初始化Go学习项目

go-gorm-demo/relation_many_to_many.go

@@ -0,0 +1,96 @@
+package main
+
+import (
+	"fmt"
+
+	"gorm.io/driver/sqlite"
+	"gorm.io/gorm"
+)
+
+// 学生和课程：多对多关系
+type Student struct {
+	ID      uint     `gorm:"primaryKey"`
+	Name    string   `gorm:"size:100"`
+	Courses []Course `gorm:"many2many:student_courses;"` // 多对多
+}
+
+type Course struct {
+	ID       uint      `gorm:"primaryKey"`
+	Name     string    `gorm:"size:100"`
+	Students []Student `gorm:"many2many:student_courses;"` // 多对多
+}
+
+func main() {
+	db, _ := gorm.Open(sqlite.Open("test.db"), &gorm.Config{})
+	//db.AutoMigrate(&Student{}, &Course{})
+
+	// 1. 创建课程
+	//math := Course{Name: "Math"}
+	//physics := Course{Name: "Physics"}
+	//chemistry := Course{Name: "Chemistry"}
+	//db.Create(&math)
+	//db.Create(&physics)
+	//db.Create(&chemistry)
+
+	// 2. 创建学生并关联课程
+	//alice := Student{
+	//	Name:    "Alice",
+	//	Courses: []Course{math, physics},
+	//}
+	//bob := Student{
+	//	Name:    "Bob",
+	//	Courses: []Course{physics, chemistry},
+	//}
+	//db.Create(&alice)
+	//db.Create(&bob)
+	//fmt.Println("Students and courses created")
+
+	//查询数据库的alice的学生
+	var alice Student
+	db.Where("name = ?", "Alice").First(&alice)
+
+	//查询数据库的Bob学生
+	var bob Student
+	db.Where("name = ?", "Bob").First(&bob)
+
+	//查询课程
+	var math Course
+	db.Where("name = ?", "Math").First(&math)
+
+	//// 5. 添加关联
+	//db.Model(&alice).Association("Courses").Append(&chemistry)
+	//fmt.Println("Alice enrolled in Chemistry")
+
+	//// 7. 替换所有关联
+	//db.Model(&alice).Association("Courses").Replace(&math)
+	//fmt.Println("Alice now only takes Math")
+
+	// 8. 清空关联
+	db.Model(&bob).Association("Courses").Clear()
+	fmt.Println("Bob dropped all courses")
+
+	// 3. 查询学生的课程
+	var student1 Student
+	db.Preload("Courses").First(&student1, 1)
+	fmt.Printf("%s's courses:\n", student1.Name)
+	for _, course := range student1.Courses {
+		fmt.Printf("  - %s\n", course.Name)
+	}
+
+	// 4. 查询课程的学生
+	var course1 Course
+	db.Preload("Students").First(&course1, 1)
+	fmt.Printf("%s course students:\n", course1.Name)
+	for _, student := range course1.Students {
+		fmt.Printf("  - %s\n", student.Name)
+	}
+
+	//查询bob的课程
+	var student2 Student
+	db.Preload("Courses").First(&student2, 2)
+	fmt.Printf("%s's courses:\n", student2.Name)
+	for _, course := range student2.Courses {
+		fmt.Printf("  - %s\n", course.Name)
+	}
+
+}