Example: golang gorm postgres uuid relation

example output

[2018-08-15 16:35:42]  [7.58ms]  CREATE TABLE "parents" ("id" uuid DEFAULT uuid_generate_v4(),"name" text , PRIMARY KEY ("id"))
[0 rows affected or returned ]

[2018-08-15 16:35:42]  [7.22ms]  CREATE TABLE "children" ("id" uuid DEFAULT uuid_generate_v4(),"parent_id" uuid REFERENCES parents(id),"name" text , PRIMARY KEY ("id"))
[0 rows affected or returned ]

[2018-08-15 16:35:42]  [2.54ms]  INSERT INTO "parents" ("name") VALUES ('I am the parent') RETURNING "parents"."id"
[1 rows affected or returned ]

[2018-08-15 16:35:42]  [4.31ms]  SELECT "id" FROM "parents"  WHERE (id = 'fd763ae6-b0e1-4808-bac6-73119eca075b')
[1 rows affected or returned ]

[2018-08-15 16:35:42]  [5.19ms]  INSERT INTO "children" ("parent_id","name") VALUES ('fd763ae6-b0e1-4808-bac6-73119eca075b','I am the child') RETURNING "children"."id"
[1 rows affected or returned ]

[2018-08-15 16:35:42]  [1.78ms]  SELECT "id" FROM "children"  WHERE (id = '8c1424a8-62db-4b71-a136-8825a7d2f44f')
[1 rows affected or returned ]
{8c1424a8-62db-4b71-a136-8825a7d2f44f fd763ae6-b0e1-4808-bac6-73119eca075b {fd763ae6-b0e1-4808-bac6-73119eca075b I am the parent} I am the child}

[2018-08-15 16:35:42]  [1.67ms]  SELECT * FROM "children"  WHERE (id = '8c1424a8-62db-4b71-a136-8825a7d2f44f')
[1 rows affected or returned ]

[2018-08-15 16:35:42]  [1.80ms]  SELECT * FROM "parents"  WHERE ("id" IN ('fd763ae6-b0e1-4808-bac6-73119eca075b'))
[1 rows affected or returned ]
(main.Child) {
 ID: (uuid.UUID) (len=16 cap=16) 8c1424a8-62db-4b71-a136-8825a7d2f44f,
 ParentID: (uuid.UUID) (len=16 cap=16) fd763ae6-b0e1-4808-bac6-73119eca075b,
 Parent: (main.Parent) {
  ID: (uuid.UUID) (len=16 cap=16) fd763ae6-b0e1-4808-bac6-73119eca075b,
  Name: (string) (len=15) "I am the parent"
 },
 Name: (string) (len=14) "I am the child"
}

Example: golang gorm postgres uuid relation.md

Example: golang gorm postgres uuid relation

I was trying forever to get autoloading relationships working with postgres 9.4 and gorm and primary keys of type uuid.

Many tutorials and examples, even those on the official docs were just not workiong or missing important details.

The program in this gist creates the table structure and inserts a nested record. A parent and a child object is created by simply creating the child, which holds the relation to a parent. The child element then is queried by ID. The returned object holds the nested parent object.

Used package versions:

• github.com/jinzhu/gorm v1.9.1 6ed508ec6a4ecb3531899a69cbc746ccf65a4166
• github.com/satori/go.uuid v1.2.0 f58768cc1a7a7e77a3bd49e98cdd21419399b6a3

main.go

package main

import (
	"fmt"
	"os"

	"github.com/davecgh/go-spew/spew"
	"github.com/jinzhu/gorm"
	_ "github.com/jinzhu/gorm/dialects/postgres"
	"github.com/satori/go.uuid"
)

type Parent struct { // table name: parents
	ID   uuid.UUID `gorm:"primary_key;type:uuid;default:uuid_generate_v4()"`
	Name string
}

type Child struct { // table name: children
	ID       uuid.UUID `gorm:"primary_key;type:uuid;default:uuid_generate_v4()"`
	ParentID uuid.UUID `gorm:"type:uuid REFERENCES parents(id)"`
	Parent   Parent    `gorm:"ForeignKey:ParentID;AssociationForeignKey:ID`
	Name     string
}

func main() {

	dbString := "postgres://user:password@localhost/schema?sslmode=disable"

	db, err := gorm.Open("postgres", dbString)
	if err != nil {
		fmt.Fprintf(os.Stderr, "db connection failed: %s", err.Error())
		os.Exit(1)
	}

	db.LogMode(true)
	defer db.Close()

	//dropTables(db)
	createTables(db)
	newID := createNewRecord(db)
	showRecord(db, newID)
}

func dropTables(db *gorm.DB) {
	db.DropTable(&Child{})
	db.DropTable(&Parent{})
}

func createTables(db *gorm.DB) {
	db.CreateTable(&Parent{})
	db.CreateTable(&Child{})
}

func createNewRecord(db *gorm.DB) uuid.UUID {
	testObject := Child{
		Name: "I am the child",
		Parent: Parent{
			Name: "I am the parent",
		},
	}
	db.Create(&testObject)
	return testObject.ID, 
}

func showRecord(db *gorm.DB, key interface{}) {
	var child Child
	db.Set("gorm:auto_preload", true).Find(&child, "id = ?", key)
	spew.Dump(child)
}

@gipsh Thank you so much! Save my day!