Lesson 65 - Creating a New Instance of an Entity and Persisting it to the Database

Tutorial Series: Free C# Fundamentals via ASP.NET Web Apps

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Continuing on from where we left off in the previous lesson, we’ll now look at how to programmatically add new customers into the Customer table of the ACME database. We’ll accomplish this by taking in data via the Presentation layer and then storing it in the Persistence layer. This will demonstrate the typical mechanics of using the Entity Framework to insert a new Entity into a database. While this lesson touches upon the “create” and “read” part of a typical “CRUD” set of operations, you can extend the principals learned here towards understanding the “update” and “delete” operations as well.

Step 1: Create Controls in Default.aspx

The first thing we’ll do is add Form Controls to the Default.aspx page in order to gather data that the customer input on the Presentation layer. Once again, we'll be using the source code to create the Server Controls for our page:


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Step 2: Create a Method for Adding Customers

Back in CustomerRepository.cs of the Perisistence layer, we’ll first create a new method called AddCustomer() that returns void has an input parameter for a DTO.Customer. This method will create a new Customer (from Customer.cs), then fill it in with the values supplied from the DTO.Customer input argument:


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Step 3: Add the New Customer to the Database

Below the code we just wrote in the AddCustomer() method, we need to create a reference to the ACMEEntities database, adding the customer to it and then saving those changes with the SaveChanges() method:


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Without the use of the Add() method, the changes would never be committed to the actual database set of customers, just kept locally in memory. Similarly, the SaveChanges() method is used whenever you make a change to the database; whether that be creating a Customer, updating or deleting one.

Step 4: Validate the Data Before Committing it to the Database

It should be obvious that we will only want specific types of data to be entered into the database. To ensure this, we can add validation before the changes are saved to the database through the invocation of the SavedChanges() method. For example, you can add some validation at the top of the AddCustomer() method to protect against an empty field being submitted for the customer’s name by throwing an Exception before the changes are saved:


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You might then want to wrap the commit operation around a try/catch:


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Tip:

The example here is less than ideal. Normally, you would want to handle the Exception properly rather than re-throw it. Also, you would probably want to create a custom Exception that is handled in the Domain layer so as to avoid information bubbling up through layers that shouldn’t even be concerned with such details. The Domain layer, for example, shouldn't have any knowledge of an Entity Framework error, or even of the Entity Framework itself. The above approach will work in a pinch, however, just remember that you should strive to keep layers as separate as possible.


Step 5: Call AddCustomer() in the Domain Layer

Next, we’ll create an AddCustomer() method in CustomerManager.cs of the Domain layer that simply calls the AddCustomer() method we had just created in the Persistence layer. This may seem redundant, however, keeping the implementation details of adding customers in the Domain layer helps maintain Separation of Concerns. Go to CustomerManager.cs and add the method:


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You may be wondering if this step is necessary. After all, we're creating an entire method that simply calls a method in a different layer. The answer to this is yes and no. As we saw before, for a small application this is impractical. For a larger application with more requirements, however, this kind of functionality aids in maintainability throughout the lifecycle of the application.

Step 6: Store New Customer Data upon Button Click

Back in Default.aspx.cs we’ll add the following code to the okButton_Click event to create a new Customer and populate the properties with the information given by the user:


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Immediately below that code, we’ll then call the AddCustomer() method from the Domain layer and pass in the Customer data. Note that it’s a good habit to wrap method calls to outside layers around a try/catch, especially when that method is performing some sort of data access. Here we’ll simply display the error message if an Exception is caught:


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You should probably do the same to AddCustomer() in the CustomerManager.cs and actually perform some custom Exception Handling, including logging it:


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Finally, take the code responsible for displaying customer data – which had already been in the Page_Load() method - and put it into a private method in Default.aspx.cs:


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Call this method at the bottom of both Page_Load() and okButton_Click() to make sure the screen reflects the updated data when loading the page or clicking the OK button. When you run the application, enter customer data to see if everything is working correctly and successfully stores the data into the database:


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Related Articles in this Tutorial:

