Configuring Entity Framework for Oracle

Oracle needs two NuGet packages in order to work with Entity Framework: one to use at design time and one to use at run time. You'll need to make sure both of these are installed (and it doesn't help that their names are so similar):

  • ODP.NET, Managed Entity Framework Driver
  • ODP.NET, Managed Driver

You'll also need to install Oracle's ODP.NET_Managed_ODAC package.

As much as I'd like to pretend that I'm all-knowing but this information comes from Yonayli Gutierrez (Hi, Yonayli!) who took one of Learning Tree's ASP.NET MVC classes.

Posted by Peter Vogel on 01/05/2016 at 11:00 AM0 comments


Create Factory Functions in TypeScript for Creating Multiple Classes

In TypeScript, you can define a function that, when passed a set of parameters, creates and returns a correctly configured object. One of the parameters passed to the function must be the class of the object being created (I'll call that the "class parameter"). Normally, that means your factory function can only create a single kind of class but, by leveraging generics and interfaces, you can create functions that will create and configure a variety of classes.

Your first step is to define an interface that specifies the properties that your factory function will configure. Here's an example of an interface that specifies two properties:

interface ICustomer
{
  name: string;
  age: number;
}

With that interface in place you can create a generic factory function that works with any class that implements that interface. First, when defining your factory function, follow the factory function's name with a data type marker and specify that the marker extends the interface. Second, in the factory function's parameter list, use TypeScript's new keyword along with the generic data type marker when defining the function's class parameter (you're actually specifying the type of the class' constructor).

The following code shows the declaration of a generic factory function that leverages my ICustomer interface. I first provide a type marker (c) that, using the extend keyword, ties the function to classes that implement the ICustomer interface. I then use that type marker with the new keyword to specify the return type of the function's class parameter (called cust in my example):

function CreateCustomer<c extends ICustomer>(cust:{new(): c;}, 
                                             name: string, age: number): c
{

Now, inside my function, I use the class parameter to instantiate the class passed in the class parameter. Once I've done that, I can configure the object by setting the properties specified in the interface:

    var newCust: c;
    newCust = new cust();
    newCust.name = name;
    newCust.age = age;
    return newCust;
}

To use this factory, I pass the class I want created (which must implement the ICustomer interface) along with the rest of the parameters required by my factory function. This example:

var cust: Customer;
cust = CreateCustomer(Customer, "Peter", 62);

uses my function to create an instance of a class called Customer.

Posted by Peter Vogel on 12/28/2015 at 11:35 AM0 comments


Warn Developers about Using Your Old Code

At least two or three times in my life, I've come back to old systems I'd worked on and realized that I now knew a better way of doing things. However, rather than just revise existing code, that "better way of doing things" required me to write a new method, property or class. When I released my new code out into the world, I wanted to tell other developers to stop using my old code and move to my new code. The best way to do that, I've decided, is to go back to the old code and decorate it with the Obsolete attribute.

You can add the Obsolete attribute either to a class or to members of a class. Regardless, when a developer attempts to use the item you've decorated, they'll get a warning message in their code that says the class (or the member) you've decorated with the attribute is deprecated.

Of course, developers aren't likely to stop using your class or method unless you tell them about your alternative. You can do that by passing a message to the Obsolete attribute -- that message is then tacked onto the end of the attribute's default warning message. This example will generate the message "'SampleClass' is obsolete: Use PHVIS.NewClass" when someone tries to use SampleClass:

<Obsolete("Use PHVIS.NewClass")>
Public Class SampleClass
  Public Sub SampleMethod()

  End Sub
End Class

By default, the Obsolete attribute just generates a warning message so it won't stop the developer's code from compiling. If you want to be more aggressive, you can pass True as the attribute's second parameter to generate a compile-time error and prevent the developer's code from compiling, as this example does:

Public Class SampleClass
  <Obsolete("Use BetterMethod", True)>
  Public Sub SampleMethod()

  End Sub
End Class

I'd wait awhile before doing that, though.

