Azure API management policy: Unable to check if a parameter exists or not in request body

Question

I am having a control flow where I am specifying policy that will check if location property exists in request body, if exists I am sending the request with<send-request> here is my code:

<set-variable name="location-id" value="@((string)context.Request.Body.As<JObject>(preserveContent: true)["location"]["id"])" />                                                
<choose>
    <when condition="@(!string.IsNullOrEmpty(context.Request.Body.As<JObject>(true)["location"].Value<string>()))">     
        <send-request mode="new" timeout="20" response-variable-name="locationid" ignore-error="false">
            <set-url>@($"https://api.dev.com/external/location/location/{(string)context.Variables["location-id"]}")</set-url>
            <set-method>GET</set-method>
            <set-header name="Content-Type" exists-action="override">
                <value>application/json</value>
            </set-header>
            <set-header name="Authorization" exists-action="override">
            <value>@(context.Request.Headers.GetValueOrDefault("Authorization","scheme param"))</value>
            </set-header>
            <set-body>@{ var document = (JObject)context.Variables["newRequest"];
                            return document?.ToString();
                        }</set-body>
        </send-request>
    </when>
    <otherwise />
</choose>

Here is my request body:

{
  "id": 0,
  "policyList": [
    {
      "id": 4,
      "number": "string",
      "uri": "string"
    }
  ],
  "primaryPolicy": {
    "id": 23,
    "number": "string",
    "uri": "string"
  },
  "isLocationAmountRequired": true,
  "currency": 0,

  "location": {
    "id": 1,
    "number": "string",
    "postcode": "string",
    "name": "string",
    "uri": "string"
  },
  "modifiedOn": "string",
  "modifiedBy": {
    "adObjectId": "string",
    "adUserPrincipalName": "string",
    "adName": "string",
    "email": "string"
  }
}

But after doing this I should get a response but I am getting 500 internal server error

{
    "statusCode": 500,
    "message": "Internal server error",
    "activityId": "fa17a054-fbfb-477e-9637-276257808c65"
}

what should I do to solve this issue

Answer 1

Trace is returning following failure:

choose (10.095 ms)

{
    "messages": [
        {
            "message": "Expression evaluation failed.",
            "expression": "!string.IsNullOrEmpty(context.Request.Body.As<JObject>(true)[\"location\"].Value<string>())",
            "details": "Cannot cast Newtonsoft.Json.Linq.JObject to Newtonsoft.Json.Linq.JToken.\r\n   at Newtonsoft.Json.Linq.Extensions.Convert[T,U](T token)"
        },
        "Expression evaluation failed. Cannot cast Newtonsoft.Json.Linq.JObject to Newtonsoft.Json.Linq.JToken.\r\n   at Newtonsoft.Json.Linq.Extensions.Convert[T,U](T token)",
        "Cannot cast Newtonsoft.Json.Linq.JObject to Newtonsoft.Json.Linq.JToken."
    ]
}

1. If the location property is missing, the set-variable will fail before the choose condition. Please move this part into the choose condition:
   <set-variable name="location-id" value="@((string)context.Request.Body.As<JObject>(preserveContent: true)["location"]["id"])" />
2. Check your request for
   2.1 location is missing: context.Request.Body.As<JObject>(true)["location"] != null
   2.2 location is null: context.Request.Body.As<JObject>(true)["location"].Type != JTokenType.Null
   2.3 Complete when statement: <when condition="@(context.Request.Body.As<JObject>(true)["location"] != null && context.Request.Body.As<JObject>(true)["location"].Type != JTokenType.Null)">

3.In the end, the missing variable newRequest has to to be added in the policy:

set-body (0.589 ms)

{
    "messages": [
        {
            "message": "Expression evaluation failed.",
            "expression": " var document = (JObject)context.Variables[\"newRequest\"];\n                                return document?.ToString();\n                                ",
            "details": "The given key was not present in the dictionary.\r\n   at System.ThrowHelper.ThrowKeyNotFoundException()\r\n   at System.Collections.Generic.Dictionary`2.get_Item(TKey key)"
        },
        "Expression evaluation failed. The given key was not present in the dictionary.\r\n   at System.ThrowHelper.ThrowKeyNotFoundException()\r\n   at System.Collections.Generic.Dictionary`2.get_Item(TKey key)",
        "The given key was not present in the dictionary."
    ]
}

Complete policy:

<policies>
    <inbound>
        <base />
        <choose>
            <when condition="@(context.Request.Body.As<JObject>(true)["location"] != null && context.Request.Body.As<JObject>(true)["location"].Type != JTokenType.Null)">
                <set-variable name="location-id" value="@((string)context.Request.Body.As<JObject>(preserveContent: true)["location"]["id"])" />
                <send-request mode="new" timeout="20" response-variable-name="locationid" ignore-error="false">
                    <set-url>@($"https://api.dev.com/external/location/location/{(string)context.Variables["location-id"]}")</set-url>
                    <set-method>GET</set-method>
                    <set-header name="Content-Type" exists-action="override">
                        <value>application/json</value>
                    </set-header>
                    <set-header name="Authorization" exists-action="override">
                        <value>@(context.Request.Headers.GetValueOrDefault("Authorization","scheme param"))</value>
                    </set-header>
                    <!-- newRequest is not defined in policy which will cause an error -->
                    <set-body>@{ var document = (JObject)context.Variables["newRequest"];
                                return document?.ToString();
                                }</set-body>
                </send-request>
            </when>
            <otherwise />
        </choose>
    </inbound>
    <backend>
        <base />
    </backend>
    <outbound>
        <base />
    </outbound>
    <on-error>
        <base />
    </on-error>
</policies>