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Services in Medusa encapsulate business logic and data access for specific domains. They extend the MedusaService base class and use decorators for transaction management and event handling.

​
What is a Service?

A Medusa service:
  • Extends MedusaService to get automatic CRUD methods
  • Manages data access for one or more entities
  • Uses decorators for cross-cutting concerns (transactions, events)
  • Can be injected into workflows, API routes, and other services
  • Provides type-safe DTOs for inputs and outputs

​
Creating a Service

1

Define Your Entity

First, create your data model:
src/modules/brand/models/brand.ts
import { Entity, Property, OneToMany } from "@mikro-orm/core"
import { BaseEntity } from "@medusajs/framework/utils"

@Entity()
export class Brand extends BaseEntity {
  @Property()
  name: string

  @Property({ nullable: true })
  description?: string

  @Property({ nullable: true })
  logo_url?: string

  @Property({ default: true })
  is_active: boolean = true
}
2

Create the Service Class

Extend MedusaService with your entity configuration:
src/modules/brand/services/brand-module-service.ts
import {
  Context,
  DAL,
  InternalModuleDeclaration,
} from "@medusajs/framework/types"
import {
  InjectManager,
  InjectTransactionManager,
  MedusaContext,
  MedusaService,
  ModulesSdkTypes,
} from "@medusajs/framework/utils"
import { Brand } from "../models"
import { BrandDTO, CreateBrandDTO } from "../types"

type InjectedDependencies = {
  baseRepository: DAL.RepositoryService
  brandService: ModulesSdkTypes.IMedusaInternalService<Brand>
}

export default class BrandModuleService extends MedusaService<{
  Brand: {
    dto: BrandDTO
  }
}>({
  Brand,
}) {
  protected baseRepository_: DAL.RepositoryService
  protected brandService_: ModulesSdkTypes.IMedusaInternalService<Brand>

  constructor(
    { baseRepository, brandService }: InjectedDependencies,
    protected readonly moduleDeclaration: InternalModuleDeclaration
  ) {
    super(...arguments)
    this.baseRepository_ = baseRepository
    this.brandService_ = brandService
  }
}
The service automatically gets these methods:
  • createBrands(data: CreateBrandDTO[]): Promise<BrandDTO[]>
  • updateBrands(data: UpdateBrandDTO[]): Promise<BrandDTO[]>
  • listBrands(filters?, config?): Promise<BrandDTO[]>
  • listAndCountBrands(filters?, config?): Promise<[BrandDTO[], number]>
  • retrieveBrand(id, config?): Promise<BrandDTO>
  • deleteBrands(ids: string[]): Promise<void>
  • softDeleteBrands(ids: string[]): Promise<void>
  • restoreBrands(ids: string[]): Promise<void>
3

Add Custom Methods

Implement custom business logic:
export default class BrandModuleService extends MedusaService<{
  Brand: { dto: BrandDTO }
}>({
  Brand,
}) {
  // ... constructor ...

  @InjectManager()
  async findByName(
    name: string,
    @MedusaContext() sharedContext: Context = {}
  ): Promise<BrandDTO | null> {
    const [brand] = await this.brandService_.list(
      { name },
      { take: 1 },
      sharedContext
    )
    return brand ? await this.baseRepository_.serialize(brand) : null
  }

  @InjectManager()
  async listActiveBrands(
    @MedusaContext() sharedContext: Context = {}
  ): Promise<BrandDTO[]> {
    const brands = await this.brandService_.list(
      { is_active: true },
      {},
      sharedContext
    )
    return await this.baseRepository_.serialize(brands)
  }
}

​
Service Decorators

Decorators provide cross-cutting functionality for your service methods.

​
@InjectManager

Injects the entity manager for database operations. Use on public methods: 
@InjectManager()
async createBrand(
  data: CreateBrandDTO,
  @MedusaContext() sharedContext: Context = {}
): Promise<BrandDTO> {
  const [brand] = await this.createBrands([data], sharedContext)
  return brand
}

​
@InjectTransactionManager

Injects a transactional entity manager. Use on protected methods that modify data: 
@InjectTransactionManager()
protected async updateBrandStatus_(
  id: string,
  isActive: boolean,
  @MedusaContext() sharedContext: Context = {}
): Promise<Brand> {
  const brand = await this.brandService_.retrieve(id, {}, sharedContext)
  brand.is_active = isActive
  await this.brandService_.update([brand], sharedContext)
  return brand
}

​
@MedusaContext

Marks the context parameter for transaction and manager injection: 
async listBrands(
  filters: FilterableBrandProps = {},
  config: FindConfig<BrandDTO> = {},
  @MedusaContext() sharedContext: Context = {}
): Promise<BrandDTO[]> {
  return await this.brandService_.list(filters, config, sharedContext)
}

​
@EmitEvents

Automatically emits events after method execution: 
import { EmitEvents } from "@medusajs/framework/utils"

@InjectManager()
@EmitEvents()
async activateBrand(
  id: string,
  @MedusaContext() sharedContext: Context = {}
): Promise<BrandDTO> {
  const brand = await this.updateBrandStatus_(id, true, sharedContext)
  
