What is the difference between const and readonly?

[Origin]: https://stackoverflow.com/questions/55984/what-is-the-difference-between-const-and-readonly

Apart from the apparent difference of

  • having to declare the value at the time of a definition for a const VS readonly values can be computed dynamically but need to be assigned before the constructor exits.. after that it is frozen.
  • ‘const’s are implicitly static. You use a ClassName.ConstantName notation to access them.

There is a subtle difference. Consider a class defined in AssemblyA.

public class Const_V_Readonly
{
  public const int I_CONST_VALUE = 2;
  public readonly int I_RO_VALUE;
  public Const_V_Readonly()
  {
     I_RO_VALUE = 3;
  }
}

AssemblyB references AssemblyA and uses these values in code. When this is compiled,

  • in the case of the const value, it is like a find-replace, the value 2 is ‘baked into’ the AssemblyB‘s IL. This means that if tomorrow I’ll update I_CONST_VALUE to 20 in the future. AssemblyB would still have 2 till I recompile it.
  • in the case of the readonly value, it is like a ref to a memory location. The value is not baked into AssemblyB‘s IL. This means that if the memory location is updated, AssemblyB gets the new value without recompilation. So if I_RO_VALUE is updated to 30, you only need to build AssemblyA. All clients do not need to be recompiled.

So if you are confident that the value of the constant won’t change use a const.

public const int CM_IN_A_METER = 100;

But if you have a constant that may change (e.g. w.r.t. precision).. or when in doubt, use a readonly.

public readonly float PI = 3.14;

Update: Aku needs to get a mention coz he pointed this out first. Also I need to plug where I learned this.. Effective C# – Bill Wagner

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Single controller with multiple GET methods in ASP.NET Web API

[Origin]: https://stackoverflow.com/questions/9499794/single-controller-with-multiple-get-methods-in-asp-net-web-api

In Web API I had a class of similar structure:

public class SomeController : ApiController
{
    [WebGet(UriTemplate = "{itemSource}/Items")]
    public SomeValue GetItems(CustomParam parameter) { ... }

    [WebGet(UriTemplate = "{itemSource}/Items/{parent}")]
    public SomeValue GetChildItems(CustomParam parameter, SomeObject parent) { ... }
}

Since we could map individual methods, it was very simple to get the right request at the right place. For similar class which had only a single GET method but also had an Object parameter, I successfully used IActionValueBinder. However, in the case described above I get the following error:

Multiple actions were found that match the request: 

SomeValue GetItems(CustomParam parameter) on type SomeType

SomeValue GetChildItems(CustomParam parameter, SomeObject parent) on type SomeType

I am trying to approach this problem by overriding the ExecuteAsync method of ApiController but with no luck so far. Any advice on this issue?

Edit: I forgot to mention that now I am trying to move this code on ASP.NET Web API which has a different approach to routing. The question is, how do I make the code work on ASP.NET Web API?

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This is the best way I have found to support extra GET methods and support the normal REST methods as well. Add the following routes to your WebApiConfig:

routes.MapHttpRoute("DefaultApiWithId", "Api/{controller}/{id}", new { id = RouteParameter.Optional }, new { id = @"\d+" });
routes.MapHttpRoute("DefaultApiWithAction", "Api/{controller}/{action}");
routes.MapHttpRoute("DefaultApiGet", "Api/{controller}", new { action = "Get" }, new { httpMethod = new HttpMethodConstraint(HttpMethod.Get) });
routes.MapHttpRoute("DefaultApiPost", "Api/{controller}", new {action = "Post"}, new {httpMethod = new HttpMethodConstraint(HttpMethod.Post)});

I verified this solution with the test class below. I was able to successfully hit each method in my controller below:

public class TestController : ApiController
{
    public string Get()
    {
        return string.Empty;
    }

    public string Get(int id)
    {
        return string.Empty;
    }

    public string GetAll()
    {
        return string.Empty;
    }

    public void Post([FromBody]string value)
    {
    }

    public void Put(int id, [FromBody]string value)
    {
    }

    public void Delete(int id)
    {
    }
}

I verified that it supports the following requests:

GET /Test
GET /Test/1
GET /Test/GetAll
POST /Test
PUT /Test/1
DELETE /Test/1

Note That if your extra GET actions do not begin with ‘Get’ you may want to add an HttpGet attribute to the method.

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How to remove error about glyphicons-halflings-regular.woff2 not found

[Origin]: https://stackoverflow.com/questions/32300578/how-to-remove-error-about-glyphicons-halflings-regular-woff2-not-found

This problem happens because IIS does not know about woff and woff2 file mime types.

