Exposing child class in Swagger documentation

Hello All,

Writing this post after a long time, will make sure to keep continue sharing my knowledge

Problem Statement: 

Need to expose inherited / child class into Swagger documentation

Use case:

This is very common issue, where you have multiple inheritance classes in your MVC application. And you need to expose all your child classes into Swagger documentation to make sure Solution/System Integrator should have visibility to use all possible cases based on their requirement.  

Solution:

In WCF we have to decorate class by adding KnownType attribute to all your child class. In latest version of swagger new decoration has been added which is SwaggerSubTypes.

You have to decorate your all child class with SwaggerSubTypes attribute, this accepts array of types to expose all your child classes

Consider you have one base class Computer and two inherited classes Laptop and Desktop. You have exposed API to create new peripherals  

So base class have two properties, we will create two new base class to create inheritance 

Our goal is to expose all three object definition in Swagger, so for that lets add decoration to these classes

If you want to hide Computer then mark it as abstract. 

For this to get working in your code, you need to add few lines in Startup.cs file, copy below lines into ConfigureServices function

    services.AddSwaggerGen(c =>
    {
        c.EnableAnnotations(enableSubTypeAnnotations: true);
    });

You are done!

Exposing property as OperationContract in WCF

Hello All,

I would like to share thing which I just learn today J

In WCF usually we work with operation contract i.e. methods. I was trying to expose property not a method. I found solution and here is the way it should be

Simple Service Contract

Contract Implementation

Nothing fancy, and here is client to call this service and its output

So before we go further, I would like to make you clear about what we are going to do.. So requirement is I don’t want to change DoWork signature, but still want to add some additional information which DoWork should use if available, means a kind of optional parameter I would like to add.

For that I need to add property and get it exposed into client. So my new service contract will something similar as bellow

You can see, one new property Message added with only set, as I want to be as one-way. To Expose property you have to write OperationContract attribute ot get or set not on top of member just we do with method.

Now change little bit in logic to use Message if it’s there if not then behave normally.

After updating reference, I can see WCF internally convert my Message property into method by adding set_ prefix.

Let’s set message and will call my work method again.

Demm it, doesn’t work! It’s fairly simple and straightforward!!! Where is the issue? @#$%$@@#$

In debug I can see message is set property to my private variable…

but when I call DoWork I don’t see value is persist!

Its WCF setting that we are missing, WCF by default does not keep context for ever… we have to tell them to keep it alive per session, per call (default) or single. Per session requires some more extra efforts to get it working… let’s keep simple by using Single, it’s part of service behavior, lets add and see if that works…

Add attribute…

And let’s make call from client again..

Yes… we got it working J now as we make context mode to single, subsequent call of DoWork will return same result. That means its consider as a kind of Static

If we switch context mode to session then following code will behaves as expected

Hope this helps.

Understand the behavior of .NET function Math.Round

Hello All,

Recently I faced wired issue with Math.Round function. What is assumption for Math.Round function is “Rounds a double-precision floating-point value to the nearest integral value”

Lets examine this case. We are trying to Round 10.5 and 11.5

We are expecting result as 11 and 12. Let’s see the output

Unexpected!!! Does this means Math.Round having bug? Well the obvious answer is No. There is no bug in Math.Round function. Basically we are not using Math.Round function properly

Let’s check what documentation say about Math.Round function.

The document says, it will return the nearest EVEN number is returns. This is a reason why we got 10 instead of 11.

This is default behavior of Math.Round to return nearest even number, however we can change the behavior to get out expected result. There are few overloads provided by framework, we can use one which have control to return nearest even or odd which always be larger, in our case we always need large one. So lets use overload function of Math.Round

We are mentioning to give us a number which is away from Zero mean bigger one. This will give output as we are expecting.

 

There we go. So best practice to use Math.Round is always call overloads which is taking mode as an argument. There is two option for MidPointRounding enum, one is AwayFromZero and another is ToEven

I am sure lots of people is going to change their code after reading this blog post

Query to Find First and Last Day of Previous, Current and Next Month - SQL Server

Hello All,

This is normal requirement to find First and Last day of Month. I got one in which I have to find not only current month or given month but Previous and Next month as well.

Following query will gives start date and end date for previous, current and next month respectively. That is First Day of Previous Month, Last Day of Previous Month, First Day of Current Month, Last Day of Current Month, First Day of Next Month and Last Day of Next Month.

