JavaScript : Error Handling With try/catch/finally

JavaScript error handling is a lot like other languages where you have the try/catch/finally  statement that you can used.  The basic premise is

try
{
     // try some codes here fingers crossed that nothing bad happens
}
catch(ex)
{
     // oops something bad happened, this is where it gets handled or I tell the user
}
finally
{
    // I don't care what happens I am going to execute and get paid
}

Here is the error handling in action:

JavaScript Objects Deep Dive: Preventing Errors When Accessing Object Properties

There are times when you will get an error when you tried to access a property in an object, sometimes you think a property exists in the object but it does not.  Let's use the product object from the previous blog post as an example.

        var product = new Object();

        product.name = "Chai";
        product.category = "Tea";
        product.country = "India";
        product.supplier = {
            name: "ACME Tea Of India",
            location: "New Delhi"
        };

Let's say another developer works on the project and he assumes that since there's a "country" property that there should be a "city" property.  If he tries to access the access the "city" property in the product object he will get an undefined, because the property does not exist.   If he types the following he will get the undefined message.

SQL: GROUP BY And HAVING

SQL GROUPING allows you to segregate data into groups so that you can work on it separately from the rest of the table records. Let's say you want to get the number of products in a category in the Northwind database Products table. You would write the following query:

 SELECT COUNT(*) NumberOfProductsByCategory
FROM Products
GROUP BY CategoryID

The query above gives you the following results:

Hour 4: ASP.NET Core : Create Our First Controller and View

In the previous post we have enabled MVC on our application.  Now we want to add our first MVC controller and view to test out verify that MVC is working.  We also have to tell ASP.NET Core what pattern to look for when looking for our controllers and views.

ASP.NET MVC: Add Area For Administrators

An ASP.NET MVC can get big, and it could be overwhelming.  Areas are a way to break up the application into smaller segments,  A perfect candidate for an Area is the Administrative features of the site because it has multiple pages, and functionalities.  So it is a good idea to segment off the Administration area to its own area (no pun intended).

ASP.NET Core: Add Logging To The NorthwindCafe Application

Logging is a good service to add as the application gets more complicated.  It will allow us to see what the error is when things goes wrong.

To add logging to our ASP.NET Core application follow the steps below:

1.  Open the Startup.cs file and add the logging service to the ConfigureServices method with the line

services.AddLogging();

So your ConfigureServices method should look like the following

        public void ConfigureServices(IServiceCollection services)
        {
            services.AddMvc();
            var connectionString = Startup.Configuration["Data:NorthwindContextConnection"];
            services.AddDbContext(options => options.UseSqlServer(connectionString));

            services.AddLogging();
        }

AngularJS SPA : Install MongoDB as a Windows Service

In the previous blog post we created a configuration file for our MongoDB database in this post we will install MongoDB as a Windows service so that we don't have to start the service in the command line every time we want to use it to save development time.

Here are the steps to install MongoDB:

1.  Open the command prompt as an "Administrator"

2.  Change the mongo-db-config.conf file to use absolute paths.  You can get the instructions on how to create a MongoDB configuration file in this blog post

            dbpath = C:\techjunkie\mongodb\db
            logpath = C:\techjunkie\mongodb\mongo-db-server.log
            verbose = vvvvv

if the folder dpath folder does not exists in Windows create the folder "db" inside the "mongodb" folder, else the service start will fail

End-to-End ASP.NET MVC : Create an ASP.NET MVC Empty Project

A lot of people think that you can only create one kind of ASP.NET MVC  project, the one with the sample application.  But the reality is that you can create an Empty ASP.NET MVC, you just need to do more work.  However, it is cleaner and you can add what you need, instead of having everything in place already like the default template.  So you might run into more errors with the empty project, but I think you will learn more about MVC than if you just have the default template.  Plus it's more streamline.  I always start with an empty project on my MVC projects.  In order to follow this tutorial you must have Visual Studio 2017 installed.

ASP.NET MVC : Upgrade ASP.NET MVC 4 to ASP.NET MVC 5 Using NuGet Part 2

In the previous blog we went over how to create a simple ASP.NET MVC 4 application.  In this blog we will go over the steps to upgrade our ASP.NET MVC 4 application to ASP.NET MVC 5 application.

Step-By-Step Instructions:

1. Open the "MyMVC4" project that you've created on the last blog
2. Right click on the project and select "Manage NuGet Packages..."

