【开发神器一键生成代码，让开发更高效！Gorm GEN 零基础教程-每日运维

GORM/GEN

基于 GORM, 更安全更友好的ORM工具。

Overview

自动生成CRUD和DIY方法
自动根据表结构生成model
完全兼容GORM
更安全、更友好
多种生成代码模式

安装

安装GEN前，需要安装好GO并配置你的工作环境。

1.安装完Go(version 1.14+)之后，通过下面的命令安装gen。

go get -u gorm.io/gen

2.导入到你的工程:

import "gorm.io/gen"

快速开始

注⚠️: 这里所有的教程都是在 WithContext 模式下写的. 如果你用的是WithoutContext 模式,则可以删除所有的 WithContext(ctx) ，这样代码看起来会更简洁.

# assume the following code in generate.go file
$ cat generate.go

package main

import "gorm.io/gen"

// generate code
func main() {
    // specify the output directory (default: "./query")
    // ### if you want to query without context constrain, set mode gen.WithoutContext ###
    g := gen.NewGenerator(gen.Config{
        OutPath: "../dal/query",
        /* Mode: gen.WithoutContext|gen.WithDefaultQuery*/
        //if you want the nullable field generation property to be pointer type, set FieldNullable true
        /* FieldNullable: true,*/
        //if you want to generate index tags from database, set FieldWithIndexTag true
        /* FieldWithIndexTag: true,*/
        //if you want to generate type tags from database, set FieldWithTypeTag true
        /* FieldWithTypeTag: true,*/
        //if you need unit tests for query code, set WithUnitTest true
        /* WithUnitTest: true, */
    })
  
    // reuse the database connection in Project or create a connection here
    // if you want to use GenerateModel/GenerateModelAs, UseDB is necessray or it will panic
    // db, _ := gorm.Open(mysql.Open("root:@(127.0.0.1:3306)/demo?&parseTime=True&loc=Local"))
    g.UseDB(db)
  
    // apply basic crud api on structs or table models which is specified by table name with function
    // GenerateModel/GenerateModelAs. And generator will generate table models' code when calling Excute.
    g.ApplyBasic(model.User{}, g.GenerateModel("company"), g.GenerateModelAs("people", "Person", gen.FieldIgnore("address")))
    
    // apply diy interfaces on structs or table models
    g.ApplyInterface(func(method model.Method) {}, model.User{}, g.GenerateModel("company"))

    // execute the action of code generation
    g.Execute()
}

生成Model:

gen.WithoutContext 非 WithContext 模式生成
gen.WithDefaultQuery 生成默认全局查询变量

项目路径

最佳实践项目模板:

demo
├── cmd
│   └── generate
│       └── generate.go # execute it will generate codes
├── dal
│   ├── dal.go # create connections with database server here
│   ├── model
│   │   ├── method.go # DIY method interfaces
│   │   └── model.go  # store struct which corresponding to the database table
│   └── query  # generated code's directory
|       ├── user.gen.go # generated code for user
│       └── gen.go # generated code
├── biz
│   └── query.go # call function in dal/gorm_generated.go and query databases
├── config
│   └── config.go # DSN for database server
├── generate.sh # a shell to execute cmd/generate
├── go.mod
├── go.sum
└── main.go

API 示例

生成

生成Model

// generate a model struct map to table `people` in database
g.GenerateModel("people")

// generate a struct and specify struct's name
g.GenerateModelAs("people", "People")

// add option to ignore field
g.GenerateModel("people", gen.FieldIgnore("address"), gen.FieldType("id", "int64"))

// generate all tables, ex: g.ApplyBasic(g.GenerateAllTable()...)
g.GenerateAllTable()

字段生成 Options

FieldNew           // create new field
FieldIgnore        // ignore field
FieldIgnoreReg     // ignore field (match with regexp)
FieldRename        // rename field in struct
FieldType          // specify field type
FieldTypeReg       // specify field type (match with regexp)
FieldTag           // specify gorm and json tag
FieldJSONTag       // specify json tag
FieldGORMTag       // specify gorm tag
FieldNewTag        // append new tag
FieldNewTagWithNS  // specify new tag with name strategy
FieldTrimPrefix    // trim column prefix
FieldTrimSuffix    // trim column suffix
FieldAddPrefix     // add prefix to struct member's name
FieldAddSuffix     // add suffix to struct member's name
FieldRelate        // specify relationship with other tables
FieldRelateModel   // specify relationship with exist models

类型映射

自定义数据库字段类型和go类型的映射关系.

dataMap := map[string]func(detailType string) (dataType string){
  "int": func(detailType string) (dataType string) { return "int64" },
  // bool mapping
  "tinyint": func(detailType string) (dataType string) {
    if strings.HasPrefix(detailType, "tinyint(1)") {
      return "bool"
    }
    return "int8"
  },
}

g.WithDataTypeMap(dataMap)

