Modern AspNetCore applications use the built-in web server kestrel,this server is usually bound to the localhost address using the ports 5000 and 5001 for http and https.
But what if you want to run 2 applications in the same server? then you have a problem because if you use the default ports one of the applications will not start correctly.
This can easily be solved by changing the default ports in your WebHostBuilder as shown below
The problem with the example above is that the URLs are hardcoded, so here is a better solution
public static IHostBuilder CreateHostBuilder(string[] args) =>
Host.CreateDefaultBuilder(args)
.ConfigureWebHostDefaults(webBuilder => {
var config = new ConfigurationBuilder()
.SetBasePath(Directory.GetCurrentDirectory())
.AddJsonFile("hosting.json", optional: true)
.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
.AddCommandLine(args)
.AddEnvironmentVariables()
.Build();
webBuilder.UseUrls(config["server.urls"]);
webBuilder.UseStartup<Startup>();
});
the example above uses a configuration builder to merge the appsettings.json and the hosting.json in a single configuration object, then with use the value of the property “server.urls” as base URL/port for our application
Sometime we want to reuse our Blazor components in another apps, the best way to do this is to create a razor library, this process of create a razor library is not different from create a normal class library to share code. There is only one exception, razor components might need to reference JavaScript or CSS files. This problem can be easily solve in 2 steps as shown below.
1) Create a class that inherits from TagHelperComponent,,this class should include the tags that you want to include in the html header section of your app
using Microsoft.AspNetCore.Html;
using Microsoft.AspNetCore.Razor.TagHelpers;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace MyBlazorApp
{
[HtmlTargetElement("head")]
public class MyTagHelper: TagHelperComponent
{
private string Tags=
@"
<!-- ZXingBlazor -->
<script src=""_content/ZXingBlazor/lib/barcodereader/zxing.js""></script>
<script src = ""_content/ZXingBlazor/lib/barcodereader/barcode.js"" ></ script >
< !--ZXingBlazor-- >
< !--Signature Pad -->
<script src = ""_content/Mobsites.Blazor.SignaturePad/bundle.js"" ></ script >
< link href=""_content/Mobsites.Blazor.SignaturePad/bundle.css"" rel=""stylesheet"" />
< link href=""_content/Ultra.PropertyEditors.Module.Blazor/js/signaturepropertyeditor.js""/>
<!-- Signature Pad -->
<!-- HTML Editor -->
<link href = ""//cdn.quilljs.com/1.3.6/quill.snow.css"" rel=""stylesheet"">
<link href = ""//cdn.quilljs.com/1.3.6/quill.bubble.css"" rel=""stylesheet"">
<script src = ""https://cdn.quilljs.com/1.3.6/quill.js"" ></ script >
<script src=""_content/Blazored.TextEditor/quill-blot-formatter.min.js""></script>
<script src = ""_content/Blazored.TextEditor/Blazored-BlazorQuill.js"" ></ script >
< !--HTML Editor -->
";
public override Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
{
if (string.Equals(context.TagName, "head", StringComparison.OrdinalIgnoreCase))
{
output.PostContent.AppendHtml(Tags).AppendLine();
}
return Task.CompletedTask;
}
}
}
*Note: to reference JavaScript or CSS from any razor library you can use the following syntax,please notice the doble quotes.
2) Create an extension method in the “Microsoft.Extensions.DependencyInjection” namespace so you can easily add your tag helper to the service collection
using Microsoft.AspNetCore.Razor.TagHelpers;
using Microsoft.Extensions.DependencyInjection;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace Microsoft.Extensions.DependencyInjection
{
public static class StartupExtensions
{
public static IServiceCollection AddMyHtmlTags(this IServiceCollection services)
{
services.AddTransient<ITagHelperComponent, MyTagHelper>();
return services;
}
}
}
Here is an example on how to use your new extension in your startup class
public void ConfigureServices(IServiceCollection services
{
services.AddMyHtmlTags();
}
The LogLevel section in the appsettings.json file does not affect the .NET Framework tracing mechanism, which is used by XPO to log the queries, still we have a few work arounds for a Netcore app
We can implement our own logger as shown here https://docs.devexpress.com/XPO/403928/best-practices/how-to-log-sql-queries#xpo-logger-net
We can set the value of the logging switch by reflection using the following snippet
Ok, so far, our synchronization framework is only implemented for an in-memory database that we use for testing purposes.
