Rust 建造者模式

在DDD中，DTO(数据传输对象)->BO(业务对象)、BO(业务对象)->PO(持久化对象，有的叫DO，即和数据表映射的实体)等等情况要做转换，这里提供以下转换方式

1、from或者try_from trait实现对象转换

需要转换对象满足接收对象的所有字段

客户定义

#[derive(Serialize, Deserialize, Clone, Debug)]
pub struct Customer {// uuidpub user_id: String,// 用户名pub username: String,// 邮件pub email: String,// 密码pub password: String,// 头像pub avatar: Option<String>,// 验证码pub verify_code: Option<String>,// 收货地址pub receive_address: Vec<ReceiveAddress>,
}

通过实现from trait，可以从Model转换为Customer

impl From<Model> for Customer {fn from(user: Model) -> Self {Customer {user_id: user.user_id,username: user.username,email: user.email,password: user.password,avatar: user.avatar,verify_code: user.verify_code,receive_address: user.receive_address,}}
}

实现了From trait默认自动实现Into trait，你可以通过以下两种方式实现对象转换，Try from trait用法一样，只是在转换失败时可以返回错误

// 使用from方法将Model实例转换为Customer实例
let customer_instance = Customer::from(model_instance);// 或者使用更简洁的into方法，它会自动调用对应的from方法
let another_customer_instance = model_instance.into();

但是这样不够优雅，很多时候DTO并不能满足领域对象的所有字段，数据对象也不能满足领域对象的所有字段，例如以上例子的验证码和收货地址，最初没有数据时需要设置默认值

// 转Bo
impl From<Model> for Customer {fn from(user: Model) -> Self {Customer {user_id: user.user_id,username: user.username,email: user.email,password: user.password,avatar: user.avatar,verify_code: None,receive_address: vec![],}}
}

当下一次从数据库中查到数据需要给收货地址赋值的情况下，这种方案就不适用了，可以使用以下建造者模式

2、链式调用

此时所有字段都是private的，通过builder去赋值

// 注意使用了Default，没有builder的值有默认值
#[derive(Serialize, Deserialize, Clone, Debug, Default)]
pub struct Customer {// uuidpub user_id: String,// 用户名pub username: String,// 邮件pub email: String,// 密码pub password: String,// 头像pub avatar: Option<String>,// 验证码pub verify_code: Option<String>,// 收货地址pub receive_address: Vec<ReceiveAddress>,
}
impl Customer {// new默认值pub fn new() -> Self {Self {user_id: String::new(),username: String::new(),email: String::new(),password: String::new(),avatar: None,verify_code: None,receive_address: Vec::new(),}}pub fn user_id(mut self, user_id: String) -> Self {self.user_id = user_id;self}pub fn username(mut self, username: String) -> Self {self.username = username;self}pub fn email(mut self, email: String) -> Self {self.email = email;self}pub fn password(mut self, password: String) -> Self {self.password = password;self}pub fn avatar(mut self, avatar: Option<String>) -> Self {self.avatar = avatar;self}pub fn verify_code(mut self, verify_code: Option<String>) -> Self {self.verify_code = verify_code;self}pub fn receive_address(mut self, receive_address: Vec<ReceiveAddress>) -> Self {self.receive_address = receive_address;self}
}

使用

    let customer = Customer::new().user_id("123".to_string()).username("张三".to_string()).email("<EMAIL>".to_string());let customer = customer.avatar(Some("https://www.baidu.com".to_string()));print!("{:?}\n", customer);//Customer { user_id: "123", username: "张三", email: "<EMAIL>", password: "", avatar: Some("https://www.baidu.com"), verify_code: None, receive_address: [] }// 修改原有对象let customer = customer.email("[e-mail]".to_string());println!("{:?}", customer);//Customer { user_id: "123", username: "张三", email: "[e-mail]", password: "", avatar: Some("https://www.baidu.com"), verify_code: None, receive_address: [] }

这种方式容易造成意外修改的传播，不推荐

3、建造者模式实现对象转换

在Java中很简单，加上@Builder注解即可

@Builder
public class User {private UserLastname lastname;private UserFirstname firstname;private UserEmail email;private UserPublicId userPublicId;private UserImageUrl imageUrl;private Instant lastModifiedDate;private Instant createdDate;private Set<Authority> authorities;private Long dbId;private UserAddress userAddress;private Instant lastSeen;public User(UserLastname lastname, UserFirstname firstname, UserEmail email, UserPublicId userPublicId, UserImageUrl imageUrl, Instant lastModifiedDate, Instant createdDate, Set<Authority> authorities, Long dbId, UserAddress userAddress, Instant lastSeen) {this.lastname = lastname;this.firstname = firstname;this.email = email;this.userPublicId = userPublicId;this.imageUrl = imageUrl;this.lastModifiedDate = lastModifiedDate;this.createdDate = createdDate;this.authorities = authorities;this.dbId = dbId;this.userAddress = userAddress;this.lastSeen = lastSeen;}
}

通过builder()使用，通过结尾的build()返回新对象

UserBuilder.email(user.getEmail().value()).firstName(user.getFirstname().value()).lastName(user.getLastname().value()).publicId(user.getUserPublicId().value()).authorities(RestAuthority.fromSet(user.getAuthorities())).build()