字段表达式

创建字段

实际上你需要手动创建字段，因为都会在生成代码自动创建。

Field Type	Detail Type	Create Function	Supported Query Method
generic	field	NewField	IsNull/IsNotNull/Count/Eq/Neq/Gt/Gte/Lt/Lte/Like
int	int/int8/.../int64	NewInt/NewInt8/.../NewInt64	Eq/Neq/Gt/Gte/Lt/Lte/In/NotIn/Between/NotBetween/Like/NotLike/Add/Sub/Mul/Div/Mod/FloorDiv/RightShift/LeftShift/BitXor/BitAnd/BitOr/BitFlip
uint	uint/uint8/.../uint64	NewUint/NewUint8/.../NewUint64	same with int
float	float32/float64	NewFloat32/NewFloat64	Eq/Neq/Gt/Gte/Lt/Lte/In/NotIn/Between/NotBetween/Like/NotLike/Add/Sub/Mul/Div/FloorDiv
string	string/[]byte	NewString/NewBytes	Eq/Neq/Gt/Gte/Lt/Lte/Between/NotBetween/In(val/NotIn(val/Like/NotLike/Regexp/NotRegxp/FindInSet/FindInSetWith
bool	bool	NewBool	Not/Is/And/Or/Xor/BitXor/BitAnd/BitOr
time	time.Time	NewTime	Eq/Neq/Gt/Gte/Lt/Lte/Between/NotBetween/In/NotIn/Add/Sub

创建字段示例:

import "gorm.io/gen/field"

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

// create a field map to `id`
i := field.NewInt("user", "id")

// create a field map to `address`
s := field.NewString("user", "address")

// create a field map to `create_time`
t := field.NewTime("user", "create_time")

CRUD 接口

生成基础model user 和 DB.

// generated code
// generated code
// generated code
package query

import "gorm.io/gen"

// struct map to table `users` 
type user struct {
    gen.DO
    ID       field.Uint
    Name     field.String
    Age      field.Int
    Address  field.Field
    Birthday field.Time
}

// struct collection
type DB struct {
    db       *gorm.DB
    User     *user
}

创建

创建记录

// u refer to query.user
user := model.User{Name: "Modi", Age: 18, Birthday: time.Now()}

u := query.Use(db).User
err := u.WithContext(ctx).Create(&user) // pass pointer of data to Create

err // returns error

选择字段创建

自定义哪些字段需要插入。

u := query.Use(db).User
u.WithContext(ctx).Select(u.Name, u.Age).Create(&user)
// INSERT INTO `users` (`name`,`age`) VALUES ("modi", 18)

自定义创建时需要忽略的字段。

u := query.Use(db).User
u.WithContext(ctx).Omit(u.Name, u.Age).Create(&user)
// INSERT INTO `users` (`Address`, `Birthday`) VALUES ("2021-08-17 20:54:12.000", 18)

批量创建

Create 方法支持批量创建，参数只要是对应model的slice就可以. GORM会通过一条语句高效创建并返回所有的主键赋值给slice的Model.

var users = []model.User{{Name: "modi"}, {Name: "zhangqiang"}, {Name: "songyuan"}}
query.Use(db).User.WithContext(ctx).Create(&users)

for _, user := range users {
    user.ID // 1,2,3
}

CreateInBatches可以指定批量创建的大小, e.g:

var users = []User{{Name: "modi_1"}, ...., {Name: "modi_10000"}}

// batch size 100
query.Use(db).User.WithContext(ctx).CreateInBatches(users, 100)

也可以通过全局配置方式，在初始化gorm时设置 CreateBatchSize in gorm.Config / gorm.Session

db, err := gorm.Open(sqlite.Open("gorm.db"), &gorm.Config{
    CreateBatchSize: 1000,
})
// OR
db = db.Session(&gorm.Session{CreateBatchSize: 1000})

u := query.NewUser(db)

var users = []User{{Name: "modi_1"}, ...., {Name: "modi_5000"}}

u.WithContext(ctx).Create(&users)
// INSERT INTO users xxx (5 batches)

查询

单个数据查询

自动生成 First, Take, Last 三个查询单条数据的方法。执行的sql后面会自动添加 LIMIT 1 ，如果没有查到数据会返回错误： ErrRecordNotFound 。

u := query.Use(db).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;

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

根据主键查询数据

u := query.Use(db).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);

如果是string类型的主键，比如UUID等:

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";

查询所有数据

u := query.Use(db).User

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

条件

基础查询

u := query.Use(db).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

u := query.Use(db).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

u := query.Use(db).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

组合where或or 构建复杂查询

p := query.Use(db).Pizza

pizzas, err := p.WithContext(ctx).Where(
    p.WithContext(ctx).Where(p.Pizza.Eq("pepperoni")).
        Where(p.Where(p.Size.Eq("small")).Or(p.Size.Eq("medium"))),
).Or(
    p.WithContext(ctx).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")

指定字段查询

通过Select 可以选择你要查询的字段，否则就是查询所有字段。

u := query.Use(db).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;

元组查询

例如多字段IN

u := query.Use(db).User

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

JSON 查询

u := query.Use(db).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

指定查询的排序方式

u := query.Use(db).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;

Limit & Offset

分页查询，Limit限制最大条数，Offset指定数据的其实位置。

u := query.Use(db).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.Use(db).User

type Result struct {
    Date  time.Time
    Total int
}

var result Result

err := u.WithContext(ctx).Select(u.Name, u.Age.Sum().As("total")).Where(u.Name.Like("%modi%")).Group(u.Name).Scan(&result)
// 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(&result)
// 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.Use(db).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 []Result

