Introduction

When developing backend API services, DTOs are crucial for parameter validation and Swagger metadata generation. If DTOs can't be dynamically inferred, similar to type inference, then we still need to manually create them. As the business grows, complex relations between models make manually creating DTOs increasingly cumbersome

Vona ORM pioneered the ability to dynamically infer and generate DTOs, freeing our hands and significantly improving productivity. It can even be said that being able to dynamically infer and generate DTOs is a very important milestone in building a more elegant Node.js backend framework

DTO Tools

Vona ORM provides the following DTO Tools:

Name	Description
$Dto.get	Annotate the return result
$Dto.selectAndCount	Annotate the return result with paging
$Dto.query/DtoQueryBase	Annotate the query parameters
$Dto.queryPage/DtoQueryPageBase	Annotate the query parameters with paging
$Dto.create	Annotate the Create parameters
$Dto.update	Annotate the Update parameters
$Dto.aggregate	Annotate the return result of the aggregation operation
$Dto.group	Annotate the return result of the grouping operation

DTO Usage

The following uses the Order/Product model as an example to demonstrate how to perform query operations on the main-details models

1. Model Relations Definition

First, define a 1:n relation between the Order model and the Product model

@Model({
  entity: EntityOrder,
  relations: {
    products: $relation.hasMany(() => ModelProduct, 'orderId', {
      columns: ['id', 'name', 'price', 'quantity', 'amount'],
    }),
  },
})
class ModelOrder {}

2. Creating the API Endpoint

Create a Controller and Provide a findAll Method

class ControllerOrder {
  @Web.get('findAll')
  async findAll() {
    return this.scope.model.order.select({
      include: {
        products: true,
      },
    });
  }
}

3. Dynamically Inferring and Generating DTO

Since the result returned by this API is a main-details structure, we cannot simply use an EntityOrder array to annotate the return type. Instead, DTOs are used for dynamic inference and generation

+ import { $Dto } from 'vona-module-a-orm';

class ControllerOrder {
  @Web.get('findAll')
+ @Api.body(v.array($Dto.get(() => ModelOrder, { include: { products: true } })))
  async findAll() {
    return this.scope.model.order.select({
      include: {
        products: true,
      },
    });
  }
}

• @Api.body: Annotates the return result
• v.array: Annotates an array
• $Dto.get: Used for dynamic DTO inference and generation

The DTO generated by $Dto.get uses a main-details structure, which Swagger/OpenAPI is as follows:

4. Encapsulating the DTO

We can also create a new DTO class to encapsulate the $Dto.get code for use elsewhere

1. In VSCode, use the Vona Create/Dto context menu to create a DTO code skeleton:

@Dto()
export class DtoOrderResult {}

2. Encapsulate the DTO using inheritance:

+ import { $Dto } from 'vona-module-a-orm';

@Dto()
export class DtoOrderResult
+ extends $Dto.get(() => ModelOrder, { include: { products: true } }) {}

3. Now, let's refactor the previous code using DtoOrderResult:

class ControllerOrder {
  @Web.get('findAll')
+ @Api.body(v.array(DtoOrderResult))
+ async findAll(): Promise<DtoOrderResult[]> {
    return this.scope.model.order.select({
      include: {
        products: true,
      },
    });
  }
}

• Line 3: Directly annotating the type with v.array(DtoOrderResult)
• Line 4: The method return type is Promise<DtoOrderResult[]>