1. 查询

1. 查询

1.1. 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;
// 获取一条记录，不指定排序
db.Take(&user)
//// SELECT * FROM users 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;
// 获取所有的记录
db.Find(&users)
//// SELECT * FROM users;
// 通过主键进行查询 (仅适用于主键是数字类型)
db.First(&user, 10)
//// SELECT * FROM users WHERE id = 10;

1.1.1. Where

原生 SQL

// 获取第一条匹配的记录
db.Where("name = ?", "jinzhu").First(&user)
//// SELECT * FROM users WHERE name = 'jinzhu' limit 1;
// 获取所有匹配的记录
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)
// BETWEEN
db.Where("created_at BETWEEN ? AND ?", lastWeek, today).Find(&users)

Struct & Map

// 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;
// 多主键 slice 查询
db.Where([]int64{20, 21, 22}).Find(&users)
//// SELECT * FROM users WHERE id IN (20, 21, 22);

NOTE 当通过struct进行查询的时候，GORM 将会查询这些字段的非零值，意味着你的字段包含 0， ''， false 或者其他零值, 将不会出现在查询语句中，例如:

db.Where(&User{Name: "jinzhu", Age: 0}).Find(&users)
//// SELECT * FROM users WHERE name = "jinzhu";

你可以考虑适用指针类型或者 scanner/valuer 来避免这种情况。

// 使用指针类型
type User struct {
  gorm.Model
  Name string
  Age  *int
}
// 使用 scanner/valuer
type User struct {
  gorm.Model
  Name string
  Age  sql.NullInt64
}

1.1.2. Not

和 Where查询类似

db.Not("name", "jinzhu").First(&user)
//// SELECT * FROM users WHERE name <> "jinzhu" LIMIT 1;
// 不包含
db.Not("name", []string{"jinzhu", "jinzhu 2"}).Find(&users)
//// SELECT * FROM users WHERE name NOT IN ("jinzhu", "jinzhu 2");
//不在主键 slice 中
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;
// 原生 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";

1.1.3. Or

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)
//// SELECT * FROM users WHERE name = 'jinzhu' OR name = 'jinzhu 2';

1.1.4. 行内条件查询

和 Where 查询类似。

需要注意的是，当使用链式调用传入行内条件查询时，这些查询不会被传参给后续的中间方法。

// 通过主键进行查询 (仅适用于主键是数字类型)
db.First(&user, 23)
//// SELECT * FROM users WHERE id = 23 LIMIT 1;
// 非数字类型的主键查询
db.First(&user, "id = ?", "string_primary_key")
//// SELECT * FROM users WHERE id = 'string_primary_key' LIMIT 1;
// 原生 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;

1.1.5. 额外的查询选项

// 为查询 SQL 添加额外的选项
db.Set("gorm:query_option", "FOR UPDATE").First(&user, 10)
//// SELECT * FROM users WHERE id = 10 FOR UPDATE;

1.2. FirstOrInit

获取第一条匹配的记录，或者通过给定的条件下初始一条新的记录（仅适用与于 struct 和 map 条件）。

// 未查询到
db.FirstOrInit(&user, User{Name: "non_existing"})
//// user -> User{Name: "non_existing"}
// 查询到
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}

1.2.1. Attrs

如果未找到记录，则使用参数初始化 struct

// 未查询到
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}
// 查询到
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}

1.2.2. Assign

无论是否查询到数据，都将参数赋值给 struct

// 未查询到
db.Where(User{Name: "non_existing"}).Assign(User{Age: 20}).FirstOrInit(&user)
//// user -> User{Name: "non_existing", Age: 20}
// 查询到
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}

1.3. FirstOrCreate

获取第一条匹配的记录，或者通过给定的条件创建一条记录（仅适用与于 struct 和 map 条件）。

// 未查询到
db.FirstOrCreate(&user, User{Name: "non_existing"})
//// INSERT INTO "users" (name) VALUES ("non_existing");
//// user -> User{Id: 112, Name: "non_existing"}
// 查询到
db.Where(User{Name: "Jinzhu"}).FirstOrCreate(&user)
//// user -> User{Id: 111, Name: "Jinzhu"}

1.3.1. Attrs

如果未查询到记录，通过给定的参数赋值给 struct ，然后使用这些值添加一条记录。

// 未查询到
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}
// 查询到
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}

1.3.2. Assign

无论是否查询到，都将其分配给记录，并保存到数据库中。

// 未查询到
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}
// 查询到
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}

1.4. 高级查询

1.4.1. 子查询

使用 *gorm.expr 进行子查询

db.Where("amount > ?", DB.Table("orders").Select("AVG(amount)").Where("state = ?", "paid").QueryExpr()).Find(&orders)
// SELECT * FROM "orders"  WHERE "orders"."deleted_at" IS NULL AND (amount > (SELECT AVG(amount) FROM "orders"  WHERE (state = 'paid')));

1.4.2. 查询

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;

1.4.3. Order

使用 Order 从数据库查询记录时，当第二个参数设置为 true 时，将会覆盖之前的定义条件。

db.Order("age desc, name").Find(&users)
//// SELECT * FROM users ORDER BY age desc, name;
// 多个排序条件
db.Order("age desc").Order("name").Find(&users)
//// SELECT * FROM users ORDER BY age desc, name;
// 重新排序
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)

1.4.4. Limit

指定要查询的最大记录数

db.Limit(3).Find(&users)
//// SELECT * FROM users LIMIT 3;
// 用 -1 取消 LIMIT 限制条件
db.Limit(10).Find(&users1).Limit(-1).Find(&users2)
//// SELECT * FROM users LIMIT 10; (users1)
//// SELECT * FROM users; (users2)

1.4.5. 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;
// 用 -1 取消 OFFSET 限制条件
db.Offset(10).Find(&users1).Offset(-1).Find(&users2)
//// SELECT * FROM users OFFSET 10; (users1)
//// SELECT * FROM users; (users2)

1.4.6. Count

获取模型记录数

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;

注意：在查询链中使用 Count 时，必须放在最后一个位置，因为它会覆盖 SELECT 查询条件。

1.4.7. Group 和 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)

1.4.8. Joins

指定关联条件

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)
// 多个关联查询
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)

1.5. Pluck

使用 Pluck 从模型中查询单个列作为集合。如果想查询多个列，应该使用 Scan 代替。

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)
// Requesting more than one column? Do it like this:
db.Select("name, age").Find(&users)

1.6. Scan

将 Scan 查询结果放入另一个结构体中。

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)