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

u := query.Use(db).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

联表查询，Join是指inner join,还有LeftJoin和RightJoin

u := query.Use(db).User
e := query.Use(db).Email
c := query.Use(db).CreditCard

type Result struct {
    Name  string
    Email string
}

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

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()

子查询

o := query.Use(db).Order
u := query.Use(db).User

orders, err := o.WithContext(ctx).Where(u.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.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%")

From 子查询

通过Table方法构建出的子查询，可以直接放到From语句中:

u := query.Use(db).User
p := query.Use(db).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

更新子查询

通过子查询更新表字段

u := query.Use(db).User
c := query.Use(db).Company

u.WithContext(ctx).Update(u.CompanyName, c.Select(c.Name).Where(c.ID.EqCol(u.CompanyID)))
// UPDATE "users" SET "company_name" = (SELECT name FROM companies WHERE companies.id = users.company_id);

u.WithContext(ctx).Where(u.Name.Eq("modi")).Update(u.CompanyName, c.Select(c.Name).Where(c.ID.EqCol(u.CompanyID)))

多字段更新子查询

针对mysql提供同时更新多个字段的子查询:

u := query.Use(db).User
c := query.Use(db).Company

ua := u.As("u")
ca := u.As("c")

ua.WithContext(ctx).UpdateFrom(ca.WithContext(ctx).Select(c.ID, c.Address, c.Phone).Where(c.ID.Gt(100))).
Where(ua.CompanyID.EqCol(ca.ID)).
UpdateSimple(
  ua.Address.SetCol(ca.Address),
  ua.Phone.SetCol(ca.Phone),
)
// UPDATE `users` AS `u`,(
//   SELECT `company`.`id`,`company`.`address`,`company`.`phone` 
//   FROM `company` WHERE `company`.`id` > 100 AND `company`.`deleted_at` IS NULL
// ) AS `c` 
// SET `u`.`address`=`c`.`address`,`c`.`phone`=`c`.`phone`,`updated_at`='2021-11-11 11:11:11.111'
// WHERE `u`.`company_id` = `c`.`id`

事务

多个操作需要在一个事务中完成的情况.

q := query.Use(db)

q.Transaction(func(tx *query.Query) error {
  if _, err := tx.User.WithContext(ctx).Where(tx.User.ID.Eq(100)).Delete(); err != nil {
    return err
  }
  if _, err := tx.Article.WithContext(ctx).Create(&model.User{Name:"modi"}); err != nil {
    return err
  }
  return nil
})

嵌套事务

GEN 支持潜逃事务，在一个大事务中嵌套子事务。

q := query.Use(db)

q.Transaction(func(tx *query.Query) error {
  tx.User.WithContext(ctx).Create(&user1)

  tx.Transaction(func(tx2 *query.Query) error {
    tx2.User.WithContext(ctx).Create(&user2)
    return errors.New("rollback user2") // Rollback user2
  })

  tx.Transaction(func(tx2 *query.Query) error {
    tx2.User.WithContext(ctx).Create(&user3)
    return nil
  })

  return nil
})

// Commit user1, user3

手动事务

q := query.Use(db)

// begin a transaction
tx := q.Begin()

// do some database operations in the transaction (use 'tx' from this point, not 'db')
tx.User.WithContext(ctx).Create(...)

// ...

// rollback the transaction in case of error
tx.Rollback()

// Or commit the transaction
tx.Commit()

For example:

q := query.Use(db)

func doSomething(ctx context.Context, users ...*model.User) (err error) {
    tx := q.Begin()
    defer func() {
        if recover() != nil || err != nil {
            _ = tx.Rollback()
        }
    }()

    err = tx.User.WithContext(ctx).Create(users...)
    if err != nil {
        return
    }
    return tx.Commit()
}

保存点

SavePoint, RollbackTo 可以保存或者回滚事务点:

tx := q.Begin()
txCtx = tx.WithContext(ctx)

txCtx.User.Create(&user1)

tx.SavePoint("sp1")
txCtx.Create(&user2)
tx.RollbackTo("sp1") // Rollback user2

tx.Commit() // Commit user1

Advanced Query

迭代

GEN支持通过Row迭代取值

u := query.Use(db).User
do := u.WithContext(ctx)
rows, err := do.Where(u.Name.Eq("modi")).Rows()
defer rows.Close()

for rows.Next() {
    var user User
    // ScanRows is a method of `gorm.DB`, it can be used to scan a row into a struct
    do.ScanRows(rows, &user)

    // do something
}

批量查询

u := query.Use(db).User

// batch size 100
err := u.WithContext(ctx).Where(u.ID.Gt(9)).FindInBatches(&results, 100, func(tx gen.Dao, batch int) error {
    for _, result := range results {
      // batch processing found records
    }
  
    // build a new `u` to use it's api
    // queryUsery := query.NewUser(tx.UnderlyingDB())

    tx.Save(&results)

    batch // Batch 1, 2, 3

    // returns error will stop future batches
    return nil
})

Pluck

从数据库中查询单个列并扫描成一个切片或者基础类型

u := query.Use(db).User

var ages []int64
u.WithContext(ctx).Pluck(u.Age, &ages)

var names []string
u.WithContext(ctx).Pluck(u.Name, &names)

