Azure function with a connection OPenAsync generates an exception

Question

Azure function with a connection OPenAsync generates an exception

Patrick M 0

Greetings Community,

The intent of my Azure C# function consists of accessing a Database hosted by a serverless Azure resource. With the use of the logger, I found out that it fails on the instruction

await connection.OpenAsync();

An exception is generated even though connection is not null. The following are few lines of StackTrace output:

2026-02-24T00:08:05 [Error] Exception Error fetching Message: Object reference not set to an instance of an object.

2026-02-24T00:08:05 [Error] Exception Error fetching Source: Microsoft.Data.SqlClient

2026-02-24T00:08:05 [Error] Exception Error fetching data: System.Collections.ListDictionaryInternal

2026-02-24T00:08:05 [Error] Exception Error fetching HelpLink:

2026-02-24T00:08:05 [Error] Exception Error fetching HResult: -2147467261

2026-02-24T00:08:05 [Error] Exception Error fetching TargetSite: System.Object LocalMachineRegistryValue(System.String, System.String)

This is my connection string:

Server=tcp:ucserver1.database.windows.net,1433;Database=Mydatabse;Persist Security Info=False;User ID=Myadmin;Password=MyPassword;MultipleActiveResultSets=False;Encrypt=True;TrustServerCertificate=False;Connection Timeout=60;ConnectRetryCount=2;ConnectRetryInterval=5

Regards,

Patrick M.

Praveen Kumar Gudipudi 1,880 Reputation points Microsoft External Staff Moderator

2026-02-24T09:01:49.02+00:00
Hello Patrick M,

it’s either firewall or missing App Setting in Azure.

Please provide below required details:

How you're reading the connection string

Your Function runtime (.NET version)

Hosting plan (Consumption / Premium / Dedicated)

Patrick M 0

Hi Praveen,

Thanks for your quick response. I forgot to tell that the performed is not local, but from the published function in Azure. Please, find below the information you requested:

1- How you're reading the connection string

     Answer: var connStr = Environment.GetEnvironmentVariable("SQL_CONNECTION_STRING");
```2- Your Function runtime (.NET version)

