medusa-store/www/apps/docs/content/references/medusa/interfaces/medusa.IPriceSelectionStrategy.mdx

---
displayed_sidebar: homepage
---

import ParameterTypes from "@site/src/components/ParameterTypes"

# IPriceSelectionStrategy

## Overview

The price selection strategy retrieves the best price for a product variant for a specific context such as selected region, taxes applied,
the quantity in cart, and more.

Medusa provides a default price selection strategy, but you can override it. A price selecion strategy is a TypeScript or JavaScript file in the `src/strategies` directory of your Medusa backend project. It exports a class that extends the `AbstractPriceSelectionStrategy` class.

For example:

```ts title="src/strategies/price.ts"
import {
  AbstractPriceSelectionStrategy,
  PriceSelectionContext,
  PriceSelectionResult,
} from "@medusajs/medusa"

export default class MyStrategy extends
  AbstractPriceSelectionStrategy {

  async calculateVariantPrice(
    data: {
      variantId: string;
      quantity?: number
    }[],
    context: PriceSelectionContext
  ): Promise<Map<string, PriceSelectionResult>> {
    throw new Error("Method not implemented.")
  }
}
```

---

## Methods

### calculateVariantPrice

This method retrieves one or more product variants' prices. It's used when retrieving product variants or their associated line items.
It's also used when retrieving other entities that product variants and line items belong to, such as products and carts respectively.

#### Example

For example, here's a snippet of how the price selection strategy is implemented in the Medusa backend:

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

type InjectedDependencies = {
  customerService: CustomerService
}

export default class MyStrategy extends
  AbstractPriceSelectionStrategy {

  async calculateVariantPrice(
    data: {
      variantId: string
      quantity?: number
    }[],
    context: PriceSelectionContext
  ): Promise<Map<string, PriceSelectionResult>> {
    const dataMap = new Map(data.map((d) => [d.variantId, d]))

    const cacheKeysMap = new Map(
      data.map(({ variantId, quantity }) => [
        variantId,
        this.getCacheKey(variantId, { ...context, quantity }),
      ])
    )

    const nonCachedData: {
      variantId: string
      quantity?: number
    }[] = []

    const variantPricesMap = new Map<string, PriceSelectionResult>()

    if (!context.ignore_cache) {
      const cacheHits = await promiseAll(
        [...cacheKeysMap].map(async ([, cacheKey]) => {
          return await this.cacheService_.get<PriceSelectionResult>(cacheKey)
        })
      )

      if (!cacheHits.length) {
        nonCachedData.push(...dataMap.values())
      }

      for (const [index, cacheHit] of cacheHits.entries()) {
        const variantId = data[index].variantId
        if (cacheHit) {
          variantPricesMap.set(variantId, cacheHit)
          continue
        }

        nonCachedData.push(dataMap.get(variantId)!)
      }
    } else {
      nonCachedData.push(...dataMap.values())
    }

    let results: Map<string, PriceSelectionResult> = new Map()

    if (
      this.featureFlagRouter_.isFeatureEnabled(
        TaxInclusivePricingFeatureFlag.key
      )
    ) {
      results = await this.calculateVariantPrice_new(nonCachedData, context)
    } else {
      results = await this.calculateVariantPrice_old(nonCachedData, context)
    }

    await promiseAll(
      [...results].map(async ([variantId, prices]) => {
        variantPricesMap.set(variantId, prices)
        if (!context.ignore_cache) {
          await this.cacheService_.set(cacheKeysMap.get(variantId)!, prices)
        }
      })
    )