// Distinct Pluck
u.WithContext(ctx).Distinct().Pluck(u.Name, &names)
// SELECT DISTINCT `name` FROM `users`

// Requesting more than one column, use `Scan` or `Find` like this:
db.WithContext(ctx).Select(u.Name, u.Age).Scan(&users)
users, err := db.Select(u.Name, u.Age).Find()

Scopes

可以声明一些常用的或者公用的条件方法，然后通过Scopes 查询

o := query.Use(db).Order

func AmountGreaterThan1000(tx gen.Dao) gen.Dao {
    return tx.Where(o.Amount.Gt(1000))
}

func PaidWithCreditCard(tx gen.Dao) gen.Dao {
    return tx.Where(o.PayModeSign.Eq("C"))
}

func PaidWithCod(tx gen.Dao) gen.Dao {
    return tx.Where(o.PayModeSign.Eq("C"))
}

func OrderStatus(status []string) func (tx gen.Dao) gen.Dao {
    return func (tx gen.Dao) gen.Dao {
      return tx.Where(o.Status.In(status...))
    }
}

orders, err := o.WithContext(ctx).Scopes(AmountGreaterThan1000, PaidWithCreditCard).Find()
// Find all credit card orders and amount greater than 1000

orders, err := o.WithContext(ctx).Scopes(AmountGreaterThan1000, PaidWithCod).Find()
// Find all COD orders and amount greater than 1000

orders, err := o.WithContext(ctx).Scopes(AmountGreaterThan1000, OrderStatus([]string{"paid", "shipped"})).Find()
// Find all paid, shipped orders that amount greater than 1000

Count

u := query.Use(db).User

count, err := u.WithContext(ctx).Where(u.Name.Eq("modi")).Or(u.Name.Eq("zhangqiang")).Count()
// SELECT count(1) FROM users WHERE name = 'modi' OR name = 'zhangqiang'

count, err := u.WithContext(ctx).Where(u.Name.Eq("modi")).Count()
// SELECT count(1) FROM users WHERE name = 'modi'; (count)

// Count with Distinct
u.WithContext(ctx).Distinct(u.Name).Count()
// SELECT COUNT(DISTINCT(`name`)) FROM `users`

FirstOrInit

获取匹配的第一条数据或用给定条件初始化一个实例

u := query.Use(db).User

// User not found, initialize it with give conditions
user, err := u.WithContext(ctx).Where(u.Name.Eq("non_existing")).FirstOrInit()
// user -> User{Name: "non_existing"}

// Found user with `name` = `modi`
user, err := u.WithContext(ctx).Where(u.Name.Eq("modi")).FirstOrInit()
// user -> User{ID: 1, Name: "modi", Age: 17}

如果希望初始化的实例包含一些非查询条件的属性，则可以通过Attrs指定

u := query.Use(db).User

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

// Found user with `name` = `modi`, attributes will be ignored
user, err := u.WithContext(ctx).Where(u.Name.Eq("modi")).Attrs(u.Age.Value(20)).FirstOrInit()
// SELECT * FROM USERS WHERE name = modi' ORDER BY id LIMIT 1;
// user -> User{ID: 1, Name: "modi", Age: 17}

Assign 则是无论有没有找到记录，都用指定的属性进行覆盖已有的属性

// User not found, initialize it with give conditions and Assign attributes
user, err := u.WithContext(ctx).Where(u.Name.Eq("non_existing")).Assign(u.Age.Value(20)).FirstOrInit()
// user -> User{Name: "non_existing", Age: 20}

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

FirstOrCreate

获取第一条匹配的记录或在给定条件下创建一条新记录

u := query.Use(db).User

// User not found, create a new record with give conditions
user, err := u.WithContext(ctx).Where(u.Name.Eq("non_existing")).FirstOrCreate()
// INSERT INTO "users" (name) VALUES ("non_existing");
// user -> User{ID: 112, Name: "non_existing"}

// Found user with `name` = `modi`
user, err := u.WithContext(ctx).Where(u.Name.Eq("modi")).FirstOrCreate()
// user -> User{ID: 111, Name: "modi", "Age": 18}

如果希望创建的实例包含一些非查询条件的属性，则可以通过Attrs指定

u := query.Use(db).User

// User not found, create it with give conditions and Attrs
user, err := u.WithContext(ctx).Where(u.Name.Eq("non_existing")).Attrs(u.Age.Value(20)).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` = `modi`, attributes will be ignored
user, err := u.WithContext(ctx).Where(u.Name.Eq("modi")).Attrs(u.Age.Value(20)).FirstOrCreate()
// SELECT * FROM users WHERE name = 'modi' ORDER BY id LIMIT 1;
// user -> User{ID: 111, Name: "modi", Age: 18}

Assign 则是无论有没有找到记录，都用指定的属性进行覆盖并且入库

u := query.Use(db).User

// User not found, initialize it with give conditions and Assign attributes
user, err := u.WithContext(ctx).Where(u.Name.Eq("non_existing")).Assign(u.Age.Value(20)).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` = `modi`, update it with Assign attributes
user, err := u.WithContext(ctx).Where(u.Name.Eq("modi")).Assign(u.Age.Value(20)).FirstOrCreate(&user)
// SELECT * FROM users WHERE name = 'modi' ORDER BY id LIMIT 1;
// UPDATE users SET age=20 WHERE id = 111;
// user -> User{ID: 111, Name: "modi", Age: 20}