Now let’s implement a different use case, lets add synchronization functionality to an entity framework core DbContext.
As I explained before, the key part of synchronizing data using delta encoding is to be able to track the differences that happen to a data object, in this case, a relational database.
these are the task that we need to do to accomplish our goal
Find out how entity framework converts the changes that happen to the objects to SQL commands
Decide what information we need to track and save as a delta
Create the infrastructure to save deltas (IDeltaStore)
Create the infrastructure to process deltas (IDeltaProcessor)
Implement the synchronization node functionality in an Entity Framework DbContext(ISyncClientNode)
Create a test scenario
1 Find out how entity framework converts the changes that happen to the objects to SQL commands
In our companies (BitFrameworks & Xari) we have been working in data synchronization for a while, but all this work has been done in the XPO realm.
public abstract class ModificationCommandBatch
{
/// <summary>
/// The list of conceptual insert/update/delete <see cref="ModificationCommands" />s in the batch.
/// </summary>
public abstract IReadOnlyList<IReadOnlyModificationCommand> ModificationCommands { get; }
now let’s take look into the ModificationCommand https://github.com/dotnet/efcore/blob/main/src/EFCore.Relational/Update/ModificationCommand.cs this class provides all the information about the changes that will be converted into SQL commands, which means that if we serialize this object and save it as a delta we can then send it to another node and replicate the changes…VOILA!!!
So now we know where the changes that we need to keep track of are, now let’s try to understand how those changes are converted into SQL commands and then executed into the database.
2 Decide what information we need to track and save as a delta
Entity framework core uses dependency injection to be able to handle different database engines so the idea here is that there are a lot of small services that can be replaced in other to create a different implementation, for example, SQLite, SqlServer, Postgres, etc …
After a lot of digging, I found that the service that is in charge of generating the update commands (insert, update and delete) UpdateSqlGenerator
this class implements IUpdateSqlGenerator https://github.com/dotnet/efcore/blob/main/src/EFCore.Relational/Update/IUpdateSqlGenerator.cs and as you can see all methods receive a string builder and a ModificationCommand so this is the service in charge of translating the ModificationCommand into SQL commands and SQL commands are easy to serialize because they are just text, so this is what we are going to serialize and save as a delta
public interface IUpdateSqlGenerator
{
/// <summary>
/// Generates SQL that will obtain the next value in the given sequence.
/// </summary>
/// <param name="name">The name of the sequence.</param>
/// <param name="schema">The schema that contains the sequence, or <see langword="null" /> to use the default schema.</param>
/// <returns>The SQL.</returns>
string GenerateNextSequenceValueOperation(string name, string? schema);
/// <summary>
/// Generates a SQL fragment that will get the next value from the given sequence and appends it to
/// the full command being built by the given <see cref="StringBuilder" />.
/// </summary>
/// <param name="commandStringBuilder">The builder to which the SQL fragment should be appended.</param>
/// <param name="name">The name of the sequence.</param>
/// <param name="schema">The schema that contains the sequence, or <see langword="null" /> to use the default schema.</param>
void AppendNextSequenceValueOperation(
StringBuilder commandStringBuilder,
string name,
string? schema);
/// <summary>
/// Appends a SQL fragment for the start of a batch to
/// the full command being built by the given <see cref="StringBuilder" />.
/// </summary>
/// <param name="commandStringBuilder">The builder to which the SQL fragment should be appended.</param>
void AppendBatchHeader(StringBuilder commandStringBuilder);
/// <summary>
/// Appends a SQL command for deleting a row to the commands being built.
/// </summary>
/// <param name="commandStringBuilder">The builder to which the SQL should be appended.</param>
/// <param name="command">The command that represents the delete operation.</param>
/// <param name="commandPosition">The ordinal of this command in the batch.</param>
/// <returns>The <see cref="ResultSetMapping" /> for the command.</returns>
ResultSetMapping AppendDeleteOperation(
StringBuilder commandStringBuilder,
IReadOnlyModificationCommand command,
int commandPosition);
/// <summary>
/// Appends a SQL command for inserting a row to the commands being built.
