Develop Reference

I want to back up the data in an xml file, I couldn't find how to save the newly received data without adding the same data to the existing file

I want to back up the data for today's date in an XML file every 10 minutes I managed to create the XML file, but I couldn't find how to save the newly received data without adding the same data to the existing file
Can I convert the file I created to dataSet with dataSet.ReadXml, add the new data I got from the query and convert it back to an XML file and save it? What method should I use?
String QueryString = "SELECT * FROM dbo.db_records WHERE DAY(datetime) = DAY(CURRENT_TIMESTAMP)";
public void run()
{
while (true)
{
try
{
Thread.Sleep(600000);
if (odbcConnection.State != ConnectionState.Open)
{
odbcConnection.Close();
odbcConnection.Open();
}
DataSet dataSet = new DataSet("XMLDB");
odbcDataAdapter.Fill(dataSet, "#ID");
if (File.Exists(Path))
{
}
else
{
using (FileStream fs = File.Create(Path))
{
dataSet.WriteXml(fs);
}
}
}
catch (Exception) { }
}
}

Xml is not a great format if you want to append data, since it uses tags that need to be closed. So you have a few options:
Save separate files
Since you seem to fetch data for the current day, just attach date-info to your file-name. When reading the data you may need to read all files in the folder fitting the pattern, and merge it.
Use a format that is trivial to append
If your data model is simple tabular data you may use a .csv file instead. You can add data to this using one of the File.Append methods.
Overwrite all data
Get the complete data you want to save each time, and overwrite any existing data. This is simple, but may be slow if you have lots of data. But if the database is small and grow slowly this might be perfectly fine.
Parse the existing data
You could read the existing file with Readxml as you suggest, and use DataSet.Merge to merge it with your new set before overwriting the existing file. This may also be slow, since it needs to process all the data. But it may put less load on the database than fetching all data from the database each time.
In any case, you might want to periodically save full backups, or have some other way to handle corrupt files. You should also have some way to test the backups. I would also consider using the backup options built into most database engines if that is an alternative.

Saving, loading and manipulating (listview) data C#

I'm working on an UWP application where a user can input data which is placed in a listview. All fine and dandy, but how can I save the user data to a separate file and load it the next time a user boots up the app?
I've tried to find a solution, but I had great difficulty to understand these code snippets and on how to apply these (since I'm fairly new to C# and App development). Would somebody like to explain how I can achieve the saving/loading of the data and explain what the code does?
Thanks in advance! :)

You can create a file like this:
StorageFile ageFile = await local.CreateFileAsync("Age.txt", CreationCollisionOption.FailIfExists);
I can read and write to a file like this:
StorageFolder local = Windows.Storage.ApplicationData.Current.LocalFolder;
var ageFile = await local.OpenStreamForReadAsync(#"Age.txt");
// Read the data.
using (StreamReader streamReader = new StreamReader(ageFile))
{
//Use like a normal streamReader
}
if you are trying to write, use OpenStreamForWriteAsync;

If I understood well, you have some kind of object structure that serves as a model for your ListView. When the application is started, you want to read a file where the data is present. When closing the application (or some other event) write the file with the changes done. Right?
1) When your application is loaded / closed (or upon modifications or some event of your choice), use the Windows.Storage API to read / write the text into the file.
2) If the data you want to write is just a liste of strings, you can save this as is in the file. If it is more complicated, I would recommend serializing it in JSON format. Use JSON.NET to serialize (object -> string) and deserialize (object <- string) the content of your file and object structure.
Product product = new Product();
product.Name = "Apple";
...
string json = JsonConvert.SerializeObject(product);

Displaying pdf files in a web page from a sql database directly without needing to save them to the server file system

I'm currently using an html embed tag to display a pdf file that is saved on the local server. Is there a wayo to display a pdf file on my page without having to save it to the local file system of the server? I just wand to pass it to the view from the controller in such a way that it can be displayed as a pdf in the page without having it stored on the file system directly.
Alternatively, is there a way to call a method to delete the pdf file from the server once the user has navigated away from the page they are viewing? How do I tell if th euser has navicated away from the page and how do i cause that to trigger a method that will delete the file?