Posted by Peter Vogel on 12/17/2015 at 10:57 AM0 comments


Wrapping Lines in Visual Studio

I was teaching Learning Tree's ASP.NET MVC course a few weeks back. The author of that course decided that having code lines extend past the right-hand edge of the code window wasn't a good idea if you're an instructor demoing some code. To eliminate those disappearing lines on the demo computer we use in the course, he turned on word-wrap for Visual Studio. This choice keeps all of the code on the screen by wrapping long lines of code back to the left hand margin.

If you like that idea, it's easy to turn on that option. Go to Tools | Options | Text Editor | All Languages and select the "Word wrap" choice on the right. That's all you need to do but, if you want, you can also have Visual Studio put a U-turn arrow at the end of each line that's too long to fit in the window -- just click the "Show Visual Glyphs for word wrap" option under the Word wrap choice.

Posted by Peter Vogel on 12/15/2015 at 11:04 AM0 comments


Create .zip Files from Code

If you've ever wanted to create a .zip file from your application, the System.IO.Compression.GZipStream will let you do it, assuming that you're comfortable with your file being in the industry-standard .gzip format (though I'm told you can swap in other compression schemes).

For this tip, I'm assuming that the file is small enough that you can read it all in one gulp. In that scenario, my first move is to define a FileStream object for the file I want to compress, read the file into memory, and close the FileStream:

Dim unCompressedFile As FileStream
unCompressedFile = File.OpenRead("C:\GreatBigFile.txt")
Dim bytes(5000) As Byte
Dim bytesRead As Integer
bytesRead = unCompressedFile.Read(bytes, 0, 5000)
unCompressedFile.Close()

My next move is to create a FileStream object for the compressed file I want to create:

Dim CompressedFile As FileStream
CompressedFile = File.Create("C:\IttyBittyFile.gzip")

With all the files in place, I'm ready to create the GZipStream object that will do the actual compression. You have to pass two parameters when creating the GZipStream object: The first is the FileStream for the compressed file you intend to create; the second indicates that you want to compress the file.

Here's my code to create a compressed file called IttyBittyFile.gzip:

Dim zipper As GZipStream
zipper = New GZipStream(CompressedFile, CompressionMode.Compress)

Now I can use the GZipStream Write method to write out the compressed file, passing the bytes I retrieved from the original file:

zipper.Write(bytes, 0, bytesRead)

Finally, of course, I close the GZipStream object and my compressed file:

zipper.Close()
CompressedFile.Close()

As you probably suspect, if you change the CompressionMode and pass in a compressed file, you can use GZipStream to decompress a file.

Posted by Peter Vogel on 12/10/2015 at 9:46 AM0 comments


Creating a NuGet Web Site

In my regular Practical.NET column, I showed how easy it is to create NuGet packages and discussed how it was a much better way for a developer to share anything you've created, from Entity Framework classes to JavaScript files (my example was a package that implemented an HtmlHelper consisting of a DLL and a JavaScript file). NuGet also allows you to attach searchable documentation to your package to ensure that a developer can find your package, recognize it and know what your code does.

In that article, I showed how to use a folder as a repository for NuGet packages. But if you'd like something a little more professional, you can create a NuGet Web site. It's easy to do: First, in Visual Studio, create an Empty Web Application. Once the project appears in Solution Explorer, right-click on it and select Manage NuGet Packages. In the NuGet Package Manager, do a search for the NuGet.Server package and install it.

After deploying your Website, you just need to do two things:

  1. Save your NuGet packages into the Packages folder in your new site.
  2. Tell Visual Studio about your site.

My earlier article walks through both processes. You can get the information for your site by surfing to it with your browser -- its default page provides both the file path to the folder you should save your package in and the URL you should use when telling Visual Studio about your NuGet site.

I'll put in one caveat: I only tested this on IIS 7.

Posted by Peter Vogel on 12/03/2015 at 10:18 AM0 comments


Stop Being Bugged About Changed Files

Every once in a while, you have a file open in one of your Visual Studio tabs and the file is updated on the disk. Unlike when any unopened files/folders in Solution Explorer are changed, Visual Studio notices this change. The result is that you get a dialog telling you that the “file has been modified outside of the editor” and are asked if you “want to reload it?” There are, essentially, two buttons on the dialog: Yes and No.

