240 lines
4.9 KiB
Markdown
240 lines
4.9 KiB
Markdown
# ent
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## Introduction
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ent是一个简单、功能强大的entity framework。下面，将会是一个ent的使用示例。
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### init project
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```bash
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go mod init entdemo
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```
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### 创建schema
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在entdemo目录下运行
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```bash
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go run -mod=mod entgo.io/ent/cmd/ent new User
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```
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上述命令会为`User`创建schema，创建位置位于`entdemo/ent/schema`目录下，`entdemo/ent/schema/user.go`文件内容如下：
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```go
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package schema
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import "entgo.io/ent"
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// User holds the schema definition for the User entity.
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type User struct {
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ent.Schema
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}
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// Fields of the User.
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func (User) Fields() []ent.Field {
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return nil
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}
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// Edges of the User.
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func (User) Edges() []ent.Edge {
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return nil
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}
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```
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### 向User实体中添加字段
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可以向User中添加两个字段，修改`Field`内容为如下：
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```go
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// Fields of the User.
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func (User) Fields() []ent.Field {
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return []ent.Field{
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field.Int("age").
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Positive(),
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field.String("name").
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Default("unknown"),
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}
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}
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```
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### go generate
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之后，可以调用`go generate`:
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```bash
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go generate ./ent
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```
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产生内容如下：
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```
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ent
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├── client.go
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├── config.go
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├── context.go
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├── ent.go
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├── generate.go
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├── mutation.go
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... truncated
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├── schema
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│ └── user.go
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├── tx.go
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├── user
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│ ├── user.go
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│ └── where.go
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├── user.go
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├── user_create.go
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├── user_delete.go
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├── user_query.go
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└── user_update.go
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```
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### 创建表并插入实体
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#### 创建表
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在执行完上述步骤后，可以通过如下代码来创建table
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```golang
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package main
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import (
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"context"
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"log"
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"entdemo/ent"
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_ "github.com/go-sql-driver/mysql"
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)
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func main() {
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client, err := ent.Open("mysql", "<user>:<pass>@tcp(<host>:<port>)/<database>?parseTime=True")
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if err != nil {
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log.Fatalf("failed opening connection to mysql: %v", err)
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}
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defer client.Close()
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// Run the auto migration tool.
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if err := client.Schema.Create(context.Background()); err != nil {
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log.Fatalf("failed creating schema resources: %v", err)
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}
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}
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```
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> 在执行上述代码前，需要先通过`create database xxx`先创建数据库。
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#### 插入实体
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通过如下代码，可以插入实体：
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```golang
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entdemo/start.go
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func CreateUser(ctx context.Context, client *ent.Client) (*ent.User, error) {
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u, err := client.User.
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Create().
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SetAge(30).
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SetName("a8m").
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Save(ctx)
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if err != nil {
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return nil, fmt.Errorf("failed creating user: %w", err)
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}
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log.Println("user was created: ", u)
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return u, nil
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}
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```
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### 查询实体
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查询实体可以通过如下代码实现：
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```golang
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func QueryUser(ctx context.Context, client *ent.Client) (ul []*ent.User, err error) {
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ul, err = client.User.
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Query().
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Where(
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user.Age(30),
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user.Name("a8m"),
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).All(ctx)
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if err != nil {
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log.Errorf("failed querying user: %v", err)
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}
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return
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}
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```
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### 添加关联关系
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另外创建两个实体`Car`和`Group`
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```bash
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go run -mod=mod entgo.io/ent/cmd/ent new Car Group
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```
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修改Car实体如下
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```golang
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package schema
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import (
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"entgo.io/ent"
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"entgo.io/ent/schema/field"
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)
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// Car holds the schema definition for the Car entity.
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type Car struct {
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ent.Schema
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}
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// Fields of the Car.
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func (Car) Fields() []ent.Field {
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return []ent.Field{
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field.String("model"),
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field.Time("registered_at"),
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}
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}
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// Edges of the Car.
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func (Car) Edges() []ent.Edge {
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return nil
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}
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```
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修改Group实体如下：
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```golang
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package schema
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import (
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"entgo.io/ent"
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"entgo.io/ent/schema/field"
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"regexp"
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)
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// Group holds the schema definition for the Group entity.
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type Group struct {
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ent.Schema
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}
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// Fields of the Group.
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func (Group) Fields() []ent.Field {
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return []ent.Field{
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field.String("name").
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// Regexp validation for group name.
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Match(regexp.MustCompile("[a-zA-Z_]+$")),
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}
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}
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// Edges of the Group.
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func (Group) Edges() []ent.Edge {
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return nil
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}
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```
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并修改User实体如下，为其新增`Edges`方法
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```golang
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package schema
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import (
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"entgo.io/ent"
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"entgo.io/ent/schema/edge"
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"entgo.io/ent/schema/field"
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)
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// User holds the schema definition for the User entity.
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type User struct {
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ent.Schema
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}
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// Fields of the User.
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func (User) Fields() []ent.Field {
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return []ent.Field{
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field.Int("age").Positive(),
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field.String("name").Default("unknown"),
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}
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}
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// Edges of the User.
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func (User) Edges() []ent.Edge {
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return []ent.Edge{
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edge.To("cars", Car.Type),
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}
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}
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```
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可知，Car和User实体的关系如下图所示：
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- 一个user可以拥有多个car
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<img loading="lazy" src="https://entgo.io/images/assets/re_user_cars.png" alt="er-user-cars" class="img_ev3q" id="er-user-cars">
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运行`go generate ./ent`后如下：
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```bash
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