DECLARE @PreviousMonthFirstDay DATETIME
DECLARE @PreviousMonthLastDay DATETIME
DECLARE @CurrentMonthFirstDay DATETIME
DECLARE @CurrentMonthLastDay DATETIME
DECLARE @NextMonthFirstDay DATETIME
DECLARE @NextMonthLastDay DATETIME

DECLARE @CurrentDate AS DATETIME = CONVERT( DATETIME, CONVERT( DATE, GetDate() ) )

SELECT @CurrentMonthFirstDay = DATEADD(dd, -(DAY(@CurrentDAte)) + 1, @CurrentDate)
SELECT @CurrentMonthLastDay = DATEADD(d, -1, DATEADD(mm, 1, @CurrentMonthFirstDay))

SELECT @PreviousMonthFirstDay = DATEADD(m, -1, @CurrentMonthFirstDay)
SELECT @PreviousMonthLastDay = DATEADD(d, -1, @CurrentMonthFirstDay)

SELECT @NextMonthFirstDay = DATEADD(d, 1, @CurrentMonthLastDay)
SELECT @NextMonthLastDay = DATEADD(d, -1, DATEADD(mm, 1, @NextMonthFirstDay))

SELECT 
     @PreviousMonthFirstDay PreviousMonthFirstDay
    ,@PreviousMonthLastDay PreviousMonthLastDay
    ,@CurrentMonthFirstDay CurrentMonthFirstDay
    ,@CurrentMonthLastDay CurrentMonthLastDay
    ,@NextMonthFirstDay NextMonthFirstDay
    ,@NextMonthLastDay NextMonthLastDay 

Output as of 12-Dec-2012
You can make this more generic by replacing GetDate() with perticular date while setting up value of @CurrentDate

Operation is not valid due to the current state of the object

Hello All,

While working with web application, there may be case we got ‘Operation is not valid due to the current state of the object error’ or ‘The URL-encoded form data is not valid’ while doing postback

There may be other reason but one of the reason is form collection reaches its limit of maximum number of keys that it can hold a time. Means you have huge amount of data and you are trying to postback that data to server which end up with this error

‘Operation is not valid due to the current state of the object error’ or ‘The URL-encoded form data is not valid’

Microsoft has added this as security for Form can have 1000 items at a time, however thanks Microsoft also provides way to change this

To change this add following setting into your configuration file

<appSettings>
  <add key="aspnet:MaxHttpCollectionKeys" value="10000" />    
</appSettings>

In case you have issue with Jason data then you have to add following settings

<appSettings>
  <add key="aspnet:MaxJsonDeserializerMembers" value="10000" /></appSettings>

Hope this helps

Deleting Parent and its child record without setting ON CASCADE DELETE

Hello All,

Very recent I found requirement for removing parent record which is having tons of relation as they have foreign key constrains; you can’t delete them unless you have ON CASCADE DELETE

I found solution on Stack Overflow and base main article from sqlteam. I have modified procedure to fix some minor issue and here is the procedure which take table name and a query to filter row which we need to delete from table along with its reference.

-- ================================================
-- Expects the name of a table, and a conditional for selecting rows
-- within that table that you want deleted.
-- Produces SQL that, when run, deletes all table rows referencing the ones
-- you initially selected, cascading into any number of tables,
-- without the need for "ON DELETE CASCADE".
-- Does not appear to work with self-referencing tables, but it will
-- delete everything beneath them.
-- To make it easy on the server, put a "GO" statement between each line.
-- ================================================
CREATE PROCEDURE DeleteCascade (
     @BaseTableName VARCHAR(200)
    ,@BaseCriteria VARCHAR(1000)
)
AS BEGIN

    DECLARE @ToDelete TABLE 
    (
        Id INT IDENTITY(1, 1) PRIMARY KEY NOT NULL,
        Criteria VARCHAR(5000) NOT NULL,
        TableName VARCHAR(200) NOT NULL,
        Processed BIT NOT NULL,
        DeleteSql VARCHAR(5000)
    )

    SET NOCOUNT ON

    INSERT INTO @ToDelete (Criteria,TableName , Processed)
    VALUES (@BaseCriteria, @BaseTableName, 0)

    DECLARE @Id INT
    DECLARE @Criteria VARCHAR(5000)
    DECLARE @TableName VARCHAR(5000)

    WHILE EXISTS(SELECT 1 FROM @ToDelete WHERE Processed = 0) 
    BEGIN
    
        SELECT TOP 1 
            @Id = Id
            ,@Criteria = Criteria
            ,@TableName = TableName 
        FROM @ToDelete 
        WHERE Processed = 0 
        ORDER BY Id DESC

