Gen Query

检索单个对象

GORM 提供了 First、Take、Last 方法，以便从数据库中检索单个对象。当查询数据库时它添加了 LIMIT 1 条件，且没有找到记录时，它会返回 ErrRecordNotFound 错误

u := query.User

// Get the first record ordered by primary key
user, err := u.WithContext(ctx).First()
// SELECT * FROM users ORDER BY id LIMIT 1;

// Get one record, no specified order
user, err := u.WithContext(ctx).Take()
// SELECT * FROM users LIMIT 1;

// Get last record, ordered by primary key desc
user, err := u.WithContext(ctx).Last()
// SELECT * FROM users ORDER BY id DESC LIMIT 1;

// select by write db
user, err := u.WithContext(ctx).WriteDB().Last()

// check error ErrRecordNotFound
errors.Is(err, gorm.ErrRecordNotFound)

根据主键检索

u := query.User

user, err := u.WithContext(ctx).Where(u.ID.Eq(10)).First()
// SELECT * FROM users WHERE id = 10;

users, err := u.WithContext(ctx).Where(u.ID.In(1,2,3)).Find()
// SELECT * FROM users WHERE id IN (1,2,3);

如果主键是字符串(例如像uuid)，查询将被写成如下：

user, err := u.WithContext(ctx).Where(u.ID.Eq("1b74413f-f3b8-409f-ac47-e8c062e3472a")).First()
// SELECT * FROM users WHERE id = "1b74413f-f3b8-409f-ac47-e8c062e3472a";

检索全部对象

u := query.User

// Get all records
users, err := u.WithContext(ctx).Find()
// SELECT * FROM users;

条件

字段查询接口

Gen 生成每个字段的安全类型接口，您可以使用它们生成SQL表达式

Field Type	Supported Interface
generic	IsNull/IsNotNull/Count/Eq/Neq/Gt/Gte/Lt/Lte/Like/Value/Sum/IfNull
int	Eq/Neq/Gt/Gte/Lt/Lte/In/NotIn/Between/NotBetween/Like/NotLike/Add/Sub/Mul/Div/Mod/FloorDiv/RightShift/LeftShift/BitXor/BitAnd/BitOr/BitFlip/Value/Zero/Sum/IfNull
uint	same with int
float	Eq/Neq/Gt/Gte/Lt/Lte/In/NotIn/Between/NotBetween/Like/NotLike/Add/Sub/Mul/Div/FloorDiv/Floor/Value/Zero/Sum/IfNull
string	Eq/Neq/Gt/Gte/Lt/Lte/Between/NotBetween/In/NotIn/Like/NotLike/Regexp/NotRegxp/FindInSet/FindInSetWith/Value/Zero/IfNull
bool	Not/Is/And/Or/Xor/BitXor/BitAnd/BitOr/Value/Zero
time	Eq/Neq/Gt/Gte/Lt/Lte/Between/NotBetween/In/NotIn/Add/Sub/Date/DateDiff/DateFormat/Now/CurDate/CurTime/DayName/MonthName/Month/Day/Hour/Minute/Second/MicroSecond/DayOfWeek/DayOfMonth/FromDays/FromUnixtime/Value/Zero/Sum/IfNull

以下是一些用法示例：

u := query.User

// Get first matched record
user, err := u.WithContext(ctx).Where(u.Name.Eq("modi")).First()
// SELECT * FROM users WHERE name = 'modi' ORDER BY id LIMIT 1;

// Get all matched records
users, err := u.WithContext(ctx).Where(u.Name.Neq("modi")).Find()
// SELECT * FROM users WHERE name <> 'modi';

// IN
users, err := u.WithContext(ctx).Where(u.Name.In("modi", "zhangqiang")).Find()
// SELECT * FROM users WHERE name IN ('modi','zhangqiang');

// LIKE
users, err := u.WithContext(ctx).Where(u.Name.Like("%modi%")).Find()
// SELECT * FROM users WHERE name LIKE '%modi%';

// AND
users, err := u.WithContext(ctx).Where(u.Name.Eq("modi"), u.Age.Gte(17)).Find()
// SELECT * FROM users WHERE name = 'modi' AND age >= 17;