I created a MVC class called PdfResult that returns a byte array as a PDF file.
The purpose is as follows (can't upload the source code, sorry):
PdfResult inherits from FileStreamResult
Set the Content-Type header to application/pdf
Set the Content-Disposition to either attachment or inline, and set an appropriate file name
Convert your data to a Stream -- if your data is a byte array, then write it to a MemoryStream.
See https://stackoverflow.com/a/16673120/272072 for a good example of how to do this.
Then, your embed code just needs to point to the action method, as if it was a PDF file.
Here's an example:
public ActionResult ShowPdf() {
// Note: the view should contain a tag like <embed src='MyController/GetPdf'>
return View();
}
public ActionResult GetPdf() {
byte[] pdfBytes = dataRepo.GetPdf(...);
return new PdfResult(pdfBytes, "Filename.pdf", false) ;
}

Here is a link to a CodeProject article and code sample titled Download and Upload Images from SQL Server via ASP.NET MVC. This gives an example of an efficient method to stream content to and from SQL Server via MVC.
You can easily adapt the code to stream your PDF file downloads.
UPDATE
The article uses a DataReader, but it can easily be adapted to Linq2Sql or EF. As an example, here is the Read method where I am reading from the database and copying to the stream:
public override int Read(byte[] buffer, int offset, int count)
{
result = _attachments.ExecuteStoreQuery<byte[]>(
"SELECT SUBSTRING(AttachmentBytes, " + position.ToString() +
", " + count.ToString() + ") FROM Attachments WHERE Id = {0}",
id).First();
var bytesRead = result.Length;
Buffer.BlockCopy(result, 0, buffer, 0, bytesRead);
position += bytesRead;
return (int)bytesRead;
}

You can read the PDF as a bytestream from the database and save it to the http response stream. If you have set the content type correctly to application/pdf, then the browser will load the document in the PDF plugin.
Update (14/Oct/2011): You need to write the bytestream to the Response.OutputStream object. How you create and write the byte stream is dependent on how you have stored in the database and how you are retrieving it. The following code snippet is from an article we have on our website - Generate PDF Forms In ASP.NET Using PDFOne .NET v3.
// Get the page's output stream ready
Response.Clear();
Response.BufferOutput = true;
// Make the browser display the forms document
// using a PDF plug-in. (If no plug in is available,
// the browser will show the File -> Save As dialog box.
Response.ContentType = "application/pdf";
// Write the forms document to the browser
doc.Save(Response.OutputStream);
doc.Close();
doc.Dispose();
The doc object is from our component. You need not use that. This code snippet is only for your understanding. For your requirement, you may have to something like bytestream.save(Response.OutputStream) I guess. BTW, this code is for ordinary ASP.NET, not MVC.
DISCLAIMER: I work for Gnostice.

If you want to create the PDF 100% dynamically, you would generate it completely in memory then stream it out directly to the requesting web browser without saving it as a file. This is very easy to do with the right tools. I would recommend AspPDF from Persits.com as a way to do this very easily. Take a look at their online documentation to see how simple this is to do without creating a bunch of rendered PDF files all over your server.
If you cannot do something like that, then simply incorporate a process to cleanup your "expired" PDF files from your server's filesystem based on their age. For example, after you have created your local PDF file, you just look through the folder containing your temporary PDF's and delete any you find over a certain age. You cannot reliably tell if or when a user has navigated away from your page or site.

For the first part of your question, like mentioned in the comments, use some type of stream object to pass the PDF data around. Right now, you are streaming the file to the local file system, then streaming it once again to the embedded tag for display. Just do away with the intermediate step of saving to the file system, and do the whole thing in memory (although, that's not really a model of efficiency, and might not scale well).
Regarding the second part of your question, that's not as straightforward. MVC really has no concept of state (viewstate, etc.), so it doesn't have events that can be fired from a state change (say, navigating away from a page).
You could use Javascript to detect a user navigating away from your page (windows.onunload), that calls a (C#/VB) method to remove the file from the file system. You would probably have to use AJAX to communicate back to the server, using an HTTP POST method, and have something listening at that URL endpoint to fire your method that removes the file.

WebClient.OpenReadAsync() corrupts JSON data. Why?

I have a class in my Silverlight app that (de-)serializes JSON strings to/from an object class.
I use WebClient.OpenReadAsync to get a file that contains this JSON string:
{"FirstName":"Bob","LastName":"Underwood"}
After calling OpenReadAsync however, the retrieved string has a lot of extra characters:
"PK\n\0\0\0\0\0�u�>h��5\0\0\05\0\0\0\t\0\0\0test.json\"{\\\"FirstName\\\":\\\"Gary\\\",\\\"LastName\\\":\\\"MacDonald\\\"}\"PK\0\n\0\0\0\0\0�u�>h��5\0\0\05\0\0\0\t\0\0\0\0\0\0\0\0\0 \0\0\0\0\0\0\0test.jsonPK\0\0\0\0\0\07\0\0\0\\\0\0\0\0\0"
This is the code I'm using to download the JSON:
WebClient client = new WebClient();
client.OpenReadCompleted += client_OpenReadCompleted;
client.OpenReadAsync(new Uri("/someJsonFile.zip", UriKind.Relative));
void client_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e) {
if (e.Error == null) {
StreamReader reader = new StreamReader(e.Result);
string jsonString = reader.ReadToEnd().ToString();
}
else {
addMessage("Error " + e.Error.ToString());
}
}
jsonString ends up with all that extra data, so I can't deserialize it as is.
Another thing to note: the URI points to someJsonFile.zip, but it's really not zipped, when I give the file a extension like .json, or no extension, I get a error that it cannot find the file, but when I give it a extension like .zip, it finds it fine. Is there a way I can use a normal or no extension? I was wondering if this was a configuration issue.
Questions:
Am I doing something wrong in pulling this file and using StreamReader to get the string that's causing me to get all that trash data?
Do I need to do something specific to be able to use WebClient to grab a file with different extensions, like .json, or even no extension at all?

