Azure API Management Policy – Asynchronous API as Synchronous API

Below is the link to reference/examples of using Azure API management policy

There’s an example there on how to Mask Asynchronous calls as Synchronous API however for my requirement it’s not enough.

The target API behaves as follow:

  1. All operations are POST and asynchronous.
  2. To get the results of any operation a second API needs to be called and it’s expecting the transaction id.
  3. API expects a payload in command manner (args parameter) instead of proper JSON name/value pair.

Requirement: API should return the results in synchronous manner.

Solution:

API Callout Policy in API Management.

Steps: 

  1. Create a GET operation and via policy rewrite the operation to POST
  2. Create a JSON transformation logic in the inbound policy and execute the backend API.
  3. Create a JSON transformation logic in outbound policy and add a retry policy to execute the second API  that returns the result passing the transaction id from #2
  4. Return the results from second API.

Policy Code:

<policies>
<inbound>
<base />
<set-header name="Content-Type" exists-action="override">
<value>application/json</value>
</set-header>
<!-- Save authorization data to variable, to be used in outbound status request -->
<set-variable name="authorization" value="@(context.Request.Headers.GetValueOrDefault("Authorization"))" />
<!-- 
Construct the payload
-->
<set-body>@{
var paramFromRequest = Uri.UnescapeDataString(context.Request.OriginalUrl.Query.GetValueOrDefault("paramFromRequest"));
JObject transBody = new JObject();
transBody.Add("source", 
     new JObject
     {
         {"someproperty", "fixvalue"},
         {"someproperty2", "fixvalue2"},
     });

//Add all json properties as arg
transBody.Add("args", JToken.FromObject(new[] 
{ 
      paramFromRequest
}));
return transBody.ToString();
}</set-body>
<trace source="debug">@(context.Request.Body.As<string>(true))</trace>
<!--Remove additional query string -->
<set-query-parameter name="paramFromRequest" exists-action="delete" />
<set-method>POST</set-method>
<rewrite-uri template="{{FIRSTBACKENDAPI_URL}}" />
</inbound>
<backend>
<base />
</backend>
<outbound>
<base />
<!-- Get the Key from response -->
<set-variable name="jsonPayload" value="@{ 
JObject inBody = context.Response.Body.As<JObject>();
var transactionId= inBody["transactionId"].ToString(); 
string jsonString = "{\"transactionId\":\"_transactionId\" }";
var json = jsonString.Replace("_transactionId", transactionId);
return json;
}" />
<retry condition="@( Convert.ToBoolean(context.Variables.GetValueOrDefault<JObject>("status")["{{PROPERTYNAME IN JSON OBJECT RESPONSE}}"]))" count="10" interval="1">
<!-- Call Status API to get the results-->
<send-request mode="new" response-variable-name="var" ignore-error="false">
<set-url>@{ 
var url = context.Api.ServiceUrl+ "{{SECONDBACKENDAPI_URL}}";
return url;
}</set-url>
<set-method>POST</set-method>
<set-header name="Authorization" exists-action="override">
<value>@(context.Variables.GetValueOrDefault<string>("authorization"))</value>
</set-header>
<set-header name="Content-Type" exists-action="override">
<value>application/json</value>
</set-header>
<set-body template="none">@(context.Variables.GetValueOrDefault<string>("jsonPayload"))</set-body>
</send-request>
<set-variable name="results" value="@(((IResponse)context.Variables["var"]).Body.As<JObject>())" />
</retry>
<return-response>
<set-body template="none">@((context.Variables.GetValueOrDefault<JObject>("results")["{{PROPERTYNAME IN JSON OBJECT THAT CONTAINS THE RESULT}}"].ToString()))</set-body>
</return-response>
</outbound>
<on-error>
<base />
</on-error>
</policies>

 

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Querying Azure SQL Database using Azure Functions 2.0 to return JSON data

The guide below shows how you can easily query Azure SQL Database using Azure Functions.

I have to admit, I have to do multiple google search and combine it for a working solution.

Challenges:

  1. How to get SQL connectionString from Azure Function settings. https://docs.microsoft.com/en-us/azure/azure-functions/functions-scenario-database-table-cleanup
  2. How to convert the sql results to JSON.  https://stackoverflow.com/questions/5083709/convert-from-sqldatareader-to-json

Steps:

    • 1. Create a new Function with HTTP trigger
    • 2. Add a new file called serialize.csx with following contents below. This will convert the SQL rows to a JSON like data.
using System.Text;
using System.Data;
using System.Linq;
using System.Configuration;
using System.Data.SqlClient;
using System.Collections.Generic;
using System.Collections;
public static IEnumerable<Dictionary<string, object>> Serialize(SqlDataReader reader)
{
var results = new List<Dictionary<string, object>>();
var cols = new List<string>();
for (var i = 0; i < reader.FieldCount; i++)
{
var colName = reader.GetName(i);
var camelCaseName = Char.ToLowerInvariant(colName[0]) + colName.Substring(1);
cols.Add(camelCaseName);
}

while (reader.Read())
results.Add(SerializeRow(cols, reader));

return results;
}
private static Dictionary<string, object> SerializeRow(IEnumerable<string> cols,
SqlDataReader reader) {
var result = new Dictionary<string, object>();
foreach (var col in cols)
result.Add(col, reader[col]);
return result;
}

 

3. In the run.csx, paste the following code. This will query the Azure SQL database and returns the data.

#r "Newtonsoft.Json"
#load "serialize.csx"

using System.Net;

using Microsoft.AspNetCore.Mvc;

using Microsoft.Extensions.Primitives;

using Newtonsoft.Json;

using System.Text;

using System.Data;

using System.Linq;

using System.Configuration;

using System.Data.SqlClient;

using System.Collections.Generic;

public static async Task<HttpResponseMessage> Run(HttpRequest req, ILogger log)

{

log.LogInformation("C# HTTP trigger function processed a request.");

string name = req.Query["name"];

string json =" ";

try

{

var str = Environment.GetEnvironmentVariable("<ConnectionStringName in appSettings>");




using(SqlConnection conn =new SqlConnection(str))

{

using(SqlCommand cmd =new SqlCommand())

{

SqlDataReader dataReader;

cmd.CommandText = "<SQL QUERY HERE>";

cmd.CommandType = CommandType.Text;

cmd.Connection = conn;

conn.Open();

dataReader = cmd.ExecuteReader();

var r = Serialize(dataReader);

json = JsonConvert.SerializeObject(r, Formatting.Indented);

}

}

}

catch(SqlException sqlex)

{

log.LogInformation(sqlex.Message);

log.LogInformation(sqlex.ToString());

returnnew HttpResponseMessage(HttpStatusCode.BadRequest)

{

Content = new StringContent(JsonConvert.SerializeObject($"The following SqlException happened: {sqlex.Message}"), Encoding.UTF8, "application/json")

};

}

catch(Exception ex)

{

log.LogInformation(ex.Message);

log.LogInformation(ex.ToString());

returnnew HttpResponseMessage(HttpStatusCode.BadRequest)

{

Content = new StringContent(JsonConvert.SerializeObject($"The following SqlException happened: {ex.Message}"), Encoding.UTF8, "application/json")

};

}

returnnew HttpResponseMessage(HttpStatusCode.OK)

{

Content = new StringContent(json, Encoding.UTF8, "application/json")

};

}
This shows how you can easily query the Azure SQL Database and return the data JSON in few minutes.
Perhaps next steps is to deploy this Azure Function into API management.