Sep 8

Written by: Michael Washington
9/8/2019 10:29 AM  RssIcon

The primary benefit we have when using server-side Blazor is that we do not have to make web http calls from the client code to the server code. This reduces the code we need to write and eliminates many security concerns.

In this article, we will demonstrate how a list of Weather forecasts can be added to the database by each user. A user will only have the ability to see their own forecasts.

 

Use SQL Server

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The new project template in Visual Studio will allow you to create a database using SQL Server Express LocalDB. However, it can be problematic to install and configure. Using the free SQL Server 2017 Developer server (or the full SQL Server) is recommended.

Download and install SQL Server 2017 Developer Edition from the following link:

https://www.microsoft.com/en-us/sql-server/sql-server-downloads

 

Create The Blazor Application

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Open Visual Studio.

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Select Create a new Project.

 

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Select Blazor Server App and click Next.

 

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Give it a name and click Create.

 

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Select Blazor Server App.

 

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Click the Change link under Authentication.

 

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Select Individual User Accounts and Store user accounts in-app.

 

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Click Create.

 

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The project will be created.

 

Create The Database

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Open the SQL Server Object Explorer.

 

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Add a connection to your local database server if you don’t already have it in the SQL Server list.

For this tutorial, we do not want to use the SQL Express server on (localdb) that you may already see in the list.

 

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You will specify just the server and Connect.

 

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Expand the tree under the local SQL server, right-click on the Databases folder and select Add New Database.

 

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Give the database a name and press Enter.

The database will be created.

Click on the Database node.

 

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Open the Properties window if it is not already opened.

The properties for the database will display.

Copy the Connection string for the database.

 

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Open the appsettings.json file.

 

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Paste in the connection string for the DefaultConnection and save the file.

 

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Hit F5 to run the application.

 

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The application will open in your web browser.

Click the Register link.

 

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Enter the information to create a new account.

Click the Register button.

 

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Because this is the first time the database is being used, you will see a message asking you to run the migration scripts that will create the database objects needed to support the user membership code.

Click the Apply Migrations button.

 

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After the message changes to Migrations Applied, refresh the page in the web browser.

 

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You will now be logged into the application.

You can click around the application and see that it works.

 

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The Fetch data page currently shows random data. We will alter the application to allow us to add, update, and delete this data in the database.

Close the web browser to stop the application.

 

Create The Database

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When we return to Visual Studio, and the SQL Server Object Explorer window, we see the tables that the migration scripts added.

 

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Right-click on the Tables node and select Add New Table.

 

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Paste the following script in the T-SQL window and then click the Update button:

 

CREATE TABLE [dbo].[WeatherForecast] (
    [Id]           INT           IDENTITY (1, 1) NOT NULL,
    [Date]         DATETIME      NULL,
    [TemperatureC] INT           NULL,
    [TemperatureF] INT           NULL,
    [Summary]      NVARCHAR (50) NULL,
    [UserName]     NVARCHAR (50) NULL,
    PRIMARY KEY CLUSTERED ([Id] ASC)
);

 

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The script will prepare.

Click the Update Database button.

 

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Back in the Server Explorer window, right-click on Tables and select Refresh.

 

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The WeatherForecast table will display.

Right-click on the table and select Show Table Data.

 

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We will enter some sample data so that we will be able to test the data connection in the next steps.

Set the UserName field to the username of the user that we registered an account for earlier.

 

Create The Data Context

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If you do not already have it installed, install EF Core Power Tools from:

https://marketplace.visualstudio.com/items?itemName=ErikEJ.EFCorePowerTools

 

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(Note: Before installing, close Visual Studio)

(Note: Please give this project a 5 star review on marketplace.visualstudio.com!)

 

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Right-click on the project node in the Solution Explorer and select EF Core Power Tools then Reverse Engineer.

 

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Click the Add button.

 

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Connect to the database.

 

 

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Select the database connection in the dropdown and click OK.