  // Event automatically emitted
  this.aggregatedEvents({
    action: "activated",
    object: "brand",
    data: { id },
    context: sharedContext,
  })
  
  return await this.baseRepository_.serialize(brand)
}

​
Complete Service Example

Here’s a full service implementation with custom logic:
src/modules/brand/services/brand-module-service.ts
import {
  Context,
  DAL,
  FilterableProductProps,
  FindConfig,
  InternalModuleDeclaration,
} from "@medusajs/framework/types"
import {
  EmitEvents,
  InjectManager,
  InjectTransactionManager,
  MedusaContext,
  MedusaError,
  MedusaService,
  ModulesSdkTypes,
} from "@medusajs/framework/utils"
import { Brand } from "../models"
import { BrandDTO, CreateBrandDTO, UpdateBrandDTO } from "../types"

type InjectedDependencies = {
  baseRepository: DAL.RepositoryService
  brandService: ModulesSdkTypes.IMedusaInternalService<Brand>
}

export default class BrandModuleService extends MedusaService<{
  Brand: {
    dto: BrandDTO
  }
}>({
  Brand,
}) {
  protected baseRepository_: DAL.RepositoryService
  protected brandService_: ModulesSdkTypes.IMedusaInternalService<Brand>

  constructor(
    { baseRepository, brandService }: InjectedDependencies,
    protected readonly moduleDeclaration: InternalModuleDeclaration
  ) {
    super(...arguments)
    this.baseRepository_ = baseRepository
    this.brandService_ = brandService
  }

  // Custom retrieval methods
  @InjectManager()
  async findByName(
    name: string,
    @MedusaContext() sharedContext: Context = {}
  ): Promise<BrandDTO | null> {
    const [brand] = await this.brandService_.list(
      { name },
      { take: 1 },
      sharedContext
    )
    return brand ? await this.baseRepository_.serialize(brand) : null
  }

  @InjectManager()
  async listActiveBrands(
    filters: FilterableProductProps = {},
    config: FindConfig<BrandDTO> = {},
    @MedusaContext() sharedContext: Context = {}
  ): Promise<BrandDTO[]> {
    const brands = await this.brandService_.list(
      { ...filters, is_active: true },
      config,
      sharedContext
    )
    return await this.baseRepository_.serialize(brands)
  }

  // Custom business logic
  @InjectManager()
  @EmitEvents()
  async activateBrand(
    id: string,
    @MedusaContext() sharedContext: Context = {}
  ): Promise<BrandDTO> {
    const brand = await this.updateBrandStatus_(id, true, sharedContext)

    this.aggregatedEvents({
      action: "activated",
      object: "brand",
      data: { id },
      context: sharedContext,
    })

    return await this.baseRepository_.serialize(brand)
  }

  @InjectManager()
  @EmitEvents()
  async deactivateBrand(
    id: string,
    @MedusaContext() sharedContext: Context = {}
  ): Promise<BrandDTO> {
    const brand = await this.updateBrandStatus_(id, false, sharedContext)

    this.aggregatedEvents({
      action: "deactivated",
      object: "brand",
      data: { id },
      context: sharedContext,
    })

    return await this.baseRepository_.serialize(brand)
  }

  // Protected helper methods
  @InjectTransactionManager()
  protected async updateBrandStatus_(
    id: string,
    isActive: boolean,
    @MedusaContext() sharedContext: Context = {}
  ): Promise<Brand> {
    const brand = await this.brandService_.retrieve(id, {}, sharedContext)

    if (!brand) {
      throw new MedusaError(
        MedusaError.Types.NOT_FOUND,
        `Brand with id: ${id} was not found`
      )
    }

    brand.is_active = isActive
    const [updated] = await this.brandService_.update([brand], sharedContext)
    return updated
  }
}

​
Working with Relationships

Define relationships in your entities:
src/modules/brand/models/brand.ts
import { Entity, Property, OneToMany, Collection } from "@mikro-orm/core"
import { BaseEntity } from "@medusajs/framework/utils"

@Entity()
export class Brand extends BaseEntity {
  @Property()
  name: string

  @OneToMany(() => Product, (product) => product.brand)
  products = new Collection<Product>(this)
}
src/modules/brand/models/product.ts
import { Entity, ManyToOne } from "@mikro-orm/core"

@Entity()
export class Product extends BaseEntity {
  @ManyToOne(() => Brand)
  brand: Brand
}
Query with relationships: 
@InjectManager()
async getBrandWithProducts(
  id: string,
  @MedusaContext() sharedContext: Context = {}
): Promise<BrandDTO> {
  const brand = await this.brandService_.retrieve(
    id,
    {
      relations: ["products"],
    },
    sharedContext
  )
  return await this.baseRepository_.serialize(brand)
}

​
Error Handling

Use MedusaError for consistent error handling: 
import { MedusaError } from "@medusajs/framework/utils"

@InjectManager()
async retrieveBrandByName(
  name: string,
  @MedusaContext() sharedContext: Context = {}
): Promise<BrandDTO> {
  const brand = await this.findByName(name, sharedContext)

  if (!brand) {
    throw new MedusaError(
      MedusaError.Types.NOT_FOUND,
      `Brand with name "${name}" was not found`
    )
  }

  return brand
}
Common error types:
  • MedusaError.Types.NOT_FOUND - Resource not found
  • MedusaError.Types.INVALID_DATA - Invalid input data
  • MedusaError.Types.NOT_ALLOWED - Operation not permitted
  • MedusaError.Types.DUPLICATE_ERROR - Duplicate entry

​
Emitting Events

Use aggregatedEvents to emit domain events: 
this.aggregatedEvents({
  action: "created",
  object: "brand",
  data: { id: brand.id },
  context: sharedContext,
})
The framework automatically formats and emits these events through the event bus.

​
Best Practices

  • Use @InjectManager() for public methods
  • Use @InjectTransactionManager() for protected methods that modify data
  • Always include @MedusaContext() parameter for database operations
  • Serialize entities before returning them: this.baseRepository_.serialize()
  • Use the auto-generated CRUD methods instead of reimplementing them
  • Throw MedusaError for error handling
  • Emit events using aggregatedEvents() for important state changes
  • Keep business logic in services, not in API routes
  • Use protected methods (ending with _) for internal operations

​
Next Steps

Create Workflows

Compose services into workflows

Create Custom Modules

Package services into modules

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