    return variantPricesMap
  }

  // ...
}
```

#### Parameters

<ParameterTypes parameters={[{"name":"data","type":"`object`[]","description":"The necessary data to perform the price selection for each variant ID.","optional":false,"defaultValue":"","expandable":false,"children":[{"name":"variantId","type":"`string`","description":"The ID of the variant to retrieve its prices.","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"quantity","type":"`number`","description":"The variant's quantity in the cart, if available.","optional":true,"defaultValue":"","expandable":false,"children":[]}]},{"name":"context","type":"[PriceSelectionContext](medusa.PriceSelectionContext.mdx)","description":"The context of the price selection.","optional":false,"defaultValue":"","expandable":false,"children":[{"name":"cart_id","type":"`string`","description":"The cart's ID. This is used when the prices are being retrieved for the variant of a line item,\nas it is used to determine the current region and currency code of the context.","optional":true,"defaultValue":"","expandable":false,"children":[]},{"name":"customer_id","type":"`string`","description":"The ID of the customer viewing the variant.","optional":true,"defaultValue":"","expandable":false,"children":[]},{"name":"region_id","type":"`string`","description":"The region's ID.","optional":true,"defaultValue":"","expandable":false,"children":[]},{"name":"quantity","type":"`number`","description":"The quantity of the item in the cart. This is used to filter out price lists that have\n`min_quantity` or `max_quantity` conditions set.","optional":true,"defaultValue":"","expandable":false,"children":[]},{"name":"currency_code","type":"`string`","description":"The currency code the customer is using.","optional":true,"defaultValue":"","expandable":false,"children":[]},{"name":"include_discount_prices","type":"`boolean`","description":"Whether the price list's prices should be retrieved or not.","optional":true,"defaultValue":"","expandable":false,"children":[]},{"name":"tax_rates","type":"[TaxServiceRate](../types/medusa.TaxServiceRate.mdx)[]","description":"The tax rates to be applied. This is only used for\n[Tax-Inclusive Pricing](https://docs.medusajs.com/modules/taxes/inclusive-pricing).","optional":true,"defaultValue":"","expandable":false,"children":[]},{"name":"ignore_cache","type":"`boolean`","description":"Whether to calculate the prices even if the value of an earlier price calculation\nis available in the cache.","optional":true,"defaultValue":"","expandable":false,"children":[]}]}]} expandUrl="https://docs.medusajs.com/development/entities/repositories#retrieving-a-list-of-records" sectionTitle="calculateVariantPrice"/>

#### Returns

<ParameterTypes parameters={[{"name":"Promise","type":"Promise&#60;Map&#60;string, [PriceSelectionResult](medusa.PriceSelectionResult.mdx)&#62;&#62;","optional":false,"defaultValue":"","description":"A map, each key is an ID of a variant, and its value is an object holding the price selection result.","expandable":false,"children":[{"name":"Map","type":"Map&#60;string, [PriceSelectionResult](medusa.PriceSelectionResult.mdx)&#62;","optional":false,"defaultValue":"","description":"","expandable":false,"children":[]}]}]} expandUrl="https://docs.medusajs.com/development/entities/repositories#retrieving-a-list-of-records" sectionTitle="calculateVariantPrice"/>

### onVariantsPricesUpdate

This method is called when prices of product variants have changed.
You can use it to invalidate prices stored in the cache.

#### Example

For example, this is how this method is implemented in the Medusa backend's default
price selection strategy:

```ts
import {
  AbstractPriceSelectionStrategy,
  CustomerService,
} from "@medusajs/medusa"
import { promiseAll } from "@medusajs/utils"

type InjectedDependencies = {
  customerService: CustomerService
}

export default class MyStrategy extends
  AbstractPriceSelectionStrategy {

  public async onVariantsPricesUpdate(variantIds: string[]): Promise<void> {
    await promiseAll(
      variantIds.map(
        async (id: string) => await this.cacheService_.invalidate(`ps:${id}:*`)
      )
    )
  }

  // ...
}
```

:::note

Learn more about the cache service in [this documentation](https://docs.medusajs.com/development/cache/overview).

:::

#### Parameters

<ParameterTypes parameters={[{"name":"variantIds","type":"`string`[]","description":"The IDs of the updated variants.","optional":false,"defaultValue":"","expandable":false,"children":[]}]} expandUrl="https://docs.medusajs.com/development/entities/repositories#retrieving-a-list-of-records" sectionTitle="onVariantsPricesUpdate"/>

#### Returns

<ParameterTypes parameters={[{"name":"Promise","type":"Promise&#60;void&#62;","optional":false,"defaultValue":"","description":"Resolves after any necessary actions are performed.","expandable":false,"children":[]}]} expandUrl="https://docs.medusajs.com/development/entities/repositories#retrieving-a-list-of-records" sectionTitle="onVariantsPricesUpdate"/>

### withTransaction

#### Parameters

<ParameterTypes parameters={[{"name":"transactionManager","type":"`EntityManager`","description":"","optional":true,"defaultValue":"","expandable":false,"children":[]}]} expandUrl="https://docs.medusajs.com/development/entities/repositories#retrieving-a-list-of-records" sectionTitle="withTransaction"/>

#### Returns

<ParameterTypes parameters={[{"name":"this","type":"`this`","optional":false,"defaultValue":"","description":"","expandable":false,"children":[]}]} expandUrl="https://docs.medusajs.com/development/entities/repositories#retrieving-a-list-of-records" sectionTitle="withTransaction"/>