 

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Select the WeatherForecast table and click OK.

 

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Set the values and click OK.

 

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In the Solution Explorer, you will see the Data Context has been created.

Click the OK button to close the popup.

 

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Open the Startup.cs file.

Add the following code to the ConfigureServices section:

 

    // Read the connection string from the appsettings.json file
    // Set the database connection for the EndtoEndContext
    services.AddDbContext<EndToEndDB.Data.EndToEnd.EndtoEndContext>(options =>
    options.UseSqlServer(
        Configuration.GetConnectionString("DefaultConnection")));

 

Also, change this line:

 

            services.AddSingleton<WeatherForecastService>();

 

to this:

 

            // Scoped creates an instance for each user
            services.AddScoped<WeatherForecastService>();

 

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Save the file.

Select Build, then Rebuild Solution.

 

Read From The Database

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Delete the Data/WeatherForecast.cs file in the project.

We will use the Data/EndToEnd/WeatherForcast.cs class file created by the EF Core Tools instead.

 

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Open the WeatherForecastService.cs file.

Replace all the code with the following code:

 

using EndToEndDB.Data.EndToEnd;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
namespace EndToEnd.Data
{
    public class WeatherForecastService
    {
        private readonly EndtoEndContext _context;
        public WeatherForecastService(EndtoEndContext context)
        {
            _context = context;
        }
        public Task<List<WeatherForecast>>
            GetForecastAsync(string strCurrentUser)
        {
            List<WeatherForecast> colWeatherForcasts =
                new List<WeatherForecast>();
            // Get Weather Forecasts  
            colWeatherForcasts =
                (from weatherForecast in _context.WeatherForecast
                     // only get entries for the current logged in user
                     where weatherForecast.UserName == strCurrentUser
                 select weatherForecast).ToList();
            return Task.FromResult(colWeatherForcasts);
        }
    }
}

 

This line:

 

var context = new EndtoEndContext()

 

Connects to the database using the datacontext we created with the EF Core tools.

 

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Finally, open the FetchData.razor file.

Replace all the code with the following code:

 

@page "/fetchdata"
@using EndToEnd.Data
@using EndToEndDB.Data.EndToEnd
@inject AuthenticationStateProvider AuthenticationStateProvider
@*
    Using OwningComponentBase ensures that the service and related services
    that share its scope are disposed with the component.
    Otherwise DbContext in ForecastService will live for the life of the
    connection, which may be problematic if clients stay
    connected for a long time.
    We access WeatherForecastService using @Service
*@
@inherits OwningComponentBase<WeatherForecastService>
<h1>Weather forecast</h1>
<!-- AuthorizeView allows us to only show sections of the page -->
<!-- based on the security on the current user -->
<AuthorizeView>
    <!-- Show this section if the user is logged in -->
    <Authorized>
        <h4>Hello, @context.User.Identity.Name!</h4>
        @if (forecasts == null)
        {
            <!-- Show this if the current user has no data... yet... -->
            <p><em>Loading...</em></p>
        }
        else
        {
            <!-- Show the forecasts for the current user -->
            <table class="table">
                <thead>
                    <tr>
                        <th>Date</th>
                        <th>Temp. (C)</th>
                        <th>Temp. (F)</th>
                        <th>Summary</th>
                    </tr>
                </thead>
                <tbody>
                    @foreach (var forecast in forecasts)
                    {
                        <tr>
                            <td>@forecast.Date.Value.ToShortDateString()</td>
                            <td>@forecast.TemperatureC</td>
                            <td>@forecast.TemperatureF</td>
                            <td>@forecast.Summary</td>
                        </tr>
                    }
                </tbody>
            </table>
        }
    </Authorized>
    <!-- Show this section if the user is not logged in -->
    <NotAuthorized>
        <p>You're not signed in.</p>
    </NotAuthorized>
</AuthorizeView>
@code {
    // AuthenticationState is available as a CascadingParameter
    [CascadingParameter]
    private Task<AuthenticationState> authenticationStateTask { get; set; }
    List<WeatherForecast> forecasts;
    protected override async Task OnInitializedAsync()
    {
        // Get the current user
        var user = (await authenticationStateTask).User;
        // Get the forecasts for the current user
        // We access WeatherForecastService using @Service
        forecasts = await @Service.GetForecastAsync(user.Identity.Name);
    }
}

 

This code simply calls the GetForecastAsync method we created in the previous step, passing the username of the currently logged in user.