/// </summary>
/// <param name="commandStringBuilder">The builder to which the SQL should be appended.</param>
/// <param name="command">The command that represents the delete operation.</param>
/// <param name="commandPosition">The ordinal of this command in the batch.</param>
/// <returns>The <see cref="ResultSetMapping" /> for the command.</returns>
ResultSetMapping AppendInsertOperation(
StringBuilder commandStringBuilder,
IReadOnlyModificationCommand command,
int commandPosition);
/// <summary>
/// Appends a SQL command for updating a row to the commands being built.
/// </summary>
/// <param name="commandStringBuilder">The builder to which the SQL should be appended.</param>
/// <param name="command">The command that represents the delete operation.</param>
/// <param name="commandPosition">The ordinal of this command in the batch.</param>
/// <returns>The <see cref="ResultSetMapping" /> for the command.</returns>
ResultSetMapping AppendUpdateOperation(
StringBuilder commandStringBuilder,
IReadOnlyModificationCommand command,
int commandPosition);
}
3 Create the infrastructure to save deltas (Implementing IDeltaStore)
Now is time to create a delta store, this is an easy one since we only need to inherit from our delta store base and save the information in an entity framework DbContext, so here is the implementation
4 Create the infrastructure to process deltas (implementing IDeltaProcessor)
So far, we know what we need to store in the deltas which basically is SQL commands and their parameters so it means to process those SQL Commands our delta processor needs to create a database connection and execute SQL commands
public EFDeltaProcessor(DbContext dBContext)
{
_dBContext = dBContext;
}
public EFDeltaProcessor(string connectionstring, string DbEngineAlias, string ProviderInvariantName)
{
this.CurrentDbEngine = DbEngineAlias;
this.connectionString = connectionstring;
try
{
factory = DbProviderFactories.GetFactory(ProviderInvariantName);
}
catch (Exception ex)
{
Debug.WriteLine(ex.Message);
throw new Exception("There was a problem creating the database connection using DbProviderFactories.GetFactory. Please your make sure the DbProviderFactory for your database is registered https://docs.microsoft.com/en-us/dotnet/api/system.data.common.dbproviderfactories.registerfactory?view=net-5.0", ex);
}
//TODO check provider registration later
//DbProviderFactories.RegisterFactory("Microsoft.Data.SqlClient", SqlClientFactory.Instance);
}
there are a few things to notice in that class, first, it has 2 constructors because we need 2 different ways to create the connection to the database, one using the entity framework DbContext and one using ADO.NET DbProviderFactory
All the magic happens in the ProcessDeltas method, this method is in charge of, extract the content of the deltas and transforming them into SQL commands and parameters, and then executing the command.
please notice that the content of each delta is an instance of ModificationCommandData
which is a class that allows us to store multiple SQL commands (for different database engines) and their parameters
5 Implement the synchronization node functionality in an Entity Framework DbContext(ISyncClientNode)
At the moment we are able to produce and process deltas for entity framework relational, so the next step is to implement the functionality of synchronization client node by implementing the following interface
I’m not going to show the implementation of the server since that implementation is generic and uses the same delta store and delta processor that we created at the beginning of this article. for more information check the following links
So far, all our test exists inside the same process, so they communicate through variables, in real-life scenarios nodes won’t exist in the same process and most of the time not even in the same location.
