add tutorial 4

Makefile

@@ -5,4 +5,7 @@ tutorial_2:
 	go run -tags=tutorial_2 .
 
 tutorial_3:
-	go run -tags=tutorial_3 .
+	go run -tags=tutorial_3 .
+
+tutorial_4:
+	go run -tags=tutorial_4 .

tutorial_4.go

@@ -0,0 +1,57 @@
+//go:build tutorial_4
+// +build tutorial_4
+
+package main
+
+import (
+	"fmt"
+	"log"
+
+	"github.com/ditrit/badaas-orm-tutorial/conditions"
+	"github.com/ditrit/badaas-orm-tutorial/models"
+	"github.com/ditrit/badaas/orm"
+	"github.com/ditrit/badaas/orm/model"
+	"go.uber.org/fx"
+)
+
+// Target: get all cities whose name is 'Paris' and preload its country
+func tutorial(crudCityService orm.CRUDService[models.City, model.UUID], shutdowner fx.Shutdowner) {
+	cities, err := crudCityService.Query(
+		conditions.CityName(orm.Eq("Paris")),
+		conditions.CityPreloadCountry,
+	)
+
+	// Equivalent to:
+	// cities, err := crudCityService.Query(
+	// 	conditions.CityName(orm.Eq("Paris")),
+	// 	conditions.CityCountry(
+	// 		conditions.CountryPreloadAttributes,
+	// 	),
+	// )
+
+	// SQL executed:
+	// SELECT cities.*,
+	//    Country.id AS Country__id,Country.created_at AS Country__created_at,Country.updated_at AS Country__updated_at,Country.deleted_at AS Country__deleted_at,Country.name AS Country__name,Country.capital_id AS Country__capital_id
+	// FROM cities
+	// LEFT JOIN countries Country ON
+	//    Country.id = cities.country_id AND Country.deleted_at IS NULL
+	// WHERE cities.name = "Paris" AND cities.deleted_at IS NULL
+
+	if err != nil {
+		log.Panicln(err)
+	}
+
+	log.Println("Cities named 'Paris' are:")
+	for i, city := range cities {
+		fmt.Printf("\t%v: %+v with country: ", i+1, city)
+
+		cityCountry, err := city.GetCountry()
+		if err != nil {
+			log.Panicln(err)
+		}
+
+		fmt.Printf("%+v\n", cityCountry)
+	}
+
+	shutdowner.Shutdown()
+}