关联

GEN将像GORM一样自动保存关联（(BelongsTo/HasOne/HasMany/Many2Many) 。

Relation

There are 4 kind of relationship.

const (
    HasOne    RelationshipType = RelationshipType(schema.HasOne)    // HasOneRel has one relationship
    HasMany   RelationshipType = RelationshipType(schema.HasMany)   // HasManyRel has many relationships
    BelongsTo RelationshipType = RelationshipType(schema.BelongsTo) // BelongsToRel belongs to relationship
    Many2Many RelationshipType = RelationshipType(schema.Many2Many) // Many2ManyRel many to many relationship
)

关联已经存在的Model

package model

// exist model
type Customer struct {
    gorm.Model
    CreditCards []CreditCard `gorm:"foreignKey:CustomerRefer"`
}

type CreditCard struct {
    gorm.Model
    Number        string
    CustomerRefer uint
}

GEN 会检查解析这些关联关系:

// specify model
g.ApplyBasic(model.Customer{}, model.CreditCard{})

// assoications will be detected and converted to code 
package query

type customer struct {
    ...
    CreditCards customerHasManyCreditCards
}

type creditCard struct{
    ...
}

和数据库表关联

必须使用 gen.FieldRelate声明

card := g.GenerateModel("credit_cards")
customer := g.GenerateModel("customers", gen.FieldRelate(field.HasMany, "CreditCards", b, 
    &field.RelateConfig{
        // RelateSlice: true,
        GORMTag: "foreignKey:CustomerRefer",
    }),
)

g.ApplyBasic(card, custormer)

GEN 会生成申明的关联属性:

// customers
type Customer struct {
    ID          int64          `gorm:"column:id;type:bigint(20) unsigned;primaryKey" json:"id"`
    CreatedAt   time.Time      `gorm:"column:created_at;type:datetime(3)" json:"created_at"`
    UpdatedAt   time.Time      `gorm:"column:updated_at;type:datetime(3)" json:"updated_at"`
    DeletedAt   gorm.DeletedAt `gorm:"column:deleted_at;type:datetime(3)" json:"deleted_at"`
    CreditCards []CreditCard   `gorm:"foreignKey:CustomerRefer" json:"credit_cards"`
}


// credit_cards
type CreditCard struct {
    ID            int64          `gorm:"column:id;type:bigint(20) unsigned;primaryKey" json:"id"`
    CreatedAt     time.Time      `gorm:"column:created_at;type:datetime(3)" json:"created_at"`
    UpdatedAt     time.Time      `gorm:"column:updated_at;type:datetime(3)" json:"updated_at"`
    DeletedAt     gorm.DeletedAt `gorm:"column:deleted_at;type:datetime(3)" json:"deleted_at"`
    CustomerRefer int64          `gorm:"column:customer_refer;type:bigint(20) unsigned" json:"customer_refer"`
}

如果是已经存在的关联model, 则可以用gen.FieldRelateModel 声明.

customer := g.GenerateModel("customers", gen.FieldRelateModel(field.HasMany, "CreditCards", model.CreditCard{}, 
    &field.RelateConfig{
        // RelateSlice: true,
        GORMTag: "foreignKey:CustomerRefer",
    }),
)

g.ApplyBasic(custormer)

关联配置

type RelateConfig struct {
    // specify field's type
    RelatePointer      bool // ex: CreditCard  *CreditCard
    RelateSlice        bool // ex: CreditCards []CreditCard
    RelateSlicePointer bool // ex: CreditCards []*CreditCard

    JSONTag      string // related field's JSON tag
    GORMTag      string // related field's GORM tag
    NewTag       string // related field's new tag
    OverwriteTag string // related field's tag
}

操作

跳过自动创建关联

user := model.User{
  Name:            "modi",
  BillingAddress:  Address{Address1: "Billing Address - Address 1"},
  ShippingAddress: Address{Address1: "Shipping Address - Address 1"},
  Emails:          []Email{
    {Email: "modi@example.com"},
    {Email: "modi-2@example.com"},
  },
  Languages:       []Language{
    {Name: "ZH"},
    {Name: "EN"},
  },
}

u := query.Use(db).User

u.WithContext(ctx).Select(u.Name).Create(&user)
// INSERT INTO "users" (name) VALUES ("jinzhu", 1, 2);

u.WithContext(ctx).Omit(u.BillingAddress.Field()).Create(&user)
// Skip create BillingAddress when creating a user

u.WithContext(ctx).Omit(u.BillingAddress.Field("Address1")).Create(&user)
// Skip create BillingAddress.Address1 when creating a user

u.WithContext(ctx).Omit(field.AssociationFields).Create(&user)
// Skip all associations when creating a user

Method Field will join a serious field name with ''.", for example: u.BillingAddress.Field("Address1", "Street") equals to BillingAddress.Address1.Street

查询关联

u := query.Use(db).User

languages, err = u.Languages.Model(&user).Find()

查询指定条件的关联

q := query.Use(db)
u := q.User

languages, err = u.Languages.Where(q.Language.Name.In([]string{"ZH","EN"})).Model(&user).Find()

添加关联

u := query.Use(db).User

u.Languages.Model(&user).Append(&languageZH, &languageEN)

u.Languages.Model(&user).Append(&Language{Name: "DE"})

u.CreditCards.Model(&user).Append(&CreditCard{Number: "411111111111"})

替换关联

u.Languages.Model(&user).Replace(&languageZH, &languageEN)

删除关联

删除存在的关联，不会删除数据

u := query.Use(db).User

u.Languages.Model(&user).Delete(&languageZH, &languageEN)

u.Languages.Model(&user).Delete([]*Language{&languageZH, &languageEN}...)