Solution 1:

Add this lines in your web.config project:

 <system.webServer>
  ...
  </modules>
    <staticContent>
      <remove fileExtension=".woff" />
      <mimeMap fileExtension=".woff" mimeType="application/x-font-woff" />
      <remove fileExtension=".woff2" />
      <mimeMap fileExtension=".woff2" mimeType="application/font-woff2" />
    </staticContent>

Solution 2:

On IIS project page:

Step 1: Go to your project IIS home page and double click on MIME Types button:

Step 1

Step 2: Click on Add button from Actions menu: Step 2

Step 3: In the middle of the screen appears a window and in this window you need to add the two lines from solution 1: Step 3

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The ‘Access-Control-Allow-Origin’ header contains multiple values

[Origin]: https://stackoverflow.com/questions/37594403/the-access-control-allow-origin-header-contains-multiple-values

i’m trying to send get request to api like it’s a login url

var url = "http://demo.software.travel/gptp/api/authorization?apiKey=****&amp;alias=****&amp;login=****&amp;password=****"
$.get(url, function(data) {
    console.log(data);
});

i’m getting this in my console this error

XMLHttpRequest cannot load http://demo.software.travel/gptp/api/authorization?apiKey=****&alias=****&login=****&password=****. 
The 'Access-Control-Allow-Origin' header contains multiple values 'http://travellights.net, *', but only one is allowed. 
Origin 'http://travellights.net' is therefore not allowed access.

i’m trying to see questions here to solve it but i didn’t get what i need to change, this is annoying actually.

The ‘Access-Control-Allow-Origin’ header contains multiple values

this solved by asp.net web.congif

By the way i’m using CHROME BROWSER any help i appreciate.

UPDATE response headers:

Access-Control-Allow-Credentials:true
Access-Control-Allow-Credentials:true
Access-Control-Allow-Headers:origin, x-requested-with, Content-Type, accept, Token
Access-Control-Allow-Methods:GET, HEAD, POST, PUT, DELETE, TRACE, OPTIONS
Access-Control-Allow-Origin:http://travellights.net
Access-Control-Allow-Origin:*
Connection:close
Content-Encoding:gzip
Content-Type:application/json;charset=utf-8
Date:Thu, 02 Jun 2016 16:41:18 GMT
Server:nginx/1.1.19
Set-Cookie:JSESSIONID=51FEE1A1206B9B481DD3EEA4167A9256; Path=/gptp
Vary:Origin
Vary:Accept-Encoding
X-UA-Compatible:IE=EmulateIE7

Request Headers:

Accept:application/json, text/javascript, */*; q=0.01
Accept-Encoding:gzip, deflate, sdch
Accept-Language:en-US,en;q=0.8,ar;q=0.6,en-GB;q=0.4
Connection:keep-alive
Host:demo.software.travel
Origin:http://travellights.net
Referer:http://travellights.net/b2b/Pages/login?
User-Agent:Mozilla/5.0 (Windows NT 10.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/50.0.2661.102 Safari/537.36
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You are attempting to do Cross-origin resource sharing (CORS) which is a mechanism that allows restricted resources on a web page to be requested from another domain outside the domain from which the resource originated. (such as accessing fonts or JSON files).

Browsers restrict your access to resources from other origins as of Same-origin policy as a security measure for internet users.

To get around this issue you have to options:

  1. allow CORS on the domain http://demo.software.travel (but there is are security concerns, more description about it here: https://www.owasp.org/index.php/HTML5_Security_Cheat_Sheet#Cross_Origin_Resource_Sharing)

Enable CORS on the server to be able to access other domains through. this can be done by adding the following headers to responses:

Access-Control-Allow-Origin: http://travellights.net Access-Control-Allow-Headers: Origin, X-Requested-With, Content-Type, Accept
  1. if you are not granted resource sharing with that domain, you are allowed to use JSONP for read only operations (JSONP is inherently read-only)

JSONP wraps a JSON object in a callback, which technically makes the request a non-restricted resource (a script tag) hence can be shared across domains.

it can be done via vanilla js by adding a script tag onto the page.

function process(data) {
    // do stuff with JSON
}

var script = document.createElement('script');
script.src = '//domainURL?callback=process'

document.getElementsByTagName('head')[0].appendChild(script);

or you can use jquery to achieve the same:

$.ajax({enter code here
    url: "http://query.yahooapis.com/v1/public/yql",
    jsonp: "callback",
    dataType: "jsonp",
    data: {
        q: "select title,abstract,url from search.news where query=\"cat\"",
        format: "json"
    },
    success: function( response ) {
        console.log( response ); // server response
    }
});

jquery documentation: https://learn.jquery.com/ajax/working-with-jsonp/

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If you set “Full” CORS (with OPTION pre-request) on in nginx by add ‘access-control-allow-origin *’ and independently you add that header (for Simple CORS – without OPTION pre-request) to each response in SERVER (eg. php):

header('Access-Control-Allow-Origin', "*");

Then you will get this problem. Solution: remove code which add this header in server if already you add this header in your nginx config 🙂

I found this advice here

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How to return a value from a stored procedure to EF

[Origin]: https://stackoverflow.com/questions/35352605/how-to-return-a-value-from-a-stored-procedure-to-ef

I’m attempting to call a stored proc through EF and retrieve a return value from the stored proc. I’ve used this answer as a guide. Here is my stored proc:

CREATE PROCEDURE [dbo].[usp_test]
(
    @result int OUT
)
AS
BEGIN

--DO STUFF

SET @result = 0
END

Here is how I’m calling it from EF:

var status = new SqlParameter
{
    ParameterName = "result",
    DbType = DbType.Int32,
    Direction = ParameterDirection.Output 
};
var result = context.Database.SqlQuery&lt;int&gt;("EXEC usp_test @result", status);
var wasSuccessful = result.First() == 1;
if (!wasSuccessful)
{
    //DO STUFF
}

I’m getting this error message:

The data reader has more than one field. Multiple fields are not valid for EDM primitive or enumeration types

What am I doing wrong?