Rust实现（值传递）建造者模式

和直接链式调用相比，添加了一个build函数返回新对象

// 注意使用了Default，没有builder的值有默认值
#[derive(Serialize, Deserialize, Clone, Debug, Default)]
pub struct Customer {// uuiduser_id: String,// 用户名username: String,// 邮件email: String,// 密码password: String,// 头像avatar: Option<String>,// 验证码verify_code: Option<String>,// 收货地址receive_address: Vec<ReceiveAddress>,
}
// 建造(者结构体，包含一个需要构建的对象
#[derive(Default, Clone, Debug)]
pub struct CustomerBuilder {customer: Customer,
}
impl CustomerBuilder {pub fn new() -> Self {// 初始化默认值CustomerBuilder::default()}pub fn user_id(mut self, user_id: String) -> Self {self.customer.user_id = user_id;self}pub fn username(mut self, username: String) -> Self {self.customer.username = username;self}pub fn email(mut self, email: String) -> Self {self.customer.email = email;self}pub fn password(mut self, password: String) -> Self {self.customer.password = password;self}pub fn avatar(mut self, avatar: Option<String>) -> Self {self.customer.avatar = avatar;self}pub fn verify_code(mut self, verify_code: Option<String>) -> Self {self.customer.verify_code = verify_code;self}pub fn receive_address(mut self, receive_address: Vec<ReceiveAddress>) -> Self {self.customer.receive_address = receive_address;self}pub fn build(self) -> Customer {Customer {user_id: self.customer.user_id,username: self.customer.username,email: self.customer.email,password: self.customer.password,avatar: self.customer.avatar,verify_code: self.customer.verify_code,receive_address: self.customer.receive_address,}}
}

使用，没有建造的字段由于Default宏的存在会初始化默认值，这种用法和第二种链式调用方式相比每次创建新对象，对象无法修改，只能创建新对象，使用对象会消耗对象，适合创建值对象、响应DTO、Event（因为这些对象用完就会被Drop，创建后就不可变）

   let customer_builder = CustomerBuilder::new();let customer = customer_builder.clone().user_id("123".to_string()).username("张三".to_string()).email("<EMAIL>".to_string());let customer = customer.clone().avatar(Some("https://www.baidu.com".to_string()));let customer = customer.clone().build();print!("{:?}\n", customer);// Customer { user_id: "123", username: "张三", email: "<EMAIL>", password: "", avatar: Some("https://www.baidu.com"), verify_code: None, receive_address: [] }// 创建新对象let customer = customer_builder.clone().email("[e-mail]".to_string()).build();println!("{:?}", customer);// Customer { user_id: "", username: "", email: "[e-mail]", password: "", avatar: None, verify_code: None, receive_address: [] }

Rust实现（引用修改）建造者模式

如果不想消耗对象，可以将其字段都设置为&mut，使用clone()是为了返回的新对象是完全独立的副本

// 注意使用了Default，没有builder的值有默认值
#[derive(Serialize, Deserialize, Clone, Debug, Default)]
pub struct Customer {// uuiduser_id: String,// 用户名username: String,// 邮件email: String,// 密码password: String,// 头像avatar: Option<String>,// 验证码verify_code: Option<String>,// 收货地址receive_address: Vec<ReceiveAddress>,
}
// 建造(者结构体，包含一个需要构建的对象
#[derive(Default, Clone, Debug)]
pub struct CustomerBuilder {customer: Customer,
}
impl CustomerBuilder {pub fn new() -> Self {CustomerBuilder::default()}pub fn user_id(&mut self, user_id: String) -> &mut Self {self.customer.user_id = user_id;self}pub fn username(&mut self, username: String) -> &mut Self {self.customer.username = username;self}pub fn email(&mut self, email: String) -> &mut Self {self.customer.email = email;self}pub fn password(&mut self, password: String) -> &mut Self {self.customer.password = password;self}pub fn avatar(&mut self, avatar: Option<String>) -> &mut Self {self.customer.avatar = avatar;self}pub fn verify_code(&mut self, verify_code: Option<String>) -> &mut Self {self.customer.verify_code = verify_code;self}pub fn receive_address(&mut self, receive_address: Vec<ReceiveAddress>) -> &mut Self {self.customer.receive_address = receive_address;self}pub fn build(&self) -> Customer {Customer {user_id: self.customer.user_id.clone(),username: self.customer.username.clone(),email: self.customer.email.clone(),password: self.customer.password.clone(),avatar: self.customer.avatar.clone(),verify_code: self.customer.verify_code.clone(),receive_address: self.customer.receive_address.clone(),}}
}

使用，这里对象创建后不会消耗对象，可以通过.build()修改并返回新对象，适合创建领域模型如聚合对象

let mut binding = CustomerBuilder::new().clone();
let customer = binding.user_id("123".to_string()).username("张三".to_string()).email("<EMAIL>".to_string());
let customer = customer.avatar(Some("https://www.baidu.com".to_string()));
let customer = customer.build();
print!("{:?}\n", customer);
//Customer { user_id: "123", username: "张三", email: "<EMAIL>", password: "", avatar: Some("https://www.baidu.com"), verify_code: None, receive_address: [] }
// 修改原有对象
let customer = binding.email("[e-mail]".to_string()).build();
println!("{:?}", customer);
//Customer { user_id: "123", username: "张三", email: "[e-mail]", password: "", avatar: Some("https://www.baidu.com"), verify_code: None, receive_address: [] }