// Time
users, err := u.WithContext(ctx).Where(u.Birthday.Gt(birthTime).Find()
// SELECT * FROM users WHERE birthday > '2000-01-01 00:00:00';

// BETWEEN
users, err := u.WithContext(ctx).Where(u.Birthday.Between(lastWeek, today)).Find()
// SELECT * FROM users WHERE birthday BETWEEN '2000-01-01 00:00:00' AND '2000-01-08 00:00:00';

Not 条件

构建 NOT 条件，用法与 Where 类似

u := query.User

user, err := u.WithContext(ctx).Not(u.Name.Eq("modi")).First()
// SELECT * FROM users WHERE NOT name = "modi" ORDER BY id LIMIT 1;

// Not In
users, err := u.WithContext(ctx).Not(u.Name.In("modi", "zhangqiang")).Find()
// SELECT * FROM users WHERE name NOT IN ("modi", "zhangqiang");

// Not In slice of primary keys
user, err := u.WithContext(ctx).Not(u.ID.In(1,2,3)).First()
// SELECT * FROM users WHERE id NOT IN (1,2,3) ORDER BY id LIMIT 1;

Or 条件

u := query.User

users, err := u.WithContext(ctx).Where(u.Role.Eq("admin")).Or(u.Role.Eq("super_admin")).Find()
// SELECT * FROM users WHERE role = 'admin' OR role = 'super_admin';

Group 条件

使用 Group 条件可以更轻松的编写复杂 SQL 查询

p := query.Pizza
pd := p.WithContext(ctx)

pizzas, err := pd.Where(
    pd.Where(p.Pizza.Eq("pepperoni")).
        Where(pd.Where(p.Size.Eq("small")).Or(p.Size.Eq("medium"))),
).Or(
    pd.Where(p.Pizza.Eq("hawaiian")).Where(p.Size.Eq("xlarge")),
).Find()

// SELECT * FROM `pizzas` WHERE (pizza = "pepperoni" AND (size = "small" OR size = "medium")) OR (pizza = "hawaiian" AND size = "xlarge")

查询特定字段

Select 允许您指定从数据库中取出哪些字段，默认情况下，GORM 会检索所有字段。

u := query.User

users, err := u.WithContext(ctx).Select(u.Name, u.Age).Find()
// SELECT name, age FROM users;

u.WithContext(ctx).Select(u.Age.Avg()).Rows()
// SELECT Avg(age) FROM users;

多字段IN

u := query.User

users, err := u.WithContext(ctx).Where(u.WithContext(ctx).Columns(u.ID, u.Name).In(field.Values([][]interface{}{{1, "modi"}, {2, "zhangqiang"}}))).Find()
// SELECT * FROM `users` WHERE (`id`, `name`) IN ((1,'humodi'),(2,'tom'));

JSON 查询

u := query.User

users, err := u.WithContext(ctx).Where(gen.Cond(datatypes.JSONQuery("attributes").HasKey("role"))...).Find()
// SELECT * FROM `users` WHERE JSON_EXTRACT(`attributes`,'$.role') IS NOT NULL;

Order

指定从数据库检索记录时的排序方式

u := query.User

users, err := u.WithContext(ctx).Order(u.Age.Desc(), u.Name).Find()
// SELECT * FROM users ORDER BY age DESC, name;

// Multiple orders
users, err := u.WithContext(ctx).Order(u.Age.Desc()).Order(u.Name).Find()
// SELECT * FROM users ORDER BY age DESC, name;

按字符串获取字段

u := query.User

orderCol, ok := u.GetFieldByName(orderColStr) // maybe orderColStr == "id"
if !ok {
  // User doesn't contains orderColStr
}

users, err := u.WithContext(ctx).Order(orderCol).Find()
// SELECT * FROM users ORDER BY age;

// OR Desc
users, err := u.WithContext(ctx).Order(orderCol.Desc()).Find()
// SELECT * FROM users ORDER BY age DESC;

Limit & Offset

Limit 指定要检索的最大记录数。 Offset 指定在开始返回记录前要跳过的记录数。

u := query.User

urers, err := u.WithContext(ctx).Limit(3).Find()
// SELECT * FROM users LIMIT 3;

