## 查询 ~~~ // 获取第一条记录,按主键排序 db.First(&user) //// SELECT * FROM users ORDER BY id LIMIT 1; // 获取最后一条记录,按主键排序 db.Last(&user) //// SELECT * FROM users ORDER BY id DESC LIMIT 1; // 获取所有记录 db.Find(&users) //// SELECT * FROM users; // 使用主键获取记录 db.First(&user, 10) //// SELECT * FROM users WHERE id = 10; ~~~ ### 1. Where查询条件 (简单SQL) ~~~ // 获取第一个匹配记录 db.Where("name = ?", "jinzhu").First(&user) //// SELECT * FROM users WHERE name = 'jinzhu' limit 1; // 获取所有匹配记录 db.Where("name = ?", "jinzhu").Find(&users) //// SELECT * FROM users WHERE name = 'jinzhu'; db.Where("name <> ?", "jinzhu").Find(&users) // IN db.Where("name in (?)", []string{"jinzhu", "jinzhu 2"}).Find(&users) // LIKE db.Where("name LIKE ?", "%jin%").Find(&users) // AND db.Where("name = ? AND age >= ?", "jinzhu", "22").Find(&users) // Time db.Where("updated_at > ?", lastWeek).Find(&users) db.Where("created_at BETWEEN ? AND ?", lastWeek, today).Find(&users) ~~~ ### 2. Where查询条件 (Struct & Map) 注意:当使用struct查询时,GORM将只查询那些具有值的字段 ~~~ // Struct db.Where(&User{Name: "jinzhu", Age: 20}).First(&user) //// SELECT * FROM users WHERE name = "jinzhu" AND age = 20 LIMIT 1; // Map db.Where(map[string]interface{}{"name": "jinzhu", "age": 20}).Find(&users) //// SELECT * FROM users WHERE name = "jinzhu" AND age = 20; // 主键的Slice db.Where([]int64{20, 21, 22}).Find(&users) //// SELECT * FROM users WHERE id IN (20, 21, 22); ~~~ ### 3. Not条件查询 ~~~ db.Not("name", "jinzhu").First(&user) //// SELECT * FROM users WHERE name <> "jinzhu" LIMIT 1; // Not In db.Not("name", []string{"jinzhu", "jinzhu 2"}).Find(&users) //// SELECT * FROM users WHERE name NOT IN ("jinzhu", "jinzhu 2"); // Not In slice of primary keys db.Not([]int64{1,2,3}).First(&user) //// SELECT * FROM users WHERE id NOT IN (1,2,3); db.Not([]int64{}).First(&user) //// SELECT * FROM users; // Plain SQL db.Not("name = ?", "jinzhu").First(&user) //// SELECT * FROM users WHERE NOT(name = "jinzhu"); // Struct db.Not(User{Name: "jinzhu"}).First(&user) //// SELECT * FROM users WHERE name <> "jinzhu"; ~~~ ### 4. 带内联条件的查询 注意:使用主键查询时,应仔细检查所传递的值是否为有效主键,以避免SQL注入 ~~~ // 按主键获取 db.First(&user, 23) //// SELECT * FROM users WHERE id = 23 LIMIT 1; // 简单SQL db.Find(&user, "name = ?", "jinzhu") //// SELECT * FROM users WHERE name = "jinzhu"; db.Find(&users, "name <> ? AND age > ?", "jinzhu", 20) //// SELECT * FROM users WHERE name <> "jinzhu" AND age > 20; // Struct db.Find(&users, User{Age: 20}) //// SELECT * FROM users WHERE age = 20; // Map db.Find(&users, map[string]interface{}{"age": 20}) //// SELECT * FROM users WHERE age = 20; ~~~ ### 5. Or条件查询 ~~~ db.Where("role = ?", "admin").Or("role = ?", "super_admin").Find(&users) //// SELECT * FROM users WHERE role = 'admin' OR role = 'super_admin'; // Struct db.Where("name = 'jinzhu'").Or(User{Name: "jinzhu 2"}).Find(&users) //// SELECT * FROM users WHERE name = 'jinzhu' OR name = 'jinzhu 2'; // Map db.Where("name = 'jinzhu'").Or(map[string]interface{}{"name": "jinzhu 2"}).Find(&users) ~~~ ### 6. 查询链 Gorm有一个可链接的API,你可以这样使用它 ~~~ db.Where("name <> ?","jinzhu").Where("age >= ? and role <> ?",20,"admin").Find(&users) //// SELECT * FROM users WHERE name <> 'jinzhu' AND age >= 20 AND role <> 'admin'; db.Where("role = ?", "admin").Or("role = ?", "super_admin").Not("name = ?", "jinzhu").Find(&users) ~~~ ### 7. 