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example_many2many_test.go
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example_many2many_test.go
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package pg_test
import (
"fmt"
"github.com/go-pg/pg"
"github.com/go-pg/pg/orm"
)
func init() {
// Register many to many model so ORM can better recognize m2m relation.
// This should be done before dependant models are used.
orm.Tables.Register((*ItemToItem)(nil))
}
type Item struct {
Id int
Items []Item `pg:"many2many:item_to_items,joinFK:sub_id"`
}
type ItemToItem struct {
ItemId int
SubId int
}
func createManyToManyTables(db *pg.DB) error {
models := []interface{}{
(*Item)(nil),
(*ItemToItem)(nil),
}
for _, model := range models {
err := db.CreateTable(model, &orm.CreateTableOptions{
Temp: true,
})
if err != nil {
return err
}
}
return nil
}
func ExampleDB_Model_manyToMany() {
db := connect()
defer db.Close()
if err := createManyToManyTables(db); err != nil {
panic(err)
}
values := []interface{}{
&Item{Id: 1},
&Item{Id: 2},
&Item{Id: 3},
&ItemToItem{ItemId: 1, SubId: 2},
&ItemToItem{ItemId: 1, SubId: 3},
}
for _, v := range values {
err := db.Insert(v)
if err != nil {
panic(err)
}
}
// Select item and all subitems with following queries:
//
// SELECT "item".* FROM "items" AS "item" ORDER BY "item"."id" LIMIT 1
//
// SELECT * FROM "items" AS "item"
// JOIN "item_to_items" ON ("item_to_items"."item_id") IN ((1))
// WHERE ("item"."id" = "item_to_items"."sub_id")
var item Item
err := db.Model(&item).Column("item.*").Relation("Items").First()
if err != nil {
panic(err)
}
fmt.Println("Item", item.Id)
fmt.Println("Subitems", item.Items[0].Id, item.Items[1].Id)
// Output: Item 1
// Subitems 2 3
}