// Cancel limit condition with -1
users, err := u.WithContext(ctx).Limit(10).Limit(-1).Find()
// SELECT * FROM users;

users, err := u.WithContext(ctx).Offset(3).Find()
// SELECT * FROM users OFFSET 3;

users, err := u.WithContext(ctx).Limit(10).Offset(5).Find()
// SELECT * FROM users OFFSET 5 LIMIT 10;

// Cancel offset condition with -1
users, err := u.WithContext(ctx).Offset(10).Offset(-1).Find()
// SELECT * FROM users;

Group By & Having

u := query.User

var users []struct {
    Name  string
    Total int
}
err := u.WithContext(ctx).Select(u.Name, u.ID.Count().As("total")).Group(u.Name).Scan(&users)
// SELECT name, count(id) as total FROM `users` GROUP BY `name`

err := u.WithContext(ctx).Select(u.Name, u.Age.Sum().As("total")).Where(u.Name.Like("%modi%")).Group(u.Name).Scan(&users)
// SELECT name, sum(age) as total FROM `users` WHERE name LIKE "%modi%" GROUP BY `name`

err := u.WithContext(ctx).Select(u.Name, u.Age.Sum().As("total")).Group(u.Name).Having(u.Name.Eq("group")).Scan(&users)
// SELECT name, sum(age) as total FROM `users` GROUP BY `name` HAVING name = "group"

rows, err := u.WithContext(ctx).Select(u.Birthday.As("date"), u.Age.Sum().As("total")).Group(u.Birthday).Rows()
for rows.Next() {
  ...
}

o := query.Order

rows, err := o.WithContext(ctx).Select(o.CreateAt.Date().As("date"), o.Amount.Sum().As("total")).Group(o.CreateAt.Date()).Having(u.Amount.Sum().Gt(100)).Rows()
for rows.Next() {
  ...
}

var results []struct {
    Date  time.Time
    Total int
}

o.WithContext(ctx).Select(o.CreateAt.Date().As("date"), o.WithContext(ctx).Amount.Sum().As("total")).Group(o.CreateAt.Date()).Having(u.Amount.Sum().Gt(100)).Scan(&results)

Distinct

从表中选择去重后的值

u := query.User

users, err := u.WithContext(ctx).Distinct(u.Name, u.Age).Order(u.Name, u.Age.Desc()).Find()

Distinct works with Pluck and Count too

Joins

指定 Join 条件

q := query
u := q.User
e := q.Email
c := q.CreditCard

type Result struct {
    Name  string
    Email string
    ID    int64
}

var result Result

err := u.WithContext(ctx).Select(u.Name, e.Email).LeftJoin(e, e.UserID.EqCol(u.ID)).Scan(&result)
// SELECT users.name, emails.email FROM `users` left join emails on emails.user_id = users.id

// self join
var result Result
u2 := u.As("u2")
err := u.WithContext(ctx).Select(u.Name, u2.ID).LeftJoin(u2, u2.ID.EqCol(u.ID)).Scan(&result)
// SELECT users.name, u2.id FROM `users` left join `users` u2 on u2.id = users.id

//join with sub query
var result Result
e2 := e.As("e2")
err := u.WithContext(ctx).Select(u.Name, e2.Email).LeftJoin(e.WithContext(ctx).Select(e.Email, e.UserID).Where(e.UserID.Gt(100)).As("e2"), e2.UserID.EqCol(u.ID)).Scan(&result)
// SELECT users.name, e2.email FROM `users` left join (select email,user_id from emails  where user_id > 100) as e2 on e2.user_id = users.id

rows, err := u.WithContext(ctx).Select(u.Name, e.Email).LeftJoin(e, e.UserID.EqCol(u.ID)).Rows()
for rows.Next() {
  ...
}

var results []Result

err := u.WithContext(ctx).Select(u.Name, e.Email).LeftJoin(e, e.UserID.EqCol(u.ID)).Scan(&results)

// multiple joins with parameter
users := u.WithContext(ctx).Join(e, e.UserID.EqCol(u.id), e.Email.Eq("modi@example.org")).Join(c, c.UserID.EqCol(u.ID)).Where(c.Number.Eq("411111111111")).Find()