In a normal web application we would have to make a http web call from this client code to the code that connects to the database.

With server-side Blazor we don’t have to do that, yet the call is still secure because the pages are rendered on the server.

 

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Build and run the project.

If we are not logged in, and we go to the Fetch data page, we will see a message indicating we are not signed in.

 

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Click the Login button.

 

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Log in as the user we created data for earlier.

 

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After you are logged in, switch to the Fetch data page and you will see the data for the user we entered earlier.

 

Inserting Data Into The Database

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Open the WeatherForecastService.cs file and add the following method:

 

        public Task<WeatherForecast>
            CreateForecastAsync(WeatherForecast objWeatherForecast)
        {
            _context.WeatherForecast.Add(objWeatherForecast);
            _context.SaveChanges();
            return Task.FromResult(objWeatherForecast);
        }

 

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Open the FetchData.razor file.

Add the following HTML markup directly under the existing table element:

 

            <p>
                <!-- Add a new forecast -->
                <button class="btn btn-primary"
                        @onclick="AddNewForecast">
                    Add New Forecast
                </button>
            </p>

 

This adds a button to allow a new forecast to be added.

Add the following code below the previous code:

 

   @if (ShowPopup)
            {
                <!-- This is the popup to create or edit a forecast -->
                <div class="modal" tabindex="-1" style="display:block" role="dialog">
                    <div class="modal-dialog">
                        <div class="modal-content">
                            <div class="modal-header">
                                <h3 class="modal-title">Edit Forecast</h3>
                                <!-- Button to close the popup -->
                                <button type="button" class="close"
                                        @onclick="ClosePopup">
                                    <span aria-hidden="true">X</span>
                                </button>
                            </div>
                            <!-- Edit form for the current forecast -->
                            <div class="modal-body">
                                <input class="form-control" type="text"
                                       placeholder="Celsius forecast"
                                       @bind="objWeatherForecast.TemperatureC" />
                                <input class="form-control" type="text"
                                       placeholder="Fahrenheit forecast"
                                       @bind="objWeatherForecast.TemperatureF" />
                                <input class="form-control" type="text"
                                       placeholder="Summary"
                                       @bind="objWeatherForecast.Summary" />
                                <br />
                                <!-- Button to save the forecast -->
                                <button class="btn btn-primary"
                                        @onclick="SaveForecast">
                                    Save
                                </button>
                            </div>
                        </div>
                    </div>
                </div>
            }

 

This adds a form (that will be displayed a popup because the class for the DIV is modal), that allows the user to enter (and later edit) data for a forecast.

We do not need JavaScript to make this popup show. We only need to wrap this code with:

 

            @if (ShowPopup)
            {
                ...
            }

 

When the ShowPopup value is true the popup will show. When the value is false, the popup will disappear.

