karenpayneoregon / efcore-shadow-properties

Example for Entity Framework Core shadow properties

EF Core Global Query Filters

Learn how to

• Create global query filters which are LINQ query predicates applied to Entity Types, in this article, your models. A typical example, using soft delete, only show those records which are active which will be gone over in code.
• Override global query filters see also
• Override a DbContext SaveChangesAsync and SaveChanges to handle soft deletes.
• Create an Excel file using SpreadSheetLight with NuGet package.
  • I included SpreadSheetLight chm file outside the solution under folder SpreadSheetLightHelp as some may find if hard to get from SpreadSheetLight site.
• Using FastMember.NetCore to create a DataTable from a generic List for use with creating an Excel file.

Limitations

Filters can only be defined for the root Entity Type of an inheritance hierarchy.

Core Projects

• ShadowProperties, class project for data operations
• HasQueryFilterRazorApp, Razor Pages project which
  • Presents data
  • Provides an interface to soft delete records
  • Provides an interface to un-delete soft deletes.

Windows forms projects

There are two projects, Backend and DemoShadowProperties. These are from the following Microsoft TechNet article Entity Framework Core shadow properties (C#) which were done with .NET Framework 4.7 and have been updated to 4.8.

The Core projects were based off these projects which shows when writing decent code a we have a good start to port to ASP.NET Core and Razor Pages.

Database

Schema for the table used to demonstrate using global query filters.

Columns

• isDeleted soft delete flag
• CreatedBy user which added the record
• CreatedAt when the record was added date time
• LastUser user to last modify a record
• LastUpdated last updated date time

SQL to examine data in SSMS

SELECT ContactId,
       FirstName,
       LastName,
       LastUser,
       CreatedBy,
	   FORMAT(CreatedAt, 'MM/dd/yyyy') AS CreatedAt,
	   FORMAT(LastUpdated, 'MM/dd/yyyy') AS LastUpdated,
       IIF(isDeleted = 'TRUE' , 'Y','N') AS Deleted
FROM dbo.Contact1;

Setup a global query filter

In the DbContext OnModelCreating method, after the entities have been configured add.

modelBuilder.Entity<Contact>()
    .HasQueryFilter(contact =>
        EF.Property<bool>(contact, "isDeleted") 
        == false);

That's it. In the Index page to get contacts.

Read filtered records

public async Task OnGetAsync()
{

    if (_context.Contacts != null)
    {
        Contacts = await _context.Contacts.ToListAsync();
    }
}

Generated SQL, note the WHERE clause.

SELECT [c].[ContactId], [c].[CreatedAt], [c].[CreatedBy], [c].[FirstName], [c].[LastName], [c].[LastUpdated], [c].[LastUser], [c].[isDeleted]
FROM [Contact1] AS [c]
WHERE [c].[isDeleted] = CAST(0 AS bit)

🛑 did you notice in the database the table name is Contact1 but in the above code we are using Contact model. This is done via Table name annotations.

[Table("Contact1")]
public partial class Contact : INotifyPropertyChanged

Ignore filters

IgnoreQueryFilters extension Specifies that the current Entity Framework LINQ query should not have any model-level entity query filters applied.

public async Task OnGetAsync()
{
    if (_context.Contacts != null)
    {
        Contacts = await _context
            .Contacts
            .IgnoreQueryFilters() // IMPORTANT
            .ToListAsync();
    }
}

Handling soft deletes

Working in DeleteContactPage.

• An id is passed from the index page
• Find and validate the contact exists still
• Begin tracking the contact marked as deleted.

public async Task<IActionResult> OnPostAsync(int? id)
{
    if (id == null || _context.Contacts == null)
    {
        return NotFound();
    }
    var contact = await _context.Contacts.FindAsync(id);

    if (contact != null)
    {
        Contact = contact;
        _context.Contacts.Remove(Contact);
        await _context.SaveChangesAsync();
    }

    return RedirectToPage("./Index");
}

Back in the DbContext we override SaveChangesAsync.

public override Task<int> SaveChangesAsync(CancellationToken cancellationToken = new ())
{
    HandleChanges();
    return base.SaveChangesAsync(cancellationToken);
}

HandleChanges method

• Traverse entities, if the state is EntityState.Deleted, set its state to Modfied followed by setting isDeleted to true.

private void HandleChanges()
{
    foreach (var entry in ChangeTracker.Entries())
    {
        // take care of date time created and updated
        if (entry.State is EntityState.Added or EntityState.Modified)
        {
            entry.Property("LastUpdated").CurrentValue = DateTime.Now;
            entry.Property("LastUser").CurrentValue = Environment.UserName;

            if (entry.Entity is Contact && entry.State == EntityState.Added)
            {
                entry.Property("CreatedAt").CurrentValue = DateTime.Now;
                entry.Property("CreatedBy").CurrentValue = Environment.UserName;
            }
        }
        else if (entry.State == EntityState.Deleted)
        {
            // Change state to modified and set delete flag
            entry.State = EntityState.Modified;
            entry.Property("isDeleted").CurrentValue = true;
        }
    }
}

WCAG Accessibility

All pages conform to WCAG AA standard.

Note that the checkbox on the admin page needed aria-label attribute for screen readers to properly identify the checkbox purpose.

Admin page

This page allows the user to perform deletions and un delete operations which are respected by the global in place.

Soure code

Clone the following GitHub repository

Next step

Is to work with an Interceptor and interface.

For this see How to Implement a Soft Delete Strategy with Entity Framework Core. Going this way is a personal choice and in this article moving in this direction will be easy as this code and mine are compatible.