新建字段

有时您可能需要为动态的 SQL 生成创建一个动态字段

Field Type	Create Function
generic	NewField
int	NewInt/NewInt8/…/NewInt64
uint	NewUint/NewUint8/…/NewUint64
float	NewFloat32/NewFloat64
string	NewString/NewBytes
bool	NewBool
time	NewTime

用法示例：

Generic Fields

import "gorm.io/gen/field"

// create a new generic field map to `generic_a`
f := field.NewField("table_name", "generic")
// `table_name`.`generic` IS NULL
f.IsNull()

// compare fields
id := field.NewField("user", "id")
anotherID := field.NewField("another", "id")
// `user`.`id` = `another`.`id`
id.EqCol(anotherID)

`int/uint/float` Fields

// int field
f := field.NewInt("user", "id")
// `user`.`id` = 123
f.Eq(123)
// `user`.`id` DESC
f.Desc()
// `user`.`id` AS `user_id`
f.As("user_id")
// COUNT(`user`.`id`)
f.Count()
// SUM(`user`.`id`)
f.Sum()
// SUM(`user`.`id`) > 123
f.Sum().Gt(123)
// ((`user`.`id`+1)*2)/3
f.Add(1).Mul(2).Div(3),
// `user`.`id` <<< 3
f.LeftShift(3)

String Fields

name := field.NewString("user", "name")
// `user`.`name` = "modi"
name.Eq("modi")
// `user`.`name` LIKE %modi%
name.Like("%modi%")
// `user`.`name` REGEXP .*
name.Regexp(".*")
// `user`.`name` FIND_IN_SET(`name`,"modi,jinzhu,zhangqiang")
name.FindInSet("modi,jinzhu,zhangqiang")
// `user`.`name` CONCAT("[",name,"]")
name.Concat("[", "]")

Time Fields

birth := field.NewTime("user", "biring")
// `user`.`birth` = ? (now)
birth.Eq(time.Now())
// DATE_ADD(`user`.`birth`, INTERVAL ? MICROSECOND)
birth.Add(time.Duration(time.Hour).Microseconds())
// DATE_FORMAT(`user`.`birth`, "%W %M %Y")
birth.DateFormat("%W %M %Y")

Bool Fields

active := field.NewBool("user", "active")
// `user`.`active` = TRUE
active.Is(true)
// NOT `user`.`active`
active.Not()
// `user`.`active` AND TRUE
active.And(true)

子查询

子查询可以嵌套在查询中，GEN 可以在使用 Dao 对象作为参数时生成子查询

o := query.Order
u := query.User

orders, err := o.WithContext(ctx).Where(o.WithContext(ctx).Columns(o.Amount).Gt(o.WithContext(ctx).Select(o.Amount.Avg())).Find()
// SELECT * FROM "orders" WHERE amount > (SELECT AVG(amount) FROM "orders");

subQuery := u.WithContext(ctx).Select(u.Age.Avg()).Where(u.Name.Like("name%"))
users, err := u.WithContext(ctx).Select(u.Age.Avg().As("avgage")).Group(u.Name).Having(u.WithContext(ctx).Columns(u.Age.Avg()).Gt(subQuery).Find()
// SELECT AVG(age) as avgage FROM `users` GROUP BY `name` HAVING AVG(age) > (SELECT AVG(age) FROM `users` WHERE name LIKE "name%")

// Select users with orders between 100 and 200
subQuery1 := o.WithContext(ctx).Select(o.ID).Where(o.UserID.EqCol(u.ID), o.Amount.Gt(100))
subQuery2 := o.WithContext(ctx).Select(o.ID).Where(o.UserID.EqCol(u.ID), o.Amount.Gt(200))
u.WithContext(ctx).Where(gen.Exists(subQuery1)).Not(gen.Exists(subQuery2)).Find()
// SELECT * FROM `users` WHERE EXISTS (SELECT `orders`.`id` FROM `orders` WHERE `orders`.`user_id` = `users`.`id` AND `orders`.`amount` > 100 AND `orders`.`deleted_at` IS NULL) AND NOT EXISTS (SELECT `orders`.`id` FROM `orders` WHERE `orders`.`user_id` = `users`.`id` AND `orders`.`amount` > 200 AND `orders`.`deleted_at` IS NULL) AND `users`.`deleted_at` IS NULL

