Multiple One to Many Relations in GORM - mysql

Question

I have a struct definition in GO like this
package models
//StoryStatus indicates the current state of the story
type StoryStatus string
const (
//Progress indicates a story is currenty being written
Progress StoryStatus = "progress"
//Completed indicates a story was completed
Completed StoryStatus = "completed"
)
//Story holds detials of story
type Story struct {
ID int
Title string `gorm:"type:varchar(100);unique_index"`
Status StoryStatus `sql:"type ENUM('progress', 'completed');default:'progress'"`
Paragraphs []Paragraph `gorm:"ForeignKey:StoryID"`
}
//Paragraph is linked to a story
//A story can have around configurable paragraph
type Paragraph struct {
ID int
StoryID int
Sentences []Sentence `gorm:"ForeignKey:ParagraphID"`
}
//Sentence are linked to paragraph
//A paragraph can have around configurable paragraphs
type Sentence struct {
ID uint
Value string
Status bool
ParagraphID uint
}
I am using GORM for orm in GO.
How do I fetch all the information for a story based on story id like all the paragraphs and all the sentences for each paragraph.
The GORM example show only with 2 models to use preload

Answer 1

This is what you're looking for:
db, err := gorm.Open("mysql", "user:password#/dbname?charset=utf8&parseTime=True&loc=Local")
defer db.Close()
story := &Story{}
db.Preload("Paragraphs").Preload("Paragraphs.Sentences").First(story, 1)
It finds the story with the id = 1 and preloads its relationships
fmt.Printf("%+v\n", story)
This prints out the result nicely for you
Side note:
You can turn on log mode of Gorm so that you can see the underlying queries, to debug, or any other purposes:
db.LogMode(true)

Answer 2

Looking this [example][1] this One to many.
package main
import (
"log"
"github.com/jinzhu/gorm"
_ "github.com/jinzhu/gorm/dialects/sqlite"
"github.com/kylelemons/godebug/pretty"
)
// Order
type Order struct {
gorm.Model
Status string
OrderItems []OrderItem
}
// Order line item
type OrderItem struct {
gorm.Model
OrderID uint
ItemID uint
Item Item
Quantity int
}
// Product
type Item struct {
gorm.Model
ItemName string
Amount float32
}
var (
items = []Item{
{ItemName: "Go Mug", Amount: 12.49},
{ItemName: "Go Keychain", Amount: 6.95},
{ItemName: "Go Tshirt", Amount: 17.99},
}
)
func main() {
db, err := gorm.Open("sqlite3", "/tmp/gorm.db")
db.LogMode(true)
if err != nil {
log.Panic(err)
}
defer db.Close()
// Migrate the schema
db.AutoMigrate(&OrderItem{}, &Order{}, &Item{})
// Create Items
for index := range items {
db.Create(&items[index])
}
order := Order{Status: "pending"}
db.Create(&order)
item1 := OrderItem{OrderID: order.ID, ItemID: items[0].ID, Quantity: 1}
item2 := OrderItem{OrderID: order.ID, ItemID: items[1].ID, Quantity: 4}
db.Create(&item1)
db.Create(&item2)
// Query with joins
rows, err := db.Table("orders").Where("orders.id = ? and status = ?", order.ID, "pending").
Joins("Join order_items on order_items.order_id = orders.id").
Joins("Join items on items.id = order_items.id").
Select("orders.id, orders.status, order_items.order_id, order_items.item_id, order_items.quantity" +
", items.item_name, items.amount").Rows()
if err != nil {
log.Panic(err)
}
defer rows.Close()
// Values to load into
newOrder := &Order{}
newOrder.OrderItems = make([]OrderItem, 0)
for rows.Next() {
orderItem := OrderItem{}
item := Item{}
err = rows.Scan(&newOrder.ID, &newOrder.Status, &orderItem.OrderID, &orderItem.ItemID, &orderItem.Quantity, &item.ItemName, &item.Amount)
if err != nil {
log.Panic(err)
}
orderItem.Item = item
newOrder.OrderItems = append(newOrder.OrderItems, orderItem)
}
log.Print(pretty.Sprint(newOrder))
}
[1]: https://stackoverflow.com/questions/35821810/golang-gorm-one-to-many-with-has-one