How to Override Price Selection Strategy

In this document, you’ll learn how to override Medusa’s price selection strategy to create a custom pricing strategy.

If you’re interested in learning what a price selection strategy is and how it works, check out this documentation instead.

1. Create Class

Create a TypeScript or JavaScript file in src/strategies of your Medusa backend project with a class that extends the AbstractPriceSelectionStrategy class:

src/strategies/price.ts

import { 
  AbstractPriceSelectionStrategy, 
  IPriceSelectionStrategy, 
  PriceSelectionContext, 
  PriceSelectionResult,
} from "@medusajs/medusa"

import { EntityManager } from "typeorm"

export default class MyStrategy extends 
  AbstractPriceSelectionStrategy {
    withTransaction(
      manager: EntityManager
    ): IPriceSelectionStrategy {
      if (!manager) {
        return this
      }

      return new MyStrategy()
    }

    async calculateVariantPrice(
      variant_id: string,
      context: PriceSelectionContext
    ): Promise<PriceSelectionResult> {
      // TODO
    }
}

You can use services or repositories in the strategy by adding them to the constructor and updating the parameters passed to the MyStrategy constructor in withTransaction. For example:

import { 
  AbstractPriceSelectionStrategy, 
  CustomerService, 
  IPriceSelectionStrategy, 
  PriceSelectionContext, 
  PriceSelectionResult, 
} from "@medusajs/medusa"

export default class MyStrategy extends 
  AbstractPriceSelectionStrategy {
    private customerService: CustomerService

    constructor({
      customerService,
    }) {
      super()
      this.customerService = customerService
    }

    withTransaction(
      manager: EntityManager
    ): IPriceSelectionStrategy {
      if (!manager) {
        return this
      }

      return new MyStrategy({
        customerService: this.customerService,
      })
    }
    // ...
}

---

2. Implement calculateVariantPrice

Implement the price selection strategy you want inside the calculateVariantPrice method.

This method accepts the variant ID as a first parameter and the context object as a second parameter.

This method must return an object having the following fields:

{
  originalPrice, // number | null
  calculatedPrice, // number | null
  prices // MoneyAmount[]
}

You can learn more about optional properties and the meaning behind every property here.

---

3. Run Build Command

In your terminal, run the build command to transpile the files in the src directory into the dist directory:

• npm
• Yarn
• pnpm

npm run build

yarn build

pnpm run build

---

Test it Out

Run your backend to test it out:

• npm
• Yarn
• pnpm

npx @medusajs/medusa-cli develop

npx @medusajs/medusa-cli develop

npx @medusajs/medusa-cli develop

Then, try out your strategy using any of the Products or Carts endpoints which include retrieving product variants and line items respectively. You should then see the prices in the response based on your implemented strategy.