3,$4,$5)`
	if _, err = conn.Exec(sqlInsertStmt, id+1, "TDD", "Introduction to Test-Driven-Development", time.Now(), 1); err != nil {
		panic(err)
	}

	// read
	rows, err := conn.Query(`SELECT posts.id, post_title, post_desc, posts.created, users.id, users.name, users.created FROM posts INNER JOIN users ON posts.user_id=users.id`)
	if err != nil {
		panic(err)
	}

	var posts []Post
	for rows.Next() {
		var post Post
		if err = rows.Scan(&post.ID, &post.PostTitle, &post.PostDesc, &post.Created, &post.User.ID, &post.User.Name, &post.User.Created); err != nil {
			panic(err)
		}
		posts = append(posts, post)
	}

	if err = rows.Err(); err != nil {
		panic(err)
	}

	for _, v := range posts {
		fmt.Printf("author name: %q\n", v.User.Name)
	}
}

Let me know if this helps.

Edit

I've also included an example of INSERT in Postgres. To achieve it, we've to use the db.Exec() function, and provide the parameters.
> Pay attention to how you construct the query as you can get a SQL-Injection vulnerability.

Lastly, in a real-world scenario, you shouldn't lookup for the MAX id in the posts table but should be automatically generated.