清楚关联

清楚所有的关联，不会删除数据

u.Languages.Model(&user).Clear()

统计关联

u.Languages.Model(&user).Count()

删除指定关联

删除制定条件数据并删除关联数据:

u := query.Use(db).User

// delete user's account when deleting user
u.Select(u.Account).Delete(&user)

// delete user's Orders, CreditCards relations when deleting user
db.Select(u.Orders.Field(), u.CreditCards.Field()).Delete(&user)

// delete user's has one/many/many2many relations when deleting user
db.Select(field.AssociationsFields).Delete(&user)

预加载

Preload

GEN 支持通过 Preload加载关联数据:

type User struct {
  gorm.Model
  Username string
  Orders   []Order
}

type Order struct {
  gorm.Model
  UserID uint
  Price  float64
}

q := query.Use(db)
u := q.User
o := q.Order

// Preload Orders when find users
users, err := u.WithContext(ctx).Preload(u.Orders).Find()
// SELECT * FROM users;
// SELECT * FROM orders WHERE user_id IN (1,2,3,4);

users, err := u.WithContext(ctx).Preload(u.Orders).Preload(u.Profile).Preload(u.Role).Find()
// 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

Preload All

clause.Associations 通过Preload 预加载所有的关联数据:

type User struct {
  gorm.Model
  Name       string
  CompanyID  uint
  Company    Company
  Role       Role
  Orders     []Order
}

users, err := u.WithContext(ctx).Preload(field.Associations).Find()

clause.Associations 不会加载嵌套关联, 潜逃关联家在可以用 Nested Preloading e.g:

users, err := u.WithContext(ctx).Preload(u.Orders.OrderItems.Product).Find()

根据条件预加载

q := query.Use(db)
u := q.User
o := q.Order

// Preload Orders with conditions
users, err := u.WithContext(ctx).Preload(u.Orders.On(o.State.NotIn("cancelled")).Find()
// SELECT * FROM users;
// SELECT * FROM orders WHERE user_id IN (1,2,3,4) AND state NOT IN ('cancelled');

users, err := u.WithContext(ctx).Where(u.State.Eq("active")).Preload(u.Orders.On(o.State.NotIn("cancelled")).Find()
// SELECT * FROM users WHERE state = 'active';
// SELECT * FROM orders WHERE user_id IN (1,2) AND state NOT IN ('cancelled');

users, err := u.WithContext(ctx).Preload(u.Orders.Order(o.ID.Desc(), o.CreateTime).Find()
// SELECT * FROM users;
// SELECT * FROM orders WHERE user_id IN (1,2) Order By id DESC, create_time;

users, err := u.WithContext(ctx).Preload(u.Orders.On(o.State.Eq("on")).Order(o.ID.Desc()).Find()
// SELECT * FROM users;
// SELECT * FROM orders WHERE user_id IN (1,2) AND state = "on" Order By id DESC;

users, err := u.WithContext(ctx).Preload(u.Orders.Clauses(hints.UseIndex("idx_order_id"))).Find()
// SELECT * FROM users;
// SELECT * FROM orders WHERE user_id IN (1,2) USE INDEX (`idx_order_id`);

潜逃预加载

db.Preload(u.Orders.OrderItems.Product).Preload(u.CreditCard).Find(&users)

// Customize Preload conditions for `Orders`
// And GEN won't preload unmatched order's OrderItems then
db.Preload(u.Orders.On(o.State.Eq("paid"))).Preload(u.Orders.OrderItems).Find(&users)

更新

更新单字段

Update方法更新单个字段。需要注意的是必须指定更新条件否则会报错ErrMissingWhereClause:

u := query.Use(db).User

// Update with conditions
u.WithContext(ctx).Where(u.Activate.Is(true)).Update(u.Name, "hello")
// UPDATE users SET name='hello', updated_at='2013-11-17 21:34:10' WHERE active=true;

// Update with conditions
u.WithContext(ctx).Where(u.Activate.Is(true)).Update(u.Age, u.Age.Add(1))
// or
u.WithContext(ctx).Where(u.Activate.Is(true)).UpdateSimple(u.Age.Add(1))
// UPDATE users SET age=age+1, updated_at='2013-11-17 21:34:10' WHERE active=true;

u.WithContext(ctx).Where(u.Activate.Is(true)).UpdateSimple(u.Age.Zero())
// UPDATE users SET age=0, updated_at='2013-11-17 21:34:10' WHERE active=true;

更新多字段

Updates 支持 struct 和 map[string]interface{}类型，更新多个字段，但是会忽略其中的零值属性

u := query.Use(db).User

// Update attributes with `map`
u.WithContext(ctx).Where(u.ID.Eq(111)).Updates(map[string]interface{}{"name": "hello", "age": 18, "active": false})
// UPDATE users SET name='hello', age=18, active=false, updated_at='2013-11-17 21:34:10' WHERE id=111;

