Fetch Data using One To Many Relationship in GORM

Install Libraries

Make sure Git is installed on your machine and in your system’s PATH. Install the package to your $GOPATH with the go tool from shell:

$ go get github.com/go-sql-driver/mysql
$ go get -u github.com/jinzhu/gorm

Create Database

Create a database with the name is learngorm. This database have 1 tables: Product table.

--
-- Table structure for table `faculty`
--

CREATE TABLE `faculty` (
  `id` int(11) NOT NULL PRIMARY KEY AUTO_INCREMENT,
  `name` varchar(250) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

--
-- Dumping data for table `faculty`
--

INSERT INTO `faculty` (`name`) VALUES
('Faculty 1'),
('Faculty 2'),
('Faculty 3');

--
-- Table structure for table `student`
--

CREATE TABLE `student` (
  `id` int(11) NOT NULL PRIMARY KEY AUTO_INCREMENT,
  `name` varchar(250) NOT NULL,
  `address` varchar(250) NOT NULL,
  `faculty_id` int(11) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

--
-- Dumping data for table `student`
--

INSERT INTO `student` (`name`, `address`, `faculty_id`) VALUES
('Name 1', 'Address 1', 1),
('Name 2', 'Address 2', 1),
('Name 3', 'Address 3', 2),
('Name 4', 'Address 4', 2),
('Name 5', 'Address 5', 2);

Structure of Faculty Table

Data of Faculty Table

Structure of Student Table

Data of Student Table

Create Entities

Create new folder named src. In src folder, create new folder named entities. In this folder, create new entities as below:

Faculty Entity

In entities folder, create new go file named faculty.entity.go as below:

package entities

import "fmt"

type Faculty struct {
	Id       int `gorm:"primary_key, AUTO_INCREMENT"`
	Name     string
	Students []Student `gorm:"ForeignKey:FacultyID"`
}

func (faculty *Faculty) TableName() string {
	return "faculty"
}

func (faculty Faculty) ToString() string {
	return fmt.Sprintf("id: %d\nname: %s", faculty.Id, faculty.Name)
}

Student Entity

In entities folder, create new go file named student.entity.go as below:

package entities

import "fmt"

type Student struct {
	Id        int `gorm:"primary_key, AUTO_INCREMENT"`
	Name      string
	Address   string
	FacultyID int `gorm:"column:faculty_id"`
	Faculty   Faculty
}

func (student *Student) TableName() string {
	return "student"
}

func (student Student) ToString() string {
	return fmt.Sprintf("id: %d\nname: %s\naddress: %s", student.Id, student.Name, student.Address)
}

Create Config

In src folder, create new folder named config. In this folder, create new file named config.go, this file is used to connect mysql database:

package config

import (
	"github.com/jinzhu/gorm"
	_ "github.com/jinzhu/gorm/dialects/mysql"
)

func GetDB() (*gorm.DB, error) {
	dbDriver := "mysql"
	dbName := "learngorm"
	dbUser := "root"
	dbPassword := "123456"
	db, err := gorm.Open(dbDriver, dbUser+":"+dbPassword+"@/"+dbName+"?charset=utf8&parseTime=True")
	if err != nil {
		return nil, err
	}
	return db, nil
}

Create Model

In src folder, create new folder named models. In models folder, create new file named faculty.model.go. This file contains methods to interact with the database.

package models

import (
	"config"
	"entities"
)

type FacultyModel struct {
}

func (facultyModel FacultyModel) FindAll() ([]entities.Faculty, error) {
	db, err := config.GetDB()
	if err != nil {
		return nil, err
	} else {
		var faculties []entities.Faculty
		db.Preload("Students").Find(&faculties)
		return faculties, nil
	}
}

Structure of Project

Run Application

In src folder, create new file named main.go as below and use go run main.go command to run program:

package main

import (
	"fmt"
	"models"
)

func main() {
	var facultyModel models.FacultyModel
	faculties, _ := facultyModel.FindAll()
	for _, faculty := range faculties {
		fmt.Println(faculty.ToString())
		fmt.Println("Students: ", len(faculty.Students))
		if len(faculty.Students) > 0 {
			for _, student := range faculty.Students {
				fmt.Println(student.ToString())
				fmt.Println("=============================")
			}
		}
		fmt.Println("--------------------")
	}
}

Output

id: 1
name: Faculty 1
Students:  2
id: 1
name: Name 1
address: Address 1
=============================
id: 2
name: Name 2
address: Address 2
=============================
--------------------
id: 2
name: Faculty 2
Students:  3
id: 3
name: Name 3
address: Address 3
=============================
id: 4
name: Name 4
address: Address 4
=============================
id: 5
name: Name 5
address: Address 5
=============================
--------------------
id: 3
name: Faculty 3
Students:  0
--------------------