Writing using TableOutput, Reading using TableClient: String to Int cast error

Question

I have the following class:

public class MyData
{
  public string PartitionKey { get; set; }
  public string RowKey { get; set; }
  public int NumOranges { get; set; }
  public int NumApples { get; set; }
  public int NumBananas { get; set; }
}

I am writing instances to Azure Table Storage using the .NET 8 Isolated Azure Functions TableOutput binding.

When I attempt to read the data using Azure.Data.Table.TableClient (v12.10.0) like this:

  var result = tableClient.Query<MyData>(filter: d => d.PartitionKey = 'val');

I get Unable to cast object of type 'System.String' to type 'System.Int32' errors.

I though table storage was schema-less.

If I change the type of all my int properties to long then it works. I can use that as a workaround but I would love to know the cause and if I can do something more preventative or logical about it.

The issue is not to do with the actual values. All values are well within the Int32.MaxValue. I have double-checked by getting the data as TableEntity and checked the Max() of each property.

Answer 1

Azure Table Storage stores numbers as long (Edm.Int64), so I have used Convert.ToInt32(entity["PropertyName"]) to read them as int and avoid type mismatches.

ReadFromTableStorage.cs :

using System.Net;
using Azure.Data.Tables;
using Microsoft.Azure.Functions.Worker;
using Microsoft.Azure.Functions.Worker.Http;
using Microsoft.Extensions.Logging;
using System.Text.Json;
using Azure;
using FunctionApp28.Models;

namespace FunctionApp28.Functions
{
    public static class ReadFromTableStorage
    {
        [Function("ReadFromTableStorage")]
        public static async Task<HttpResponseData> Run(
            [HttpTrigger(AuthorizationLevel.Function, "get")] HttpRequestData req,
            FunctionContext executionContext)
        {
            var logger = executionContext.GetLogger("ReadFromTableStorage");
            logger.LogInformation("Reading from Azure Table Storage...");

            string connectionString = Environment.GetEnvironmentVariable("AzureWebJobsStorage");
            string tableName = "kamtable";

            if (string.IsNullOrEmpty(connectionString))
            {
                logger.LogError("AzureWebJobsStorage connection string is missing.");
                var errorResponse = req.CreateResponse(HttpStatusCode.InternalServerError);
                await errorResponse.WriteStringAsync("Storage connection string not found.");
                return errorResponse;
            }

            try
            {
                var tableClient = new TableClient(connectionString, tableName);
                Pageable<TableEntity> entities = tableClient.Query<TableEntity>();
                var resultList = new List<MyData>();
                foreach (var entity in entities)
                {
                    resultList.Add(new MyData
                    {
                        PartitionKey = entity.PartitionKey,
                        RowKey = entity.RowKey,
                        NumOranges = entity.ContainsKey("NumOranges") ? Convert.ToInt32(entity["NumOranges"]) : 0,
                        NumApples = entity.ContainsKey("NumApples") ? Convert.ToInt32(entity["NumApples"]) : 0,
                        NumBananas = entity.ContainsKey("NumBananas") ? Convert.ToInt32(entity["NumBananas"]) : 0
                    });
                }

                var response = req.CreateResponse(HttpStatusCode.OK);
                await response.WriteStringAsync(JsonSerializer.Serialize(resultList));
                return response;
            }
            catch (Exception ex)
            {
                logger.LogError($"Error reading from Table Storage: {ex.Message}");
                var errorResponse = req.CreateResponse(HttpStatusCode.InternalServerError);
                await errorResponse.WriteStringAsync($"Error retrieving data: {ex.Message}");
                return errorResponse;
            }
        }
    }
}

WriteToTableStorage.cs :

using System.Net;
using Azure.Data.Tables;
using Microsoft.Azure.Functions.Worker;
using Microsoft.Azure.Functions.Worker.Http;
using Microsoft.Extensions.Logging;
using Newtonsoft.Json;
using FunctionApp28.Models;

namespace FunctionApp28.Functions
{
    public static class WriteToTableStorage
    {
        private const string TableName = "kamtable";
        [Function("WriteToTableStorage")]
        public static async Task<HttpResponseData> Run(
            [HttpTrigger(AuthorizationLevel.Function, "post")] HttpRequestData req,
            FunctionContext context)
        {
            var logger = context.GetLogger("WriteToTableStorage");
            string requestBody = await new StreamReader(req.Body).ReadToEndAsync();
            var data = JsonConvert.DeserializeObject<MyData>(requestBody);

            if (data == null)
            {
                var badResponse = req.CreateResponse(HttpStatusCode.BadRequest);
                await badResponse.WriteStringAsync("Invalid request payload.");
                return badResponse;
            }

            string connectionString = Environment.GetEnvironmentVariable("AzureWebJobsStorage");
            var tableClient = new TableClient(connectionString, TableName);
            await tableClient.CreateIfNotExistsAsync();

            var entity = new TableEntity(data.PartitionKey, data.RowKey)
            {
                { "NumOranges", data.NumOranges },
                { "NumApples", data.NumApples },
                { "NumBananas", data.NumBananas }
            };

            await tableClient.AddEntityAsync(entity);
            logger.LogInformation("Data written to table storage successfully.");
            var response = req.CreateResponse(HttpStatusCode.OK);
            await response.WriteStringAsync("Entity written to Table Storage.");
            return response;
        }
    }
}

MyData.cs :

namespace FunctionApp28.Models
{
    public class MyData
    {
        public string PartitionKey { get; set; }
        public string RowKey { get; set; }
        public int NumOranges { get; set; }
        public int NumApples { get; set; }
        public int NumBananas { get; set; }
    }
}

Output :

I have sent the below POST request.

{
    "PartitionKey": "Fruit",
    "RowKey": "123",
    "NumOranges": 5,
    "NumApples": 10,
    "NumBananas": 3
}