// Update attributes with `struct`
u.WithContext(ctx).Where(u.ID.Eq(111)).Updates(model.User{Name: "hello", Age: 18, Active: false})
// UPDATE users SET name='hello', age=18, active=false, updated_at='2013-11-17 21:34:10' WHERE id=111;

// Update with expression
u.WithContext(ctx).Where(u.ID.Eq(111)).UpdateSimple(u.Age.Add(1), u.Number.Add(1))
// UPDATE users SET age=age+1,number=number+1, updated_at='2013-11-17 21:34:10' WHERE id=111;

u.WithContext(ctx).Where(u.Activate.Is(true)).UpdateSimple(u.Age.Value(17), u.Number.Zero(), u.Birthday.Null())
// UPDATE users SET age=17, number=0, birthday=NULL, updated_at='2013-11-17 21:34:10' WHERE active=true;

NOTE When update with struct, GEN will only update non-zero fields, you might want to use map to update attributes or use Select to specify fields to update

选择更新的字段

通过 Select, Omit选择需要更新的字段或者需要忽略更新的字段

u := query.Use(db).User

// Select with Map
// User's ID is `111`:
u.WithContext(ctx).Select(u.Name).Where(u.ID.Eq(111)).Updates(map[string]interface{}{"name": "hello", "age": 18, "active": false})
// UPDATE users SET name='hello' WHERE id=111;

u.WithContext(ctx).Omit(u.Name).Where(u.ID.Eq(111)).Updates(map[string]interface{}{"name": "hello", "age": 18, "active": false})
// UPDATE users SET age=18, active=false, updated_at='2013-11-17 21:34:10' WHERE id=111;

result, err := u.WithContext(ctx).Where(u.ID.Eq(111)).Updates(map[string]interface{}{"name": "hello", "age": 18, "active": false})

result.RowsAffected // affect rows number
err                 // error

删除

删除记录

e := query.Use(db).Email

// Email's ID is `10`
e.WithContext(ctx).Where(e.ID.Eq(10)).Delete()
// DELETE from emails where id = 10;

// Delete with additional conditions
e.WithContext(ctx).Where(e.ID.Eq(10), e.Name.Eq("modi")).Delete()
// DELETE from emails where id = 10 AND name = "modi";

result, err := e.WithContext(ctx).Where(e.ID.Eq(10), e.Name.Eq("modi")).Delete()

result.RowsAffected // affect rows number
err                 // error

根据主键删除

u.WithContext(ctx).Where(u.ID.In(1,2,3)).Delete()
// DELETE FROM users WHERE id IN (1,2,3);

批量删除

没有指定主键会删除松油匹配的数据

e := query.Use(db).Email

e.WithContext(ctx).Where(e.Name.Like("%modi%")).Delete()
// DELETE from emails where email LIKE "%modi%";

软删除

如果你的model中有gorm.DeletedAt 字段，则会自动执行软删除。也就是不会删除数据，只是把该字段的指设置为当前时间。

// Batch Delete
u.WithContext(ctx).Where(u.Age.Eq(20)).Delete()
// UPDATE users SET deleted_at="2013-10-29 10:23" WHERE age = 20;

// Soft deleted records will be ignored when querying
users, err := u.WithContext(ctx).Where(u.Age.Eq(20)).Find()
// SELECT * FROM users WHERE age = 20 AND deleted_at IS NULL;

If you don’t want to include gorm.Model, you can enable the soft delete feature like:

type User struct {
    ID      int
    Deleted gorm.DeletedAt
    Name    string
}

查询包含软删除的记录

可以通过 Unscoped实现

users, err := db.WithContext(ctx).Unscoped().Where(u.Age.Eq(20)).Find()
// SELECT * FROM users WHERE age = 20;

永久删除

通过 Unscoped可以直接删除数据，而不是标记删除

o.WithContext(ctx).Unscoped().Where(o.ID.Eq(10)).Delete()
// DELETE FROM orders WHERE id=10;

DIY 方法

接口定义

自定义方法，需要通过接口定义。在方上通过注释的方式描述具体的查询逻辑，复杂的可以直接用sql()，简单的直接用where()。
如果想要写一些原始注释，可以先写注释然后换行，在写sql或者where。

type Method interface {
    // where("name=@name and age=@age")
    SimpleFindByNameAndAge(name string, age int) (gen.T, error)

    // FindUserToMap query by id and return id->instance
    // 
    // sql(select * from users where id=@id)
    FindUserToMap(id int) (gen.M, error)
    
    // InsertValue insert into users (name,age) values (@name,@age)
    InsertValue(age int, name string) error
}

返回值可以是 gen.T/gen.M/gen.RowsAffected。 gen.T 表示单个model, []gen.T表示的是slice model，gen.M表示的是map[string]interface{},当然也可以是其他类型Gen不会转换。除了返回一个值外，还可以返回一个err。

语法

占位符

gen.T represents specified struct or table
gen.M represents map[string]interface
gen.RowsAffected represents SQL executed rowsAffected (type:int64)
@@table represents table's name (if method's parameter doesn't contains variable table, GEN will generate table from model struct)
@@ represents column's name or table's name
@ represents normal query variable