1 - That data stream certainly is a ZIP (PK is the old PKZip marker and the test.json filename is mentioned in its index as well).
Your server may be setup to serve all files compressed (or you may simply be accessing an actual zip file). Please check the server settings.
2 - As for the second question, the WebClient does not care about file types. It is just a stream of data that needs to be interpreted by something that knows what the data is (i.e. your code).
It is only the server that may be configured to serve up different files in different ways.

I was able to figure things out with my domain provider, appears to have been some configuration issues on their end.

Silverlight Loading Reference Data On Demand from a 'dumb' server

I have a text file with a list of 300,000 words and the frequency with wich they occur. Each line is in the format Word:FequencyOfOccurence.
I want this information to be accessible from within the C# code. I can't hard code the list since it is too long, and I'm not sure how to go about accessing it from a file on the server. Ideally I'd ideally like the information to be downloaded only if it's used (To save on bandwidth) but this is not a high priority as the file is not too big and internet speeds are always increasing.
It doesn't need to be useable for binding.
The information does not need to be editable once the project has been built.

Here is another alternative. Zip the file up and stick it in the clientBin folder next to the apllication XAP. Then at the point in the app where the content is needed do something like this:-
public void GetWordFrequencyResource(Action<string> callback)
{
WebClient client = new WebClient();
client.OpenReadAsync += (s, args) =>
{
try
{
var zipRes = new StreamResourceInfo(args.Result, null)
var txtRes = Application.GetResourceStream(zipRes, new Uri("WordFrequency.txt", UriKind.Relative));
string result = new StreamReader(txtRes.Stream).ReadToEnd();
callback(result);
}
catch
{
callback(null); //Fetch failed.
}
}
client.OpenReadAsync(new Uri("WordFrequency.zip", UriKind.Relative"));
}
Usage:-
var wordFrequency = new Dictionary<string, int>();
GetWordFrequencyResource(s =>
{
// Code here to burst string into dictionary.
});
// Note code here is asynchronous with the building of the dictionary don't attempt to
// use the dictionary here.
The above code allows you to store the file in an efficient zip format but not in the XAP itself. Hence you can download it on demand. It makes use of the fact that a XAP is a zip file so Application.GetResourceStream which is designed to pull resources from XAP files can be used on a zip file.
BTW, I'm not actually suggesting you use a dictionary, I'm just using a dictionary as simple example. In reality I would imagine the file is in sorted order. If that is the case you could use a KeyValuePair<string, int> for each entry but create a custom collection type that holds them in an array or List and then use some Binary search methods to index into it.

Based on your comments, you could download the word list file if you are required to have a very thin server layer. The XAP file containing your Silverlight application is nothing more than a ZIP file with all the referenced files for your Silverlight client layer. Try adding the word list as content that gets compiled into the XAP and see how big the file gets. Text usually compresses really well. In general, though, you'll want to be friendly with your users in how much memory your application consumes. Loading a huge text file into memory, in addition to everything else you need in your app, may untimately make your app a resource hog.
A better practice, in general, would be to call a web service. The service could would perform whatever look up logic you need. Here's a blog post from a quick search that should get you started: (This was written for SL2, but should apply the same for SL3.)
Calling web services with Silverlight 2
Even better would be to store your list in a SQL Server. It will be much easier and quicker to query.

You could create a WCF service on the server side that will send the data to the Silverlight application. Once you retrieve the information you could cache it in-memory inside the client. Here's an example of calling a WCF service method from Silverlight.
Another possibility is to embed the text file into the Silverlight assembly that is deployed to the client:
using (var stream = Assembly.GetExecutingAssembly()
.GetManifestResourceStream("namespace.data.txt"))
using (var reader = new StreamReader(stream))
{
string data = reader.ReadToEnd();
// Do something with the data
}