```yaml
     Answer: Curiously, the Operating System after publishing is Linux, even though I've selected winx64 from the publish properties in Visual Studio.
```3- Hosting plan (Consumption / Premium / Dedicated)           Answer: Flex consumption

4- My code

    private ILogger _logger = loggerFactory.CreateLogger<GetSimDataUsageInfo>();

    [Function("GetDataUsage")]

    static public async Task<IActionResult> Run(

        [HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = null)] HttpRequestData req,

        FunctionContext executionContext)

    {

        var logger = executionContext.GetLogger("GetSimUsageData");

        List<MyData> results = [];

        var connStr = Environment.GetEnvironmentVariable("SQL_CONNECTION_STRING");

        var API_PASSWORD = Environment.GetEnvironmentVariable("API_PASSWORD");

        var API_EMAIL = Environment.GetEnvironmentVariable("API_EMAIL");

        string token;

        Task<ObservableCollection<MyData>> queryPortalResult;

        var paramquery = System.Web.HttpUtility.ParseQueryString(req.Url.Query);

        string id = paramquery["id"] + "";

        string email = paramquery["email"] + "";

        string phone = paramquery["phone"] + "";

        if ((string.IsNullOrEmpty(id)) || (string.IsNullOrEmpty(email)))

            return new BadRequestObjectResult("ICCID or Email data are missing!");

        try

        {

            using (SqlConnection conn = new SqlConnection(connStr))

            {

                if (conn != null)

                {

                    await conn.OpenAsync();

                    if (conn.State != null)

                    {

                        string query1 = $"SELECT * FROM Customers WHERE EmailAddress = '\" + {email} + \"'";

                        using SqlCommand cmd1 = new(query1);

                        using SqlDataReader reader1 = await cmd1.ExecuteReaderAsync();

                        if (reader1.HasRows)

                        {

                            await reader1.ReadAsync();

                            if (((string)reader1["SimCard1ICCID"] == id) || ((string)reader1["SimCard2ICCID"] == id) || ((string)reader1["SimCard3ICCID"] == id) || ((string)reader1["SimCard4ICCID"] == id))

                            {

                                // Get authentication token

                                token = GetAccessTokenAsync(API_EMAIL + "", API_PASSWORD + "").Result + "";

                                queryPortalResult = QuerySimUsageData("GET-SUBSCRIBER-DATA", token, id, "");

                                if (queryPortalResult.Result.Count > 0)

                                {

                                    results = [.. queryPortalResult.Result];

                                }

                                if ((conn != null) && (string.IsNullOrEmpty((string)reader1["PhoneNumber"])))

                                {

                                    logger.LogInformation("Phone number save");

                                    string query2 = $"UPDATE Customers SET PhoneNumber = '\" + {phone} + \"' WHERE EmailAddress = '\" + {email} + \"'";

                                    using (SqlCommand cmd2 = new(query2))

                                    {

                                        if (cmd2 != null)

                                        {

                                            await cmd2.ExecuteNonQueryAsync();

                                        }

                                    }

                                }

                            }

                            await reader1.CloseAsync();

                            if (conn != null)

                            {

                                await conn.CloseAsync();

                            }

                            return new OkObjectResult(results);

                        }

                        else

                        {

                            await reader1.CloseAsync();

                            if (conn != null)

                            {

                                await conn.CloseAsync();

                            }

                            return new NotFoundObjectResult("No data found for the provided email.");

                        }

                    }

                    else

                    {

                        logger.LogError("Database connection failed.");

                        return new StatusCodeResult(500);

                    }

                }

                else

                {

                    logger.LogError("Database connection failed.");

                    return new StatusCodeResult(500);

                }

            }

        }

        catch (Exception ex)

        {

            logger.LogError($"Exception Error fetching Message: {ex.Message}");

            return new StatusCodeResult(500);

        }

    }

Regards,

Patrick M.

Erland Sommarskog 133K Reputation points MVP Volunteer Moderator

2026-02-24T22:49:57.76+00:00
I can't say on the top of my head why you would get that error for OpenAsync. I'm inclined to think that your analysis is not correct on that point.

However, see some examples of very bad practice elsewhere in your code:

string query1 = $"SELECT * FROM Customers WHERE EmailAddress = '" + {email} + "'";

This type of code where you inline parameter values into the string is entirely impermissible. You must use parameterised statements:

string query1 = $"SELECT * FROM Customers WHERE EmailAddress =@email"; cmd1.Parameters.Add("@email", SqlDbType.VarChar, 40).Value = email;

There are several reasons why the code you have is bad:

Opens for SQL injection.

Causes cache littering on the SQL Server side.

Is more difficult to get right. What if the text you interpolate includes a single quote.

It's a real nightmare when you do this with date and time values.

For a longer discussion, see this section from my article on dynamic SQL: https://www.sommarskog.se/dynamic_sql.html#ClientCode
Patrick M 0 Reputation points

2026-02-25T00:07:58.4966667+00:00

Got it. I'll do some cleanups based on your recommendations. Thank you very much!

1 answer

Your answer

Praveen Kumar Gudipudi 1,880 Reputation points Microsoft External Staff Moderator

2026-02-24T09:01:49.02+00:00

Hello Patrick M,

it’s either firewall or missing App Setting in Azure.

Please provide below required details:

How you're reading the connection string

Your Function runtime (.NET version)

Hosting plan (Consumption / Premium / Dedicated)
Erland Sommarskog 133K Reputation points MVP Volunteer Moderator

2026-02-24T22:49:57.76+00:00

I can't say on the top of my head why you would get that error for OpenAsync. I'm inclined to think that your analysis is not correct on that point.

However, see some examples of very bad practice elsewhere in your code:

string query1 = $"SELECT * FROM Customers WHERE EmailAddress = '" + {email} + "'";

This type of code where you inline parameter values into the string is entirely impermissible. You must use parameterised statements:

string query1 = $"SELECT * FROM Customers WHERE EmailAddress =@email"; cmd1.Parameters.Add("@email", SqlDbType.VarChar, 40).Value = email;

There are several reasons why the code you have is bad:

Opens for SQL injection.

Causes cache littering on the SQL Server side.

Is more difficult to get right. What if the text you interpolate includes a single quote.

It's a real nightmare when you do this with date and time values.

For a longer discussion, see this section from my article on dynamic SQL: https://www.sommarskog.se/dynamic_sql.html#ClientCode
Patrick M 0 Reputation points

2026-02-25T00:07:58.4966667+00:00

Got it. I'll do some cleanups based on your recommendations. Thank you very much!

Answer 1

The exception you are encountering when calling await connection.OpenAsync(); could be related to several factors, especially considering that you are working with a serverless Azure resource. Here are a few troubleshooting steps you can take:

Check Connection String: Ensure that your connection string is correctly formatted and that all parameters are valid. Pay attention to the server name, database name, user ID, and password. Make sure that the database is accessible from your Azure Function.
Network Issues: Since you are using a serverless Azure resource, check if there are any network restrictions or firewall rules that might be preventing your Azure Function from accessing the database. Ensure that the Azure Function has the necessary permissions to connect to the database.
Connection Timeout: The error message indicates a potential timeout issue. You might want to increase the Connection Timeout in your connection string to allow more time for the connection to be established.
Check for Null References: The stack trace mentions "Object reference not set to an instance of an object." This could indicate that some part of your code is trying to access a property or method on a null object. Ensure that all objects are properly instantiated before use.
Azure Function Configuration: Verify that your Azure Function's configuration settings (like connection strings) are set correctly in the Azure portal.
Logging: Utilize logging to capture more detailed information about the state of your application right before the connection attempt. This can help identify if any variables are not set as expected.

If you continue to experience issues after checking these areas, consider creating a support ticket with Azure for more in-depth assistance.

References:

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Azure function with a connection OPenAsync generates an exception

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