SQL : TRANSACTION

Transaction processing is a concept in SQL that allows you to execute a query or rollback the changes if something goes wrong.  A way of enforcing the data integrity of the database.  As such, you can only rollback INSERT, UPDATE, and DELETE.  Not that there's any use in rolling back a SELECT statement because there's no change in data.

The following is how you would wrap a transaction around a DELETE statement:

BEGIN TRANSACTION
DELETE Products WHERE ProductID = 87
COMMIT TRANSACTION

The above query will only execute if there are no errors, if there's an error the transaction will be rolled back. That's it, that's the whole concept of what a transaction is, if there are no errors then you should get the following message.

(1 row(s) affected)

If you are dealing with multiple statements then you can use the SAVE TRANSACTION, SAVE TRANSACTION allows you to create a placeholder so that you can rollback a transaction at a checkpoint.

SQL Server: The DELETE statement conflicted with the REFERENCE constraint "FK_Order_Details_Products". The conflict occurred in database "Northwind", table "dbo.Order Details", column 'ProductID'.

The DELETE statement conflicted with the REFERENCE constraint "FK_Order_Details_Products". The conflict occurred in database "Northwind", table "dbo.Order Details", column 'ProductID'. The statement has been terminated. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.Data.SqlClient.SqlException: The DELETE statement conflicted with the REFERENCE constraint "FK_Order_Details_Products". The conflict occurred in database "Northwind", table "dbo.Order Details", column 'ProductID'. The statement has been terminated. Source Error: An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below. Stack Trace: [SqlException (0x80131904): The DELETE statement conflicted with the REFERENCE constraint "FK_Order_Details_Products". The conflict occurred in database "Northwind", table "dbo.Order Details", column 'ProductID'. The statement has been terminated.] System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction) +1789294 System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction) +5340642 System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose) +244 System.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady) +1691 System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString) +275 System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async, Int32 timeout, Task& task, Boolean asyncWrite, SqlDataReader ds) +1421 System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, TaskCompletionSource`1 completion, Int32 timeout, Task& task, Boolean asyncWrite) +177 System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(TaskCompletionSource`1 completion, String methodName, Boolean sendToPipe, Int32 timeout, Boolean asyncWrite) +208 System.Data.SqlClient.SqlCommand.ExecuteNonQuery() +163 System.Web.UI.WebControls.SqlDataSourceView.ExecuteDbCommand(DbCommand command, DataSourceOperation operation) +378 System.Web.UI.WebControls.SqlDataSourceView.ExecuteDelete(IDictionary keys, IDictionary oldValues) +568 System.Web.UI.DataSourceView.Delete(IDictionary keys, IDictionary oldValues, DataSourceViewOperationCallback callback) +84 System.Web.UI.WebControls.GridView.HandleDelete(GridViewRow row, Int32 rowIndex) +930 System.Web.UI.WebControls.GridView.HandleEvent(EventArgs e, Boolean causesValidation, String validationGroup) +974 System.Web.UI.WebControls.GridView.RaisePostBackEvent(String eventArgument) +201 System.Web.UI.WebControls.GridView.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +13 System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13 System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +9703566 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1724 Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.34009

ASP.NET : WebForms UnobtrusiveValidationMode requires a ScriptResourceMapping for 'jquery'. Please add a ScriptResourceMapping named jquery(case-sensitive)

If you receive the WebForms UnobtrusiveValidationMode requires a ScriptResourceMapping for 'jquery' error, put the following lines of code in the Appliction_Start method in the Global.asax.cs file

        protected void Application_Start(object sender, EventArgs e)
        {
            string jqueryVersion = "1.8.0";

            System.Web.UI.ScriptManager.ScriptResourceMapping.AddDefinition("jquery", 
                                                new System.Web.UI.ScriptResourceDefinition
            {
                Path = "~/Scripts/jquery-" + jqueryVersion + ".min.js",
                DebugPath = "~/Scripts/jquery-" + jqueryVersion + ".js",
                CdnPath = "http://ajax.aspnetcdn.com/ajax/jQuery/jquery" + jqueryVersion + ".min.js",
                CdnDebugPath = "http://ajax.aspnetcdn.com/ajax/jQuery/jquery" + jqueryVersion + ".js",
                CdnSupportsSecureConnection = true,
                LoadSuccessExpression = "Window.jquery"
                
            });
        }

The above lines of code registers the jQuery library with the ScripManager. This will get rid of the error, you can do the same this with jQueryUI library.