Add the following code to the @code section:

 

    WeatherForecast objWeatherForecast = new WeatherForecast();
    bool ShowPopup = false;
    void ClosePopup()
    {
        // Close the Popup
        ShowPopup = false;
    }
    void AddNewForecast()
    {
        // Make new forecast
        objWeatherForecast = new WeatherForecast();
        // Set Id to 0 so we know it is a new record
        objWeatherForecast.Id = 0;
        // Open the Popup
        ShowPopup = true;
    }
    async Task SaveForecast()
    {
        // Close the Popup
        ShowPopup = false;
        // Get the current user
        var user = (await authenticationStateTask).User;
        // A new forecast will have the Id set to 0
        if (objWeatherForecast.Id == 0)
        {
            // Create new forecast
            WeatherForecast objNewWeatherForecast = new WeatherForecast();
            objNewWeatherForecast.Date = System.DateTime.Now;
            objNewWeatherForecast.Summary = objWeatherForecast.Summary;
            objNewWeatherForecast.TemperatureC =
            Convert.ToInt32(objWeatherForecast.TemperatureC);
            objNewWeatherForecast.TemperatureF =
            Convert.ToInt32(objWeatherForecast.TemperatureF);
            objNewWeatherForecast.UserName = user.Identity.Name;
            // Save the result
            var result =
            @Service.CreateForecastAsync(objNewWeatherForecast);
        }
        else
        {
            // This is an update
        }
        // Get the forecasts for the current user
        forecasts =
        await @Service.GetForecastAsync(user.Identity.Name);
    }

 

 

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When you run the project, you can click the Add New Forecast button to add an entry.

 

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The form only requires a Fahrenheit, Celsius, and a summary, because the other values (date and username), will be set by the code.

 

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After clicking the Save button, the entry is saved to the database and displayed.

 

Updating The Data

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Open the WeatherForecastService.cs file and add the following method:

 

     public Task<bool>
            UpdateForecastAsync(WeatherForecast objWeatherForecast)
        {
            var ExistingWeatherForecast =
                _context.WeatherForecast
                .Where(x => x.Id == objWeatherForecast.Id)
                .FirstOrDefault();
            if (ExistingWeatherForecast != null)
            {
                ExistingWeatherForecast.Date =
                    objWeatherForecast.Date;
                ExistingWeatherForecast.Summary =
                    objWeatherForecast.Summary;
                ExistingWeatherForecast.TemperatureC =
                    objWeatherForecast.TemperatureC;
                ExistingWeatherForecast.TemperatureF =
                    objWeatherForecast.TemperatureF;
                _context.SaveChanges();
            }
            else
            {
                return Task.FromResult(false);
            }
            return Task.FromResult(true);
        }

 

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Open the FetchData.razor file.

Replace the existing table element with the following markup that adds an edit button in the last column (that calls the EditForecast method we will add in the next step):

 

           <table class="table">
                <thead>
                    <tr>
                        <th>Date</th>
                        <th>Temp. (C)</th>
                        <th>Temp. (F)</th>
                        <th>Summary</th>
                        <th></th>
                    </tr>
                </thead>
                <tbody>
                    @foreach (var forecast in forecasts)
                    {
                        <tr>
                            <td>@forecast.Date.Value.ToShortDateString()</td>
                            <td>@forecast.TemperatureC</td>
                            <td>@forecast.TemperatureF</td>
                            <td>@forecast.Summary</td>
                            <td>
                                <!-- Edit the current forecast -->
                                <button class="btn btn-primary"
                                        @onclick="(() => EditForecast(forecast))">
                                    Edit
                                </button>
                            </td>
                        </tr>
                    }
                </tbody>
            </table>

 

Add the following code to the @code section:

 

    void EditForecast(WeatherForecast weatherForecast)
    {
        // Set the selected forecast
        // as the current forecast
        objWeatherForecast = weatherForecast;
        // Open the Popup
        ShowPopup = true;
    }

 

This sets the current record to the objWeatherForecast object that the popup is bound to, and opens the popup.

