EntityFrameworkDiffLog by HodStudio

An easy way to create entity changes' log using Entity Framework

During 2018, we worked on an open-source project, and one of the exciting things that we did there was to create an excellent way to have an entity changes' logs. The solution was exciting, but not so good if you wanted to reuse that. So, we decided to create a library to make it easier for anyone that wants to use it!

Download it using NuGet

Install-Package HodStudio.EntityFrameworkDiffLog

Link: https://www.nuget.org/packages/HodStudio.EntityFrameworkDiffLog

How to use

After installing the library via NuGet, you need to make some modifications.

Include the LoggedEntity on your Entities

To know which entities will generate the changelogs, the EntityFrameworkDiffLog will use the LoggedEntity attribute to execute it. If you use the attribute without providing the property name, it uses the default ("Id"). Pay attention that it's case sensitive.

using HodStudio.EntityFrameworkDiffLog.Model;

[LoggedEntity]
public class User
{
    public int Id { get; set; }
    public string UserName { get; set; }
}

In case you have an entity which the Id property is not named "Id," you can use the overload.

using HodStudio.EntityFrameworkDiffLog.Model;

[LoggedEntity("UserId")]
public class User
{
    public int UserId { get; set; }
    public string UserName { get; set; }
}

To avoid problems, especially during renames, we recommend using the nameof to configure the property name.

using HodStudio.EntityFrameworkDiffLog.Model;

[LoggedEntity(nameof(UserId))]
public class User
{
    public int UserId { get; set; }
    public string UserName { get; set; }
}

Initialize the Dictionary of LoggedEntities

To have a better performance, we create a dictionary with the entities that will be logged and keep it. To do that, initialize the dictionary during the start of the app using the following method:

using System.Reflection;
using HodStudio.EntityFrameworkDiffLog.Repository;

LoggingContext.InitializeIdColumnNames(Assembly.GetEntryAssembly());

In case your models are stored in another assembly (or assemblies), pass them to this parameter.

Change your DbContext

To be able to use the full power of EntityFrameworkDiffLog, the easiest way is to inherit your DbContext from LoggingDbContext.

public class ApplicationDbContext : LoggingDbContext

Change the LogEntries table name

In case you have some configuration about the table name or schema name, change the properties LogEntriesTableName and LogEntriesSchemaName.

public SchoolContext()
{
    LogEntriesTableName = "LogEntries";
    LogEntriesSchemaName = "dbo";
}

Special attention to override methods

In case you have some override on your DbContext class, make sure you call the base, to execute the methods from the LoggingDbContext.

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    // your code here

    base.OnModelCreating(modelBuilder);
}

public override int SaveChanges()
{
    // your code here

    return base.SaveChanges();
}

Add-Migration to generate the LogEntry Database and Update the database

Add-Migration AddLogEntries
Update-Database

Configure the user that is executing the operation

In case your application has authenticated users, it makes sense that you would like to know which user made some operation. Based on that, the EntityFrameworkDiffLog is prepared to log this information too. You need to configure the property UserId from the LoggingDbContext. For example, you can do that on the SaveChanges from your DbContext. This just an example. Please, take the user based on the logic from your application.

public override int SaveChanges()
{
    // your code here

    UserId = System.Threading.Thread.CurrentPrincipal.Identity.Name;

    return base.SaveChanges();
}

Configure the type of id used on your project

In most of the cases, the database generates the id. That creates a problem that the id on the logs would always be as zero. So, to avoid this, we introduced the property IdGeneratedByDatabase. In the case of true (default), the log for added entities occurs after the first SaveChanges. Realize, please, that it executes two SaveChanges to the database: one for the entities itself + updated entities' logs + deleted entities' log and another for the added entities' logs. In case you use, for example, GUID for the Id property, most probably you generate this ID inside your application's logic. In that case, you can turn off this functionality. It executes only one SaveChanges in that case.

public SchoolContext()
{
    IdGeneratedByDatabase = false;
}

If you don't want to use UTC for log time

As the library can be used in several places with different timezones, the default configuration is to use Utc. However, if your application is only used in one timezone, you can configure the library to use the time in the current timezone.

public SchoolContext()
{
    UseUtcTime = false;
}

Examples

The source code contains two examples: one for .Net 4.5 and another for .Net Core 2.2. Both of them are the official tutorials projects from Microsoft. For more information about them, please, take a look at the links below:

• .Net 4.5: https://docs.microsoft.com/en-us/aspnet/mvc/overview/getting-started/getting-started-with-ef-using-mvc/creating-an-entity-framework-data-model-for-an-asp-net-mvc-application
• .Net Core 2.2: https://docs.microsoft.com/en-us/aspnet/core/data/ef-mvc/intro?view=aspnetcore-2.2

We decided to make it available to version .Net Core 2.2, the newest version (3.0) is not used so much yet.

Documentation

For more situations and examples, please, take a look at our Documentation on the Wiki.

To see the planned new features, take a look at our RoadMap.