如何使用内存流代替文件流

Question

So what im trying to do is read a Select store procedure from my database save the data in a csv file and make it that the user is able to download it through the web application. I was able to get the requested result by saving the file temporary into my program foldel and using filestream. What i want to do now is skip the part where the file is saved onto my computer and temporary save it in the RAM memory instead. From what i understood i have to make use of memory stream instead of file stream but i dont really understand how i can do that. From what i understood from what i read is that instead of me making use of a file i need to convert my data to bytes make a memorystream out of it and then use it in my FileStreamResult. Am i correct here?

Method when i read from procedure and save to a csvfile:

public static String StoreApproved ()
{          
    string path1 = HttpRuntime.AppDomainAppPath + "Report.csv";
    SqlConnection sqlConnection1 = new SqlConnection("CONNECTIONSTRING");
    SqlCommand cmd = new SqlCommand();
    SqlDataReader reader;
    cmd.CommandText = "ExportApproved";
    cmd.CommandType = CommandType.StoredProcedure;
    cmd.Connection = sqlConnection1;
    sqlConnection1.Open();
    reader = cmd.ExecuteReader();
    List<ModelStoreProcedureApproved> TestList = new List<ModelStoreProcedureApproved>();
    ModelStoreProcedureApproved test ;

    while (reader.Read())
    {
        test = new ModelStoreProcedureApproved();
       // test.Id = int.Parse(reader["IdTimeTracker"].ToString());
        test.Month = reader["Month"].ToString();
        test.EmailUser = reader["Email"].ToString();
        test.Project = reader["Name"].ToString();
        test.Approved = reader["Description"].ToString();
        test.Month = reader["Month"].ToString();
        test.Year = reader["Year"].ToString();
        TestList.Add(test);
    }

    File.Create(path1).Close();
    var i = TestList.FirstOrDefault();
    using (TextWriter fileReader = new StreamWriter(path1))
    {
        var csv = new CsvWriter(fileReader);
        csv.Configuration.Encoding = Encoding.UTF8;
        foreach (var value in TestList)
        {
            csv.WriteRecord(value);
        }
        fileReader.Close();
    }
    sqlConnection1.Close();
    return path1;
}

Controller code:

public ActionResult ExportToCSV()
{
    string path = Repositories.UserRepository.StoreApproved();
    var fileStream = new FileStream(path,
                                    FileMode.Open,
                                    FileAccess.Read);

    return new FileStreamResult(fileStream, "text/csv") { FileDownloadName = "export.csv" };
}

Can someone explain me what the best way to do this is? Other posts i have read Serialize and Deserialize using BinaryFormatter

BinaryFormatter and Deserialization Complex objects

Using CSVHelper to output stream to browser

Answer 1

You can make it like this:

public static byte[] StoreApproved ()
{          
    string path1 = HttpRuntime.AppDomainAppPath + "Report.csv";
    SqlConnection sqlConnection1 = new SqlConnection("CONNECTIONSTRING");
    SqlCommand cmd = new SqlCommand();
    SqlDataReader reader;
    cmd.CommandText = "ExportApproved";
    cmd.CommandType = CommandType.StoredProcedure;
    cmd.Connection = sqlConnection1;
    sqlConnection1.Open();
    reader = cmd.ExecuteReader();
    List<ModelStoreProcedureApproved> TestList = new List<ModelStoreProcedureApproved>();
    ModelStoreProcedureApproved test ;

    while (reader.Read())
    {
        test = new ModelStoreProcedureApproved();
       // test.Id = int.Parse(reader["IdTimeTracker"].ToString());
        test.Month = reader["Month"].ToString();
        test.EmailUser = reader["Email"].ToString();
        test.Project = reader["Name"].ToString();
        test.Approved = reader["Description"].ToString();
        test.Month = reader["Month"].ToString();
        test.Year = reader["Year"].ToString();
        TestList.Add(test);
    }

    var i = TestList.FirstOrDefault();
    var mem = new MemoryStream();
    using (TextWriter fileReader = new StreamWriter(mem))
    {
        var csv = new CsvWriter(fileReader);
        csv.Configuration.Encoding = Encoding.UTF8;
        foreach (var value in TestList)
        {
            csv.WriteRecord(value);
        }
    }
    sqlConnection1.Close();
    return mem.ToArray();
}

public ActionResult ExportToCSV()
{
    byte[] bytes = Repositories.UserRepository.StoreApproved();
    Stream stream = new MemoryStream(bytes);
    return new FileStreamResult(stream, "text/csv") { FileDownloadName = "export.csv" };
}

Answer 2

I suggest you make clean separation of concerns since you are also using Asp.Net MVC. Instead of reading and creating memory stream inside same method, first read/get the data collection you need and just return the data out of the method. Then inside the action method you can decorate it with required format(binding to UI or returning a file etc.) based on your requirement

Though this is not be a straight answer to your question, and if all that you are looking for is using a memory stream, there are plenty of examples available to use for example as shown here and the answer you accepted etc.

Hope this help you.

Answer 3

        using (var ms = new MemoryStream())
        {
            using (var writer = new StreamWriter(ms))
            using (var csv = new CsvWriter(writer))
            {
                csv.WriteRecords({A list here});
            }
           ms.ToArray() // here is your actual data in memory stream
        }