Using Azure Functions to call REST API and save results in Azure Data Lake gen2

Question

I want to call a rest api and save the results as a csv or json file in Azure Data Lake Gen2. Based on what I have read Azure Functions is the way to go.

The webservice returns data like the following format:

"ID","ProductName","Company"
"1","Apples","Alfreds futterkiste"
"2","Oranges","Alfreds futterkiste"
"3","Bananas","Alfreds futterkiste"
"4","Salad","Alfreds futterkiste"
 ...next rows

I have written a console app in C# which at the moment outputs the data to a console. The webservice uses pagination and returns 1000 rows (determined by the &num-parameter with a max of 1000). After the first request i can use the &next-parameter to fetch the next 1000 rows based on ID. For instance the url

http://testWebservice123.com/Example.csv?auth=abc&number=1000&next=1000

will get me rows from ID 1001 to 2000. (the call of the API and the pagination in reality is a bit more complex and thus I cannot use for instance Azure Data Factory_v2 to do the load to Azure Data Lake - this is why I think i need Azure Functions - unless I have overlooked another servic??. So the following is just a demo to learn how to write to Azure Data Lake.)

I have the following C#:

static void Main(string[] args)
    {


        string startUrl = "http://testWebservice123.com/Example.csv?auth=abc&number=1000";
        string url = "";
        string deltaRequestParameter = "";
        string lastLine;
        int numberOfLines = 0;

        do
        {
            url = startUrl + deltaRequestParameter;
            WebClient myWebClient = new WebClient();

            using (Stream myStream = myWebClient.OpenRead(url))
            {

                using (StreamReader sr = new StreamReader(myStream))
                {
                    numberOfLines = 0;
                    while (!sr.EndOfStream)
                    {
                        var row = sr.ReadLine();
                        var values = row.Split(',');

                        //do whatever with the rows by now - i.e. write to console
                        Console.WriteLine(values[0] + " " + values[1]); 

                        lastLine = values[0].Replace("\"", ""); //last line in the loop - get the last ID.
                        numberOfLines++;
                        deltaRequestParameter = "&next=" + lastLine;
                    }

                }

            }
        } while (numberOfLines == 1001); //since the header is returned each time the number of rows will be 1001 until we get to the last request


    }

I want to write the data to a csv-file to the data-lake in the most effective way. How would I rewrite the above code to work in Azure Function and save to a csv in Azure data lake gen2?

Answer 1

Here are the steps which you need to do for achieving the result:

1) Create an azure function and trigger you can keep it HTTPTrigger/TimerTrigger, or as per your need.

2) I am assuming you have the code to call api in loop until it gives you desired result.

3) Once you have the Data in memory , you have to write following code to write it in Azure data lake.

Prerequisite for accessing ADLS using your c# code:

1) Register an app in Azure AD

Grant permission in data lake store

Below is the code for creating ADLS client.

// ADLS connection 
                var adlCreds = GetCreds_SPI_SecretKey(tenantId, ADL_TOKEN_AUDIENCE, serviceAppIDADLS, servicePrincipalSecretADLS);
                var adlsClient = AdlsClient.CreateClient(adlsName, adlCreds);



private static ServiceClientCredentials GetCreds_SPI_SecretKey(string tenant,Uri tokenAudience,string clientId,string secretKey)
        {
            SynchronizationContext.SetSynchronizationContext(new SynchronizationContext());
            var serviceSettings = ActiveDirectoryServiceSettings.Azure;
            serviceSettings.TokenAudience = tokenAudience;
            var creds = ApplicationTokenProvider.LoginSilentAsync(tenant,clientId,secretKey,serviceSettings).GetAwaiter().GetResult();
            return creds;
        }

Finally write the implementation to save the file in Azure data lake

 const string delim = ",";
        static string adlsInputPath = ConfigurationManager.AppSettings.Get("AdlsInputPath");

public static void ProcessUserProfile(this SampleProfile, AdlsClient adlsClient, string fileNameExtension = "")
        {
            using (MemoryStream memStreamProfile = new MemoryStream())
            {
                using (TextWriter textWriter = new StreamWriter(memStreamProfile))
                {
                    string profile;
                    string header = Helper.GetHeader(delim, Entities.FBEnitities.Profile);
                    string fileName = adlsInputPath + fileNameExtension + "/profile.csv";
                    adlsClient.DataLakeFileHandler(textWriter, header, fileName);
                    profile = socialProfile.UserID                                                
                                    + delim + socialProfile.Profile.First_Name
                                    + delim + socialProfile.Profile.Last_Name
                                    + delim + socialProfile.Profile.Name
                                    + delim + socialProfile.Profile.Age_Range_Min
                                    + delim + socialProfile.Profile.Age_Range_Max
                                    + delim + socialProfile.Profile.Birthday
                                   ;

                    textWriter.WriteLine(profile);
                    textWriter.Flush();
                    memStreamProfile.Flush();
                    adlsClient.DataLakeUpdateHandler(fileName, memStreamProfile);
                }
            }
        }

Hope it helps.