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Try select @result before end of procedure.

CREATE PROCEDURE [dbo].[usp_test]
(
    @result int OUT
)
AS
BEGIN

--DO STUFF

SET @result = 0
Select @result
END

Hope it works.

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Why does my JavaScript get a “No ‘Access-Control-Allow-Origin’ header is present on the requested resource” error when Postman does not?

[Origin]: https://stackoverflow.com/questions/20035101/why-does-my-javascript-get-a-no-access-control-allow-origin-header-is-present

I am trying to do authorization using JavaScript by connecting to the RESTful API built in Flask. However, when I make the request, I get the following error:

XMLHttpRequest cannot load http://myApiUrl/login. No ‘Access-Control-Allow-Origin’ header is present on the requested resource. Origin ‘null’ is therefore not allowed access.

I know that the API or remote resource must set the header, but why did it work when I made the request via the Chrome extension Postman?

This is the request code:

$.ajax({
    type: "POST",
    dataType: 'text',
    url: api,
    username: 'user',
    password: 'pass',
    crossDomain : true,
    xhrFields: {
        withCredentials: true
    }
})
    .done(function( data ) {
        console.log("done");
    })
    .fail( function(xhr, textStatus, errorThrown) {
        alert(xhr.responseText);
        alert(textStatus);
    });

If I understood it right you are doing an XMLHttpRequest to a different domain than your page is on. So the browser is blocking it as it usually allows a request in the same origin for security reasons. You need to do something different when you want to do a cross-domain request. A tutorial about how to achieve that is Using CORS.

When you are using postman they are not restricted by this policy. Quoted from Cross-Origin XMLHttpRequest:

Regular web pages can use the XMLHttpRequest object to send and receive data from remote servers, but they’re limited by the same origin policy. Extensions aren’t so limited. An extension can talk to remote servers outside of its origin, as long as it first requests cross-origin permissions.

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For C# web services – webapi

Please add the following code in your web.config file under <system.webServer> tag. This will work.

<httpProtocol>
    <customHeaders>
        <add name="Access-Control-Allow-Origin" value="*" />
    </customHeaders>
</httpProtocol>

Please make sure you are not doing any mistake in the Ajax call.

jQuery

$.ajax({
    url: 'http://mysite.microsoft.sample.xyz.com/api/mycall',
    headers: {
        'Content-Type': 'application/x-www-form-urlencoded'
    },
    type: "POST", /* or type:"GET" or type:"PUT" */
    dataType: "json",
    data: {
    },
    success: function (result) {
        console.log(result);
    },
    error: function () {
        console.log("error");
    }
});

Angular 4 issue, please refer to How to fix Angular 4 API call issues.

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How to retrieve output parameter from stored procedure in Entity Framework

[Author]: https://code.msdn.microsoft.com/How-to-retrieve-output-e85526ba

How to get output parameter in stored procedure from Entity Framework(CSEFOutputParameter)

Introduction

This sample demonstrates how to use ObjectParameter instance to get the value of output parameter in Entity Framework.

Building the Sample

  1. Start Visual Studio 2012 and select File > Open > Project/Solution.
  2. Go to the directory in which you download the sample. Go to the directory named for   the sample, and double-click the Microsoft Visual Studio Solution (.sln) file.
  3. Attach the database file EFDemoDB.mdf under the folder _External_Dependencies to your SQL Server 2008R2 database instance.
  4. Modify the connection string in the App.config according to your SQL Server 2008R2 database instance name.
  5. Press F7 or use Build > Build Solution to build the sample.

Running the Sample

  1. Right click the solution and built it.
  2. Press F5 to run the project, a console window will appear.

3

3.Follow the prompt to input person information.

Using the Code

Stored Procedure

ALTER PROCEDURE [dbo].[InsertPerson]    
@Name varchar(50),    
@Description varchar(200),      
@ID int OUT    
AS    
INSERT INTO Person(Name,Description) VALUES(@Name,@Description)    
SET @ID = SCOPE_IDENTITY() 

The code below demonstrates how to get the value of output parameter.

// Create a ObjectParameter instance to retrieve output parameter from stored procedure 
ObjectParameter Output = new ObjectParameter("ID", typeof(Int32)); 
context.InsertPerson(Name, Description, Output);   

Console.Write("ID: {0}", Output.Value);