模板

逻辑操作必须包裹在{{}}中，如{{if}},结束语句必须是 {{end}}, 所有的语句都可以嵌套。

if/else if/else the condition accept a bool parameter or operation expression which conforms to Golang syntax.
where The where clause will be inserted only if the child elements return something. The key word and or or in front of clause will be removed. And and will be added automatically when there is no junction keyword between query condition clause.
Set The set clause will be inserted only if the child elements return something. The , in front of columns array will be removed.And , will be added automatically when there is no junction keyword between query coulmns.
... Coming soon

`If` clause

{{if cond1}}
    // do something here
{{else if cond2}}
    // do something here
{{else}}
    // do something here
{{end}}

Use case in raw SQL:

// select * from users where {{if name !=""}} name=@name{{end}}
methond(name string) (gen.T,error)

Use case in raw SQL template:

select * from @@table where
{{if age>60}}
    status="older"
{{else if age>30}}
    status="middle-ager"
{{else if age>18}}
    status="younger"
{{else}}
    {{if sex=="male"}}
        status="boys"
    {{else}}
        status="girls"
    {{end}}
{{end}}

`Where` clause

{{where}}
    // do something here
{{end}}

Use case in raw SQL

// select * from {{where}}id=@id{{end}}
methond(id int) error

Use case in raw SQL template

select * from @@table 
{{where}}
    {{if cond}}id=@id {{end}}
    {{if name != ""}}@@key=@value{{end}}
{{end}}

`Set` clause

{{set}}
    // sepecify update expression here
{{end}}

Use case in raw SQL

// update users {{set}}name=@name{{end}}
methond() error

Use case in raw SQL template

update @@table 
{{set}}
    {{if name!=""}} name=@name {{end}}
    {{if age>0}} age=@age {{end}}
{{end}}
where id=@id

Method interface example

type Method interface {
    // Where("name=@name and age=@age")
    SimpleFindByNameAndAge(name string, age int) (gen.T, error)
    
    // select * from users where id=@id
    FindUserToMap(id int) (gen.M, error)
    
    // sql(insert into @@table (name,age) values (@name,@age) )
    InsertValue(age int, name string) error
    
    // select name from @@table where id=@id
    FindNameByID(id int) string
    
    // select * from @@table
    //  {{where}}
    //      id>0
    //      {{if cond}}id=@id {{end}}
    //      {{if key!="" && value != ""}} or @@key=@value{{end}}
    //  {{end}}
    FindByIDOrCustom(cond bool, id int, key, value string) ([]gen.T, error)
    
    // update @@table
    //  {{set}}
    //      update_time=now()
    //      {{if name != ""}}
    //          name=@name
    //      {{end}}
    //  {{end}}
    //  {{where}}
    //      id=@id
    //  {{end}}
    UpdateName(name string, id int) (gen.RowsAffected,error)
}

智能选择字段

GEN 查询的时候会自动选择你的model定义的字段

type User struct {
  ID     uint
  Name   string
  Age    int
  Gender string
  // hundreds of fields
}

type APIUser struct {
  ID   uint
  Name string
}

type Method interface{
    // select * from user
    FindSome() ([]APIUser, error)
}

apiusers, err := u.WithContext(ctx).Limit(10).FindSome()
// SELECT `id`, `name` FROM `users` LIMIT 10

高级教程

Hints

Hints可以用来优化查询计划，比如指定索引后者强制索引等。

import "gorm.io/hints"

u := query.Use(db).User

users, err := u.WithContext(ctx).Clauses(hints.New("MAX_EXECUTION_TIME(10000)")).Find()
// SELECT * /*+ MAX_EXECUTION_TIME(10000) */ FROM `users`

import "gorm.io/hints"

u := query.Use(db).User

users, err := u.WithContext(ctx).Clauses(hints.UseIndex("idx_user_name")).Find()
// SELECT * FROM `users` USE INDEX (`idx_user_name`)

users, err := u.WithContext(ctx).Clauses(hints.ForceIndex("idx_user_name", "idx_user_id").ForJoin()).Find()
// SELECT * FROM `users` FORCE INDEX FOR JOIN (`idx_user_name`,`idx_user_id`)"

命令工具

安装gen命令行工具:

go install gorm.io/gen/tools/gentool@latest

使用参数:

$ gentool -h
Usage of gentool:
  -db string
      input mysql or postgres or sqlite or sqlserver. consult[https://gorm.io/docs/connecting_to_the_database.html] (default "mysql")
  -dsn string
      consult[https://gorm.io/docs/connecting_to_the_database.html]
  -fieldNullable
      generate with pointer when field is nullable
  -fieldWithIndexTag
      generate field with gorm index tag
  -fieldWithTypeTag
      generate field with gorm column type tag
  -modelPkgName string
      generated model code's package name
  -outFile string
      query code file name, default: gen.go
  -outPath string
      specify a directory for output (default "./dao/query")
  -tables string
      enter the required data table or leave it blank
  -withUnitTest
      generate unit test for query code

示例:

gentool -dsn "user:pwd@tcp(127.0.0.1:3306)/database?charset=utf8mb4&parseTime=True&loc=Local" -tables "orders,doctor"