How do I specify a policy so that Azure API Management creates a different response cache for each combination of query parameters?

Question

How do I specify a policy so that Azure API Management creates a different response cache for each combination of query parameters?

Suppose I have an endpoint /my-endpoint that takes 2 query parameters (item_id and language).

I want API Management to make a different cache for each combination of my query parameter values.

For example, I want the following requests to store different cache values for the responses:

/my-endpoint?item_id=4&language=en
/my-endpoint?item_id=4&language=nl
/my-endpoint?item_id=2&language=en
/my-endpoint?item_itd=2&language=nl

How do I do this?

In particular, do both of the following APIM policies (APIM Policy 1 and APIM Policy 2) work? Or is there a difference in how Azure API Management response caching works when I use a single tag with values separated by commas (see APIM Policy 1), or when I use multiple tags, each with a different value (see APIM Policy 2)?

APIM Policy 1

<policies>
        <inbound>
            <base />
            <cache-lookup vary-by-developer="false" vary-by-developer-groups="false" allow-private-response-caching="false" must-revalidate="false" downstream-caching-type="none">
                <vary-by-query-parameter>item_id;language</vary-by-query-parameter>
            </cache-lookup>
        </inbound>
        <backend>
            <base />
        </backend>
        <outbound>
            <base />
            <cache-store duration="3600" />
        </outbound>
        <on-error>
            <base />
        </on-error>
</policies>

APIM Policy 2

<policies>
        <inbound>
            <base />
            <cache-lookup vary-by-developer="false" vary-by-developer-groups="false" allow-private-response-caching="false" must-revalidate="false" downstream-caching-type="none">
                <vary-by-query-parameter>item_id</vary-by-query-parameter>
                <vary-by-query-parameter>language</vary-by-query-parameter>
            </cache-lookup>
        </inbound>
        <backend>
            <base />
        </backend>
        <outbound>
            <base />
            <cache-store duration="3600" />
        </outbound>
        <on-error>
            <base />
        </on-error>
</policies>

Answer 1

If you don't get the "vary-by-query-parameter" to work, you could do something like this:

<cache-store-value key="@("my-variable-" + context.Request.MatchedParameters.GetValueOrDefault("item_id","")) + "-" + context.Request.MatchedParameters.GetValueOrDefault("language",""))" value="@(context.Response.Body.As<String>(true))" duration="3600" />

In this way you combine your parameters to get unique cache variabel names.
Given your case above you will have 4 different cache variables:

my-variable-4-en
my-variable-4-nl
my-variable-2-en
my-variable-2-nl

They will all contain different response bodies.