扩展查询选项 ~~~ // 为Select语句添加扩展SQL选项 db.Set("gorm:query_option", "FOR UPDATE").First(&user, 10) //// SELECT * FROM users WHERE id = 10 FOR UPDATE; ~~~ ### 8. FirstOrInit 获取第一个匹配的记录,或者使用给定的条件初始化一个新的记录(仅适用于struct,map条件) ~~~ // Unfound db.FirstOrInit(&user, User{Name: "non_existing"}) //// user -> User{Name: "non_existing"} // Found db.Where(User{Name: "Jinzhu"}).FirstOrInit(&user) //// user -> User{Id: 111, Name: "Jinzhu", Age: 20} db.FirstOrInit(&user, map[string]interface{}{"name": "jinzhu"}) //// user -> User{Id: 111, Name: "Jinzhu", Age: 20} ~~~ ### 9. Attrs 如果未找到记录,则使用参数初始化结构 ~~~ // Unfound db.Where(User{Name: "non_existing"}).Attrs(User{Age: 20}).FirstOrInit(&user) //// SELECT * FROM USERS WHERE name = 'non_existing'; //// user -> User{Name: "non_existing", Age: 20} db.Where(User{Name: "non_existing"}).Attrs("age", 20).FirstOrInit(&user) //// SELECT * FROM USERS WHERE name = 'non_existing'; //// user -> User{Name: "non_existing", Age: 20} // Found db.Where(User{Name: "Jinzhu"}).Attrs(User{Age: 30}).FirstOrInit(&user) //// SELECT * FROM USERS WHERE name = jinzhu'; //// user -> User{Id: 111, Name: "Jinzhu", Age: 20} ~~~ ### 10. Assign 将参数分配给结果,不管它是否被找到 ~~~ // Unfound db.Where(User{Name: "non_existing"}).Assign(User{Age: 20}).FirstOrInit(&user) //// user -> User{Name: "non_existing", Age: 20} // Found db.Where(User{Name: "Jinzhu"}).Assign(User{Age: 30}).FirstOrInit(&user) //// SELECT * FROM USERS WHERE name = jinzhu'; //// user -> User{Id: 111, Name: "Jinzhu", Age: 30} ~~~ ### 11. FirstOrCreate 获取第一个匹配的记录,或创建一个具有给定条件的新记录(仅适用于struct, map条件) ~~~ // Unfound db.FirstOrCreate(&user, User{Name: "non_existing"}) //// INSERT INTO "users" (name) VALUES ("non_existing"); //// user -> User{Id: 112, Name: "non_existing"} // Found db.Where(User{Name: "Jinzhu"}).FirstOrCreate(&user) //// user -> User{Id: 111, Name: "Jinzhu"} ~~~ ### 12. Attrs 如果未找到记录,则为参数分配结构 ~~~ // Unfound db.Where(User{Name: "non_existing"}).Attrs(User{Age: 20}).FirstOrCreate(&user) //// SELECT * FROM users WHERE name = 'non_existing'; //// INSERT INTO "users" (name, age) VALUES ("non_existing", 20); //// user -> User{Id: 112, Name: "non_existing", Age: 20} // Found db.Where(User{Name: "jinzhu"}).Attrs(User{Age: 30}).FirstOrCreate(&user) //// SELECT * FROM users WHERE name = 'jinzhu'; //// user -> User{Id: 111, Name: "jinzhu", Age: 20} ~~~ ### 13. Assign 将其分配给记录,而不管它是否被找到,并保存回数据库。 ~~~ // Unfound db.Where(User{Name: "non_existing"}).Assign(User{Age: 20}).FirstOrCreate(&user) //// SELECT * FROM users WHERE name = 'non_existing'; //// INSERT INTO "users" (name, age) VALUES ("non_existing", 20); //// user -> User{Id: 112, Name: "non_existing", Age: 20} // Found db.Where(User{Name: "jinzhu"}).Assign(User{Age: 30}).FirstOrCreate(&user) //// SELECT * FROM users WHERE name = 'jinzhu'; //// UPDATE users SET age=30 WHERE id = 111; //// user -> User{Id: 111, Name: "jinzhu", Age: 30} ~~~ ### 14. Select 指定要从数据库检索的字段,默认情况下,将选择所有字段; ~~~ db.Select("name, age").Find(&users) //// SELECT name, age FROM users; db.Select([]string{"name", "age"}).Find(&users) //// SELECT name, age FROM users; db.Table("users").Select("COALESCE(age,?)", 42).Rows() //// SELECT COALESCE(age,'42') FROM users; ~~~ ### 15. Order 在从数据库检索记录时指定顺序,将重排序设置为`true`以覆盖定义的条件 ~~~ db.Order("age desc, name").Find(&users) //// SELECT * FROM users ORDER BY age desc, name; // Multiple orders db.Order("age desc").Order("name").Find(&users) //// SELECT * FROM users ORDER BY age desc, name; // ReOrder db.Order("age desc").Find(&users1).Order("age", true).Find(&users2) //// SELECT * FROM users ORDER BY age desc; (users1) //// SELECT * FROM users ORDER BY age; (users2) ~~~ ### 16. Limit 指定要检索的记录数 ~~~ db.Limit(3).Find(&users) //// SELECT * FROM users LIMIT 3; // Cancel limit condition with -1 db.Limit(10).Find(&users1).Limit(-1).Find(&users2) //// SELECT * FROM users LIMIT 10; (users1) //// SELECT * FROM users; (users2) ~~~ ### 17. Offset 指定在开始返回记录之前要跳过的记录数 ~~~ db.Offset(3).Find(&users) //// SELECT * FROM users OFFSET 3; // Cancel offset condition with -1 db.Offset(10).Find(&users1).Offset(-1).Find(&users2) //// SELECT * FROM users OFFSET 10; (users1) //// SELECT * FROM users; (users2) ~~~ ### 18. Count 获取模型的记录数 ~~~ db.Where("name = ?", "jinzhu").Or("name = ?", "jinzhu 2").Find(&users).Count(&count) //// SELECT * from USERS WHERE name = 'jinzhu' OR name = 'jinzhu 2'; (users) //// SELECT count(*) FROM users WHERE name = 'jinzhu' OR name = 'jinzhu 2'; (count) db.Model(&User{}).Where("name = ?", "jinzhu").Count(&count) //// SELECT count(*) FROM users WHERE name = 'jinzhu'; (count) db.Table("deleted_users").Count(&count) //// SELECT count(*) FROM deleted_users; ~~~ ### 19. Group & Having ~~~ rows, err := db.Table("orders").Select("date(created_at) as date, sum(amount) as total").Group("date(created_at)").Rows() for rows.Next() { ... } rows, err := db.Table("orders").Select("date(created_at) as date, sum(amount) as total").Group("date(created_at)").Having("sum(amount) > ?", 100).Rows() for rows.Next() { ... } type Result struct { Date time.Time Total int64 } db.Table("orders").Select("date(created_at) as date, sum(amount) as total").Group("date(created_at)").Having("sum(amount) > ?", 100).Scan(&results) ~~~ ### 20. Join 指定连接条件 ~~~ rows, err := db.Table("users").Select("users.name, emails.email").Joins("left join emails on emails.user_id = users.id").Rows() for rows.Next() { ... } db.Table("users").Select("users.name, emails.email").Joins("left join emails on emails.user_id = users.id").Scan(&results) // 多个连接与参数 db.Joins("JOIN emails ON emails.user_id = users.id AND emails.email = ?", "jinzhu@example.org").Joins("JOIN credit_cards ON credit_cards.user_id = users.id").Where("credit_cards.number = ?", "411111111111").Find(&user) ~~~ ### 21. Pluck 将模型中的单个列作为地图查询,如果要查询多个列,可以使用Scan ~~~ var ages []int64 db.Find(&users).Pluck("age", &ages) var names []string db.Model(&User{}).Pluck("name", &names) db.Table("deleted_users").Pluck("name", &names) // 要返回多个列,做这样: db.Select("name, age").Find(&users) ~~~ ### 22. Scan 将结果扫描到另一个结构中。 ~~~ type Result struct { Name string Age int } var result Result db.Table("users").Select("name, age").Where("name = ?", 3).Scan(&result) // Raw SQL db.Raw("SELECT name, age FROM users WHERE name = ?", 3).Scan(&result) ~~~ ### 23. Scopes 将当前数据库连接传递到`func(*DB) *DB`,可以用于动态添加条件 ~~~ func AmountGreaterThan1000(db *gorm.DB) *gorm.DB { return db.Where("amount > ?", 1000) } func PaidWithCreditCard(db *gorm.DB) *gorm.DB { return db.Where("pay_mode_sign = ?", "C") } func PaidWithCod(db *gorm.DB) *gorm.DB { return db.Where("pay_mode_sign = ?", "C") } func OrderStatus(status []string) func (db *gorm.DB) *gorm.DB { return func (db *gorm.DB) *gorm.DB { return db.Scopes(AmountGreaterThan1000).Where("status in (?)", status) } } db.Scopes(AmountGreaterThan1000, PaidWithCreditCard).Find(&orders) // 查找所有信用卡订单和金额大于1000 db.Scopes(AmountGreaterThan1000, PaidWithCod).Find(&orders) // 查找所有COD订单和金额大于1000 db.Scopes(OrderStatus([]string{"paid", "shipped"})).Find(&orders) // 查找所有付费,发货订单 ~~~ ### 24. 指定表名 ~~~ // 使用User结构定义创建`deleted_users`表 db.Table("deleted_users").CreateTable(&User{}) var deleted_users []User db.Table("deleted_users").Find(&deleted_users) //// SELECT * FROM deleted_users; db.Table("deleted_users").Where("name = ?", "jinzhu").Delete() //// DELETE FROM deleted_users WHERE name = 'jinzhu'; ~~~