The easiest and most standard way to implement client-server communication in the dotnet world is a rest API, so let’s define an API client and a server service, lets start with the API client
public class SyncFrameworkHttpClient : ISyncFrameworkClient
{
HttpClient _httpClient;
public string DeltaStoreId { get; }
public SyncFrameworkHttpClient(HttpClient httpClient,string NodeId)
{
this.DeltaStoreId = NodeId;
_httpClient = httpClient;
_httpClient.DefaultRequestHeaders.Add("NodeId", NodeId);
this.DeltaStoreId = NodeId;
}
public SyncFrameworkHttpClient(string BaseAddress, string DeltaStoreId):this(new HttpClient() { BaseAddress=new Uri(BaseAddress)},DeltaStoreId)
{
}
public virtual async Task PushAsync(IEnumerable<IDelta> Deltas, CancellationToken cancellationToken = default)
{
try
{
List<Delta> toserialzie = new List<Delta>();
foreach (IDelta delta in Deltas)
{
toserialzie.Add(new Delta(delta));
}
cancellationToken.ThrowIfCancellationRequested();
DataContractJsonSerializer js = new DataContractJsonSerializer(typeof(List<Delta>));
MemoryStream msObj = new MemoryStream();
js.WriteObject(msObj, toserialzie);
msObj.Position = 0;
StreamReader sr = new StreamReader(msObj);
string jsonDeltas = sr.ReadToEnd();
var data = new StringContent(jsonDeltas, Encoding.UTF8, "application/json");
await _httpClient.PostAsync("/Sync/Push", data, cancellationToken).ConfigureAwait(false);
}
catch (Exception ex)
{
var message = ex.Message;
throw;
}
}
public virtual async Task<List<Delta>> FetchAsync(Guid startindex, string identity, CancellationToken cancellationToken = default)
{
var QueryParams = new Dictionary<string, string>();
QueryParams.Add(nameof(startindex), startindex.ToString());
QueryParams.Add(nameof(identity), identity);
cancellationToken.ThrowIfCancellationRequested();
var query = HttpUtility.ParseQueryString("");
foreach (KeyValuePair<string, string> CurrentParam in QueryParams)
{
query[CurrentParam.Key] = CurrentParam.Value;
}
var reponse = await _httpClient.GetStringAsync($"/Sync/Fetch?{query.ToString()}").ConfigureAwait(false);
using (var ms = new MemoryStream(Encoding.Unicode.GetBytes(reponse)))
{
DataContractJsonSerializer deserializer = new DataContractJsonSerializer(typeof(List<Delta>));
List<Delta> Deltas = (List<Delta>)deserializer.ReadObject(ms);
return Deltas;
}
//List<Delta> Deltas = JsonConvert.DeserializeObject<List<Delta>>(reponse);
return null;
}
}
it’s an implementation of the ISyncFrameworkClient interface using HTTP communication
Fetch: uses an HTTP get request
Push: uses an HTTP post request
Also, the “nodeid” header is added to the request, you will understand why when we implement the server part.
Now that we have defined the contract for the client and also provided the base implementation using an HTTP client, its time to define what a client node is, please take a look at the code below
public static class ISyncClientNodeExtensions
{
public static async Task<List<Delta>> FetchAsync(this ISyncClientNode instance, CancellationToken cancellationToken = default)
{
cancellationToken.ThrowIfCancellationRequested();
var LastDetalIndex = await instance.DeltaStore.GetLastProcessedDeltaAsync(cancellationToken).ConfigureAwait(false);
return await instance.SyncFrameworkClient.FetchAsync(LastDetalIndex, instance.Identity, cancellationToken).ConfigureAwait(false);
}
public static async Task PullAsync(this ISyncClientNode instance, CancellationToken cancellationToken = default)
{
cancellationToken.ThrowIfCancellationRequested();
var Deltas = await instance.FetchAsync(cancellationToken).ConfigureAwait(false);
if (Deltas.Any())
{
await instance.DeltaProcessor.ProcessDeltasAsync(Deltas, cancellationToken).ConfigureAwait(false);
Guid index = Deltas.Max(d => d.Index);
await instance.DeltaStore.SetLastProcessedDeltaAsync(index, cancellationToken).ConfigureAwait(false);
}
}
public static async Task PushAsync(this ISyncClientNode instance, CancellationToken cancellationToken = default)
{
cancellationToken.ThrowIfCancellationRequested();
var LastPushedDelta = await instance.DeltaStore.GetLastPushedDeltaAsync(cancellationToken).ConfigureAwait(false);
var Deltas = await instance.DeltaStore.GetDeltasAsync(LastPushedDelta,cancellationToken).ConfigureAwait(false);
if (Deltas.Any())
{
var Max = Deltas.Max(d => d.Index);
await instance.SyncFrameworkClient.PushAsync(Deltas, cancellationToken).ConfigureAwait(false);
await instance.DeltaStore.SetLastPushedDeltaAsync(Max,cancellationToken).ConfigureAwait(false);
}
}
}
so, this is how the SyncClientNode is structured
Let’s move to the server-side now, here the idea is to be able to host multiple delta store and delta processors and also to be able to introduce custom logic either saving the deltas into the delta store or processing the deltas into a data object
