[TOC] ## code ``` type User struct { gorm.Model Username string Orders []Order } type Order struct { gorm.Model UserID uint Price float64 } // 查找 user 时预加载相关 users 的Order字段 db.Preload("Orders").Find(&users) // SELECT * FROM users; // SELECT * FROM orders WHERE user_id IN (1,2,3,4); db.Preload("Orders").Preload("Profile").Preload("Role").Find(&users) // SELECT * FROM users; // SELECT * FROM orders WHERE user_id IN (1,2,3,4); // has many // SELECT * FROM profiles WHERE user_id IN (1,2,3,4); // has one // SELECT * FROM roles WHERE id IN (4,5,6); // belongs to ``` 子结构体若为非引用类型,则在为空时候插入为报子表插入失败,可修改为 ``` type User struct { gorm.Model Username string Orders []*Order } db.Create(users) ```