        INSERT INTO @ToDelete (Criteria, TableName, Processed)
        SELECT 
            ReferencingColumn.name + ' IN (SELECT [' + ReferencedColumn.name + '] FROM [' 
+ @TableName +'] WHERE ' + @Criteria + ')',
            ReferencingTable.name,0
        FROM sys.foreign_key_columns fk
        INNER JOIN sys.columns ReferencingColumn 
            ON fk.parent_object_id = ReferencingColumn.object_id 
            AND fk.parent_column_id = ReferencingColumn.column_id 
        INNER JOIN sys.columns ReferencedColumn 
            ON fk.referenced_object_id = ReferencedColumn.object_id 
            AND fk.referenced_column_id = ReferencedColumn.column_id 
        INNER JOIN sys.objects ReferencingTable 
            ON fk.parent_object_id = ReferencingTable.object_id 
        INNER JOIN sys.objects ReferencedTable 
            ON fk.referenced_object_id = ReferencedTable.object_id 
        INNER JOIN sys.objects constraint_object 
            ON fk.constraint_object_id = constraint_object.object_id
        WHERE ReferencedTable.name = @TableName
        AND ReferencingTable.name != ReferencedTable.name

        UPDATE @ToDelete 
        SET Processed = 1
        WHERE Id = @Id
        
    END
    
    SELECT 
        'PRINT ''Deleting from ' + TableName + '...''; DELETE FROM [' + TableName + '] WHERE ' 
+ Criteria 
    FROM @ToDelete 
    ORDER BY Id DESC
    
END

When you execute this, you will see list of DELETE statement, which you need to run.

Enumeration Types as Bit Flags

An enum is best practice to give internal constants to readable string format, example

It’s very handy to use string rather to remember int value and it also helps to maintain code if down the road we need to change integer value it wont be difficult. I am sure developer knows very well about how to use enum in their code.

The post is all about answering few question comes while development or requirement, How you pass multiple value by using enum? or How to assign multiple enum values to variable? or How can I store combination of enum values using single enum variable?

All question have single answer, to use enum as bit flags. In order to achieve this, you have to add new attribute Flags to your enum declaration. As these values are bit you can use bitwise operation which are AND, OR, XOR and NOT.

Let’s see useful example of Flag enum using normal coding and then we will see same thing using Flags.

In normal coding if I want to calculate discount for four country and more then one at same time, I rather create for methods and call four individual functions

OR I can add bool into signature for calculating particular discount.

Drawback of first method is you have to keep adding new functions if you introduce new country and in second you have to pass false to country which you don’t want to do calculation, so signature will get increase in case we have more countries

Now lets use Flag enumeration to avoid mention drawbacks.

This will how your new enum will look like

A new attribute called Flags is added and we have assigned constants in power or TWO, that is 1,2,4,8 and so on, so when we use in combination no one get overlap.

Lets go ahead and create CalculateDiscount function and use into our program.

So single function CalculateDiscount is responsible to calculate discount for four different country at a time. If I want to calculate discount for German and Canada, you can do that by passing both in single argument using ‘|’ operator, its bitwise OR operator. You can use ‘&’ bitwise AND operator to determine whether a specific flag is set or not.

Changing Physical Path of multiple Applications in IIS 7

Hello All,

Usually, we need functionality where we have more then one set of application configured in our machine, like QA environment and DEV environment. We don’t have way to keep two directory pointing to same location in single web site.

We can use backup feature for IIS 7 which helps to take backup as well as change directories of multiple applications at same time. First we are going to do backup IIS7

Go to your inetsvr directory for your system’s system32 directory from command prompt. Make sure you are using Administrator account, if not then open command prompt with “run as administrator”

 

Write following command in command prompt

appcmd add backup NAME_OF_BACKUP

I have created backup with name IISBackup, So we created backup of IIS including application pool, application, virtual directory etc. We will now change the physical path of more then one application and then restore backup back to IIS

Open backup folder in explorer.

Open that folder and edit applicationHost.config into notepad

In sites tag you can see your application with all details. Update physicalPath with your new path and save the file

Once you are done with this, go back to command prompt to restore our updated IIS settings, write following command, it will take few secs to set your new configurations.

appcmd restore backup NAME_OF_BACKUP

You are done!

So, we see how to backup and restore IIS, and how to change physical path of more then one applications.

Failed to Load Resource - Safari issue

Hello All,

Recently application stopped working on Safari with issue 'Failed to Load Resource'. The scenario is; the web page send AJAX-Request to an aspx page and show the output into html container. The issue occurred when the request comes form https and with Safari. Basically all WebKit based browser having same issue, like Chrome and Safari.

Post has been moved to beyondrelational.com

An error occurred while opening the queue:Access is denied - MSMQ exception

System.ServiceModel.MsmqException: An error occurred while opening the queue:Access is denied. (-1072824283, 0xc00e0025). The  message cannot be sent or received from the queue. Ensure that MSMQ is installed and running. Also ensure that the queue is available to open with the required access mode and authorization.

This post has been moved to beyondrelational.