I have never clicked No. Not once. Not ever.

So, the other day, I took the plunge and turned off this dialog: I shouldn’t ever see that message again. Instead, my changed file will be quietly refreshed. If you also want to get rid of the dialog, first go to the Tools menu and select Options. From the Environment treeview on the left side of the resulting dialog, drill down to the Documents node and, on the right, check the option under “Detect when file is changed.” This will cause Visual Studio to skip the dialog and just reload the changed version of the file.

Depending on which version of Visual Studio you have, that option will be called “Autoload Changes, If Saved” or the more obvious “Reload modified files unless there are unsaved changes.” Either way, as long as you haven’t made changes to the file, the changed file will automatically (and silently) be refreshed in the editor tab. If you’ve made changes to the file and haven’t saved them yet, you’ll get a dialog asking if you want to keep your changes.

Quite frankly, I don’t know why it isn’t the default.

Posted by Peter Vogel on 11/17/2015 at 9:43 AM0 comments


Protecting Shared Fields in Asynchronous Processing

Sometimes, in a C# application with multiple threads running simultaneously, you need to share data. So you set up a variable declared outside of any method or property (a "field") and have the different threads share data by updating and reading that variable. It should work ... but it doesn't and you can't figure out why.

The odds are that there's some bug in your asynchronous code that's creating the problem. However (and this is a long shot), it might be the compiler's fault. Some of the optimizations the compiler applies to a field assume that the field will only be accessed by a single thread at a time. This means your source code might look fine ... but the optimized code you're executing is doing something different.

There are two solutions in C#: First, put a lock around any code that accesses the field (this option is also available in Visual Basic). You might take a hit on performance as threads queue up to get to your field, but it ensures that you both keep the compiler's optimizations and have only one thread accessing the field at a time.

If you don't think you can find all the places that the field is being read or written (or are too lazy to look) you can, in C#, mark the variable as volatile:

internal volatile string Status;

The volatile keyword causes the compiler to omit the optimizations that assume single-thread access. You'll still take a performance hit because, internally, the compiler will cause reads and writes to your variable to be processed in sequence. But, now, when your application still doesn't work, you'll know it's your fault.

Visual Basic doesn't have an equivalent to the volatile keyword. However, if you can track down all the places where you read or write the field, you can use the Thread object's VolatileRead and VolatileWrite methods when working with the field.

Posted by Peter Vogel on 11/04/2015 at 10:07 PM0 comments


Properties with Parameters (and Making Them the Default)

Most developers aren't aware that you can write properties that accept parameters, just like a method does. Of course, it isn't often that you need a property that accepts a parameter. One way I recognize that I could use a property rather than a method is when my method name begins with the word "Get." Here, for example, is a method that (I assume) returns the specified part of a name:

Public Class NameManager
  Public Function GetNamePart(NamePosition As Integer) As String
    '...code
  End Function

If I rewrite the method as a property (and rename it), my class code looks like this:

Public Class NameManager
  Public ReadOnly Property NamePart(NamePosition As Integer) As String
    Get
      '...code
    End Get
  End Property

A developer who wants to get the customer's middle name would write code like this:

Dim nm As New NameManager("Peter Hunter Vogel")
Dim middleName As String
middleName = nm.NamePart(2)

You can go one step further and make this property the default property for the class, in which case a developer doesn't even have to use the property name. Here's the relevant code in Visual Basic (which adds the modifier Default to the property's signature):

Public Class NameManager
  Default Public ReadOnly Property NamePart(NamePosition As Integer) As String
    Get
      '...code
    End Get
  End Property

Here it is in C# (which renames the property to the keyword "this"):

public class NameManager
  public string this(int NamePosition) 
    get {
      '...code
   }

Regardless of how the class is written, the code to retrieve the middle name now looks like this:

middleName = nm(2)

Posted by Peter Vogel on 10/29/2015 at 3:12 PM0 comments


Why Won't My Razor Code Compile!?!