From 子查询

GORM 允许您在 Table 方法中使用子查询作为表查询，例如：

u := query.User
p := query.Pet

users, err := gen.Table(u.WithContext(ctx).Select(u.Name, u.Age).As("u")).Where(u.Age.Eq(18)).Find()
// SELECT * FROM (SELECT `name`,`age` FROM `users`) as u WHERE `age` = 18

subQuery1 := u.WithContext(ctx).Select(u.Name)
subQuery2 := p.WithContext(ctx).Select(p.Name)
users, err := gen.Table(subQuery1.As("u"), subQuery2.As("p")).Find()
db.Table("(?) as u, (?) as p", subQuery1, subQuery2).Find(&User{})
// SELECT * FROM (SELECT `name` FROM `users`) as u, (SELECT `name` FROM `pets`) as p

FirstOrInit

如果没有找到记录，可以使用包含更多的属性的结构体初始化 user，Attrs 不会被用于生成查询 SQL

// User not found, initialize it with given conditions and Attrs
u.WithContext(ctx).Attrs(field.Attrs(&model.User{Age: 20})).Where(u.Name.Eq("non_existing")).FirstOrInit()
// SELECT * FROM USERS WHERE name = 'non_existing' ORDER BY id LIMIT 1;
// user -> User{Name: "non_existing", Age: 20}

// User not found, initialize it with given conditions and Attrs
u.WithContext(ctx).Attrs(u.Age.Value(20).Where(u.Name.Eq("non_existing")).FirstOrInit()
// SELECT * FROM USERS WHERE name = 'non_existing' ORDER BY id LIMIT 1;
// user -> User{Name: "non_existing", Age: 20}

// Found user with `name` = `gen`, attributes will be ignored
u.WithContext(ctx).Attrs(field.Attrs(&model.User{Age: 20})).Where(u.Name.Eq("gen")).FirstOrInit()
// SELECT * FROM USERS WHERE name = 'gen' ORDER BY id LIMIT 1;
// user -> User{ID: 111, Name: "gen", Age: 18}

不管是否找到记录，Assign 都会将属性赋值给 struct，但这些属性不会被用于生成查询 SQL，也不会被保存到数据库

// User not found, initialize it with give conditions and Assign attributes
u.WithContext(ctx).Assign(field.Attrs(map[string]interface{}{"age": 20})).Where(u.Name.Eq("non_existing")).FirstOrInit()
// user -> User{Name: "non_existing", Age: 20}

// Found user with `name` = `gen`, update it with Assign attributes
u.WithContext(ctx).Assign(field.Attrs(&model.User{Name: "gen_assign"}).Select(dal.User.ALL)).Where(u.Name.Eq("gen")).FirstOrInit()

// SELECT * FROM USERS WHERE name = gen' ORDER BY id LIMIT 1;
// user -> User{ID: 111, Name: "gen", Age: 20}

FirstOrCreate

获取匹配的第一条记录或者根据给定条件创建一条新纪录（仅 struct, map 条件有效），RowsAffected 返回创建、更新的记录数


//通过`name` = `gen`查找用户
result:=u.WithContext(ctx).Where(u.Name.Eq(jinzhu)).FirstOrCreate()
// 用户信息 -> User{ID: 111, Name: "gen", "Age": 18}
// result.RowsAffected // => 0

如果没有找到记录，可以使用包含更多的属性的结构体创建记录，Attrs 不会被用于生成查询 SQL 。

// User not found, create it with give conditions and Attrs
u.WithContext(ctx).Attrs(field.Attrs(&model.User{Age: 20})).Where(u.Name.Eq("non_existing")).FirstOrCreate()
// SELECT * FROM users WHERE name = 'non_existing' ORDER BY id LIMIT 1;
// INSERT INTO "users" (name, age) VALUES ("non_existing", 20);
// user -> User{ID: 112, Name: "non_existing", Age: 20}

// Found user with `name` = `gen`, attributes will be ignored
u.WithContext(ctx).Attrs(field.Attrs(&model.User{Age: 20})).Where(u.Name.Eq("gen")).FirstOrCreate()
// SELECT * FROM users WHERE name = 'gen' ORDER BY id LIMIT 1;
// user -> User{ID: 111, Name: "gen", Age: 18}