Finally, change the existing SaveForecast method to the following:

 

    async Task SaveForecast()
    {
        // Close the Popup
        ShowPopup = false;
        // Get the current user
        var user = (await authenticationStateTask).User;
        // A new forecast will have the Id set to 0
        if (objWeatherForecast.Id == 0)
        {
            // Create new forecast
            WeatherForecast objNewWeatherForecast = new WeatherForecast();
            objNewWeatherForecast.Date = System.DateTime.Now;
            objNewWeatherForecast.Summary = objWeatherForecast.Summary;
            objNewWeatherForecast.TemperatureC =
            Convert.ToInt32(objWeatherForecast.TemperatureC);
            objNewWeatherForecast.TemperatureF =
            Convert.ToInt32(objWeatherForecast.TemperatureF);
            objNewWeatherForecast.UserName = user.Identity.Name;
            // Save the result
            var result =
            @Service.CreateForecastAsync(objNewWeatherForecast);
        }
        else
        {
            // This is an update
            var result =
            @Service.UpdateForecastAsync(objWeatherForecast);
        }
        // Get the forecasts for the current user
        forecasts =
        await @Service.GetForecastAsync(user.Identity.Name);
    }

 

This simply adds one line:

 

            // This is an update
            var result =
            @Service.UpdateForecastAsync(objWeatherForecast);

 

To the existing method to handle an update rather than an insert.

 

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When we run the application, we now have an Edit button to edit the existing record.

 

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The existing record will display in the popup, allowing us to edit the data and save it.

 

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The updated record is then displayed in the table.

 

Deleting The Data

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Open the WeatherForecastService.cs file and add the following method:

 

        public Task<bool>
            DeleteForecastAsync(WeatherForecast objWeatherForecast)
        {
            var ExistingWeatherForecast =
                _context.WeatherForecast
                .Where(x => x.Id == objWeatherForecast.Id)
                .FirstOrDefault();
            if (ExistingWeatherForecast != null)
            {
                _context.WeatherForecast.Remove(ExistingWeatherForecast);
                _context.SaveChanges();
            }
            else
            {
                return Task.FromResult(false);
            }
            return Task.FromResult(true);
        }

 

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Open the FetchData.razor file.

Add code markup for a Delete button under the code markup for the current Save button in the popup:

 

            <!-- Only show delete button if not a new record -->
            @if (objWeatherForecast.Id > 0)
            {
                <!-- Button to delete the forecast -->
                <button class="btn btn-primary"
                        @onclick="DeleteForecast">
                    Delete
                </button>
            }

 

Add the following code to the @code section:

 

    async Task DeleteForecast()
    {
        // Close the Popup
        ShowPopup = false;
        // Get the current user
        var user = (await authenticationStateTask).User;
        // Delete the forecast
        var result = @Service.DeleteForecastAsync(objWeatherForecast);
        // Get the forecasts for the current user
        forecasts =
        await @Service.GetForecastAsync(user.Identity.Name);
    }

 

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When we run the code and click the Edit button…

 

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… we now see a Delete button that will delete the record.

 

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However, when we click the Add New Forecast button that opens the same popup

 

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The delete button does not display (because there is no record to delete at this point).

 

Links

Blazor.net

ASP.NET Core Blazor authentication and authorization

EF Core Power Tools

OwningComponentBase (background)

 

Download

The project is available at http://BlazorHelpWebsite.com/Downloads.aspx

You must have Visual Studio 2019 Preview Edition (or higher) installed to run the code.

Tags: Blazor
Categories:

16 comment(s) so far...


Gravatar

Re: Creating A Step-By-Step End-To-End Database Server-Side Blazor Application

You demos are always so easy for me to follow and I love your enthusiasm for Blazor. I look forward to following your journy with this one Michael!

By Paul Pitchford on   7/1/2019 4:00 AM
Gravatar

Re: Creating A Step-By-Step End-To-End Database Server-Side Blazor Application

@Paul Pitchford - Thank You! Yeah I'm "all in" on this one :)

By Michael Washington on   7/1/2019 4:01 AM
Gravatar

Re: Creating A Step-By-Step End-To-End Database Server-Side Blazor Application

Great article! Question: What process do you take when you need to make changes to the database? Modifying existing tables, adding new ones, creating FK? Do you make the change to the db and then reverse engineer again or is there something else you recommend? Thanks

By Dave on   7/1/2019 9:47 AM
Gravatar

Re: Creating A Step-By-Step End-To-End Database Server-Side Blazor Application

@Dave - I manually update the database then the EF Core Tools allows you to simply re-run the process I outline and it will update the DataContext code. So yes, I: "change to the db and then reverse engineer again".