I've said it before: The Razor code that I enter into my ASP.NET MVC Views looks like magic to me. The ability Razor gives me to mix HTML and code surpasses my understanding. But, like magic, because I don't understand why Razor works, there are times where I don't understand why Razor doesn't work.

And neither do my clients, one of whom called me up last week to ask why code like the following wasn't acceptable to Razor (in C#, equivalent code wouldn't require the second @ ... but it still wouldn't compile):

@If RowRequired Then
  @<tr>
End If

The problem is that, inside a code block (like this If…Then block), Razor requires that all open tags have a matching close tag. Razor is fine with this code, for example:

@If RowRequired Then
  @<tr></tr>
End If

This can make structuring your HTML a little more awkward but, there is a solution: use @: instead of plain old @. With @:, this code compiles:

@If RowRequired Then
  @:<tr>
End If
</tr>

That's sharp!

Posted by Peter Vogel on 10/23/2015 at 1:16 PM0 comments


Catching Every Keystroke with jQuery

In an earlier column I used the jQuery change function to wire up a function to run after a user makes a change to an entry in a textbox. That "after" is important because the function I wired up won't run when the user makes a change in a textbox -- the event waits until the user leaves the textbox before firing.

In that article I mentioned, in passing, that if you really did want to catch a change as soon as a user makes it, you want to wire up the oninput event: The oninput event really does fire as soon as the user makes any change in a textbox. The major issue with oninput is that it's only available in browsers that support that portion of the HTML5 specification.

Unlike many other HTML events there's no built-in jQuery function to pick up the oninput event, so you need to use the jQuery on function to wire up a function to the event.

Here's some code that wires up a function that displays an alert box as soon as the user makes a change:

$(":text").on("input", function () { alert("got it"); });

You'll notice in my code that I'm using the :text selector, which only wires my function up to textboxes (it doesn't attach other input elements like passwords or checkboxes and also ignores dropdown lists and textareas). Several of the elements I'm skipping don't need the oninput event because the jQuery change event fires as soon as the user makes a change: Checkboxes and dropdown lists fall into that group. Password textboxes and textareas don't get caught by the :text selector, however, so you'll need to use more selectors to catch events immediately with them.

Posted by Peter Vogel on 10/13/2015 at 10:43 AM0 comments


Returning Server-Side Errors from AJAX Calls

In ASP.NET MVC if you call an action method on the server from JavaScript code and that action method raises an exception, you'll get an error at the client that lets you know something has gone wrong. Unfortunately, all the information you typically get is the HTTP 500 error status code and it's default message.

If you want to get your own custom error message delivered to the client, you could create your own custom error object and return it from the server when something goes wrong. Unfortunately, with that solution jQuery won't call the error function you specified in your $.ajax call -- you'll have to write your own code to check if the object returned from the server is your error object .

A better solution is to instantiate and return your own HttpStatusCodeResult, which does cause jQuery to call the error function you specify in your $.ajax call. This server-side code will do the trick, while providing a custom message to go down to the client:

return new HttpStatusCodeResult(410, "Unable to find customer.")

On the client, your message will be in the third parameter passed to your error function.

If you're handling multiple error conditions in the same action method and need to take different actions at the client depending on the error, you can give each error a different status code. If so, in your client code you'll need to check the error status code to see what error has triggered your error function. The error code is returned in the status property of the first parameter passed to your error method.

This client-side example calls a server-side method and, if the method returns a 410 error, displays my custom error message to the user:

$.ajax({url:'/home/deleteCustomer',
  data: {id: "A123"),
  success: function (result) {//handle successful execution},
  error: function (xhr, httpStatusMessage, customErrorMessage) {
    if (xhr.status === 410) {
      alert(customErrorMessage);}}});

Here's the list of defined HTTP status codes. If your message is suggesting that the error is something that the user can fix, then you should probably pick a code from the 400 series (that series is reserved for client errors). Personally, I don't think developers are using status code 418 ("I'm a teapot") enough.

Posted by Peter Vogel on 10/07/2015 at 11:28 AM0 comments


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