不管是否找到记录，Assign 都会将属性赋值给 struct，并将结果写回数据库

// User not found, initialize it with give conditions and Assign attributes
u.WithContext(ctx).Assign(field.Attrs(&model.User{Age: 20})).Where(u.Name.Eq("non_existing")).FirstOrCreate()
// SELECT * FROM users WHERE name = 'non_existing' ORDER BY id LIMIT 1;
// INSERT INTO "users" (name, age) VALUES ("non_existing", 20);
// user -> User{ID: 112, Name: "non_existing", Age: 20}

// Found user with `name` = `gen`, update it with Assign attributes
u.WithContext(ctx).Assign(field.Attrs(&model.User{Age: 20})).Where(u.Name.Eq("gen")).FirstOrCreate()
// SELECT * FROM users WHERE name = 'gen' ORDER BY id LIMIT 1;
// UPDATE users SET age=20 WHERE id = 111;
// user -> User{ID: 111, Name: "gen", Age: 20}

// Found user with `name` = `gen`, update it with Assign attributes
u.WithContext(ctx).Assign(u.Age.Value(20)).Where(u.Name.Eq("gen")).FirstOrCreate()
// SELECT * FROM users WHERE name = 'gen' ORDER BY id LIMIT 1;
// UPDATE users SET age=20 WHERE id = 111;
// user -> User{ID: 111, Name: "gen", Age: 20}

Struct & Map Conditions

// Struct
u.WithContext(ctx).Where(field.Attrs(&User{Name: "gen", Age: 20})).First()
// SELECT * FROM users WHERE name = "gen" AND age = 20 ORDER BY id LIMIT 1;

// Map
u.WithContext(ctx).Where(field.Attrs(map[string]interface{}{"name": "gen", "age": 20})).Find()
// SELECT * FROM users WHERE name = "gen" AND age = 20;

注意当使用 struct 进行查询时，GORM GEN只会使用非零值字段进行查询。这意味着如果您的字段值为 0、''、false 或其他零值，该字段不会被用于构建查询条件，例如：

u.WithContext(ctx).Where(field.Attrs(&User{Name: "gen", Age: 0})).Find()
// SELECT * FROM users WHERE name = "gen";

如果想要在查询条件中包含零值，你可以使用 map ，其会包含所有的键值对查询条件，例如：

u.WithContext(ctx).Where(field.Attrs(map[string]interface{}{"name": "gen", "age": 0})).Find()
// SELECT * FROM users WHERE name = "gen" AND age = 0;

了解更多的细节，请阅读 Specify Struct search fields 。

Specify Struct search fields

当使用 struct 进行查询时，你可以通过向 Select() 、Omit() 传入字段名来指定查询条件，例如：

u.WithContext(ctx).Where(field.Attrs(&User{Name: "gen"}).Select(u.Name,u.Age)).Find()
// SELECT * FROM users WHERE name = "gen" AND age = 0;

u.WithContext(ctx).Where(field.Attrs(&User{Name: "gen"}).Select(u.Age)).Find()
// SELECT * FROM users WHERE age = 0;

Gen Query

检索单个对象

根据主键检索

检索全部对象

条件

字段查询接口

Not 条件

Or 条件

Group 条件

查询特定字段

多字段IN

JSON 查询

Order

Limit & Offset

Group By & Having

Distinct

Joins

新建字段

Generic Fields

`int/uint/float` Fields

String Fields

Time Fields

Bool Fields

子查询

From 子查询

FirstOrInit

FirstOrCreate

Struct & Map Conditions

Specify Struct search fields

Platinum Sponsors

Gold Sponsors

Platinum Sponsors

Gold Sponsors

检索单个对象

根据主键检索

检索全部对象

条件

字段查询接口

Not 条件

Or 条件

Group 条件

查询特定字段

多字段IN

JSON 查询

Order

Limit & Offset

Group By & Having

Distinct

Joins

新建字段

Generic Fields

int/uint/float Fields

String Fields

Time Fields

Bool Fields

子查询

From 子查询

FirstOrInit

FirstOrCreate

Struct & Map Conditions

Specify Struct search fields

Platinum Sponsors

Gold Sponsors

Platinum Sponsors

Gold Sponsors

`int/uint/float` Fields