Lesson 1 - Series Introduction

Lesson 2 - Installing Visual Studio 2015

Lesson 3 - Building Your First Web App

Lesson 4 - Understanding What You Just Did

Lesson 5 - Working with Projects in Visual Studio

Lesson 6 - Simple Web Page Formatting in Visual Studio

Challenge 1

Solution 1

Lesson 7 - Variables and Data Types

Lesson 8 - Data Type Conversion

Lesson 9 - Arithmetic Operators

Lesson 10 - C# Syntax Basics

Challenge 2 - ChallengeSimpleCalculator

Solution - ChallengeSimpleCalculator

Lesson 11 - Conditional If Statements

Lesson 12 - The Conditional Ternary Operator

Challenge 3 - ChallengeConditionalRadioButton

Solution - Challenge Conditional RadioButton

Lesson 13 - Comparison and Logical Operators

Lesson 13 Challenge - First Papa Bob's Website

Solution - Challenge First Papa Bob's Website

Lesson 14 - Working with Dates and Times

Lesson 15 - Working With Spans of Time

Lesson 16 - Working with the Calendar Server Control

Challenge 4 - Challenge Days Between Dates

Solution - Challenge Days Between Dates

Lesson 17 - Page_Load and Page.IsPostBack

Lesson 18 - Setting a Break Point and Debugging

Lesson 19 - Formatting Strings

Challenge 5 - Challenge Epic Spies Assignment

Solution - Challenge Epic Spies Assignment

Lesson 20 - Maintaining State with ViewState

Lesson 21 - Storing Values in Arrays

Lesson 22 - Understanding Multidimensional Arrays

Lesson 23 - Changing the Length of an Array

Challenge 6 - Challenge Epic Spies Asset Tracker

Solution - Challenge Epic Spies Asset Tracker

Lesson 24 - Understanding Variable Scope

Lesson 25 - Code Blocks and Nested If Statements

Lesson 26 - Looping with the For Iteration Statement

Challenge 7 - Challenge For Xmen Battle Count

Solution - Challenge For Xmen Battle Count

Lesson 27 - Looping with the while() & do...while() Iteration Statements

Lesson 28 - Creating and Calling Simple Helper Methods

Lesson 29 - Creating Methods with Input Parameters

Lesson 30 - Returning Values from Methods

Lesson 31 - Creating Overloaded Methods

Lesson 32 - Creating Optional Parameters

Lesson 33 - Creating Names Parameters

Lesson 34 - Creating Methods with Output Parameters

Challenge 8 - Challenge Postal Calculator Helper Methods

Solution - Challenge Postal Calculator Helper Methods

Mega Challenge Casino

Solution - Mega Challenge Casino

Lesson 35 - Manipulating Strings

Challenge 9 - Phun With Strings

Solution - Challenge Phun With Strings

Lesson 36 - Introduction to Classes and Objects

Challenge - Hero Monster Classes Part 1

Solution - Hero Monster Classes Part 1

Challenge - Hero Monster Classes Part 2

Solution - Challenge Hero Monster Classes Part 2

Lesson 37 - Creating Class Files Creating Cohesive Classes and Code Navigation

Lesson 38 - Understanding Object References and Object Lifetime

Lesson 39 - Understanding the .NET Framework and Compilation

Lesson 40 - Namespaces and Using Directives

Lesson 41 - Creating Class Libraries and Adding References to Assemblies

Lesson 42 - Accessibility Modifiers, Fields and Properties

Lesson 43 - Creating Constructor Methods

Lesson 44 - Naming Conventions for Identifiers

Lesson 45 - Static vs Instance Members

Challenge 10 - Challenge Simple Darts

Solution - Challenge Simple Darts

Lesson 46 - Working with the List Collection

Lesson 47 - Object Initializers

Lesson 48 - Collection Initializers

Lesson 49 - Working with the Dictionary Collection

Lesson 50 - Looping with the foreach Iteration Statement

Lesson 51 - Implicitly-Typed Variables with the var Keyword

Challenge 11 - Challenge Student Courses

Solution - Challenge Student Courses

Mega Challenge War

Solution - Mega Challenge War

Lesson 52 - Creating GUIDs

Lesson 53 - Working with Enumerations

Lesson 54 - Understanding the switch() Statement

Lesson 55 - First Pass at the Separation of Concerns Principle

Lesson 56 - Understanding Exception Handling

Lesson 57 - Understanding Global Exception Handling

Lesson 58 - Understanding Custom Exceptions

Lesson 59 - Creating a Database in Visual Studio

Lesson 60 - Creating an Entity Data Model

Lesson 61 - Displaying the DbSet Result in an ASP.NET GridView

Lesson 62 - Implementing a Button Command in a GridView

Lesson 63 - Using a Tools-Centric Approach to Building a Database Application

Lesson 64 - Using a Maintenance-Driven Approach to Building a Database Application

Lesson 65 - Creating a New Instance of an Entity and Persisting it to the Database

Lesson 66 - Package Management with NuGet

Lesson 67 - NuGet No-Commit Workflow

Lesson 68 - Introduction the Twitter Bootstrap CSS Framework

Lesson 69 - Mapping Enum Types to Entity Properties in the Framework Designer

Lesson 70 - Deploying the App to Microsoft Azure Web Services Web Apps

Papa Bob's Mega Challenge

Papa Bob's Mega Solution Part 1 - Setting up the Solution

Papa Bob's Mega Solution Part 2 - Adding an Order to the Database

Papa Bob's Mega Solution Part 3 - Passing an Order from the Presentation Layer

Papa Bob's Mega Solution Part 4 - Creating the Order Form

Papa Bob's Mega Solution Part 5 - Adding Enums

Papa Bob's Mega Solution Part 6 - Creating an Order with Validation

Papa Bob's Mega Solution Part 7 - Calculating the Order Price

Papa Bob's Mega Solution Part 8 - Displaying the Price to the User

Papa Bob's Mega Solution Part 9 - Creating the Order Management Page


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