By Michael Washington on   7/1/2019 9:49 AM
Gravatar

Re: Creating A Step-By-Step End-To-End Database Server-Side Blazor Application

Great article!
Thank You!

You forget to declare "objWeatherForecast"

WeatherForecast objWeatherForecast;

By azoz on   7/2/2019 3:48 AM
Gravatar

Re: Creating A Step-By-Step End-To-End Database Server-Side Blazor Application

@azoz - Thank you for letting me know! I updated the article. I also provide the full code on the download page.

By Michael Washington on   7/2/2019 3:55 AM
Gravatar

Re: Creating A Step-By-Step End-To-End Database Server-Side Blazor Application

This article helped me to learn Blazor! Thank you so much!

Today I upgraded Visual Studio 2019 preview and I ended up with this error in FetchData.razor No suitable method to override. Can you help me to solve this error?

protected override async Task OnInitAsync()
{
// Get the current user
var user = (await authenticationStateTask).User;

// Get the forecasts for the current user
forecasts =
await ForecastService.GetForecastAsync(user.Identity.Name);
}

By Ivan Krsmanović on   8/14/2019 8:37 AM
Gravatar

Re: Creating A Step-By-Step End-To-End Database Server-Side Blazor Application

@Ivan Krsmanović - Change OnInitAsync to OnInitializedAsync see: https://devblogs.microsoft.com/aspnet/asp-net-core-and-blazor-updates-in-net-core-3-0-preview-8/

By Michael Washington on   8/14/2019 8:38 AM
Gravatar

Re: Creating A Step-By-Step End-To-End Database Server-Side Blazor Application

Great tutorial!! Really easy to follow.

By Richard T Waddell on   8/26/2019 6:28 AM
Gravatar

Re: Creating A Step-By-Step End-To-End Database Server-Side Blazor Application

When close the chrome application not auto logged out

By Novfal on   8/29/2019 4:59 AM
Gravatar

Re: Creating A Step-By-Step End-To-End Database Server-Side Blazor Application

@Noval - If you feel you have encountered a bug with Blazor, you can file an issue here: https://github.com/aspnet/AspNetCore/issues

By Michael Washington on   8/29/2019 5:07 AM
Gravatar

Re: Creating A Step-By-Step End-To-End Database Server-Side Blazor Application

Good Example, thank you.

By Fahmi on   9/3/2019 5:46 AM
Gravatar

Re: Creating A Step-By-Step End-To-End Database Server-Side Blazor Application

So good to see Michael doing Blazor tutorials. Those of us who learned Visual Studio Lightswitch (may it RIP) from him know there's no one better for getting you up to speed on a new technology.

Just purchased his book, I strongly suggest anyone else interested in Blazor does the same, stat.

By LarryQ on   9/9/2019 10:50 AM
Gravatar

Re: Creating A Step-By-Step End-To-End Database Server-Side Blazor Application

@LarryQ - Thanks for the support!

By Michael Washington on   9/9/2019 10:50 AM
Gravatar

Re: Creating A Step-By-Step End-To-End Database Server-Side Blazor Application

Hello Michael! This tutorial helped me a lot. Can you please show us how to print from Blazor or create PDF documents?

If you have this topic covered in your book I'll be happy to purchase it?!

Once again, thank you so much for great tutorials.

By Ivan Krsmanović on   9/15/2019 5:56 AM
Gravatar

Re: Creating A Step-By-Step End-To-End Database Server-Side Blazor Application

@Ivan Krsmanović - Yes it is in the book.

By Michael Washington on   9/15/2019 5:56 AM

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