Say goodbye to the hassle of having to manually set a default filter for every query
EF Core provides a useful feature called Global Query Filters. It enables you to apply a filter to all queries sent to the database. Two examples of how this feature can be practically used are implementing soft delete and creating a multitenant database.
Building your own query filter
I will assume that you have already established the Database Context class for EF Core.
To add custom query filters, simply modify the OnModelCreating method in the DatabaseContext. Remember, setting query filters only affects specific tables within the database. To filter each table globally, we need to set a query filter on that particular entity.
For instance, the following piece of code creates a global query filter to ignore soft-deleted users:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
// Add a query filter to ignore all soft-deleted users
modelBuilder.Entity<User>().HasQueryFilter(u => !u.IsDeleted);
}
Using extension methods
One thing I enjoy doing is developing an extension method that contains the soft delete logic and then implementing it as a query filter.
public static class ModelBuildExtensions
{
public static void AddIsDeletedQueryFilter<T>(this ModelBuilder modelBuilder) where T : class, IBaseEntity
{
modelBuilder.Entity<T>().HasQueryFilter(u => !u.IsDeleted);
}
}
With the use of this extension method, it is now possible to add soft delete global query filters in the following way:
// Add soft-delete global query filter for all of these entities
modelBuilder.AddIsDeletedQueryFilter<User>();
modelBuilder.AddIsDeletedQueryFilter<Image>();
modelBuilder.AddIsDeletedQueryFilter<Comment>();
modelBuilder.AddIsDeletedQueryFilter<Article>();
Ignoring global query filters
Having global query filters is great, but what if you need to view soft-deleted users specifically?
Fortunately, we can bypass global query filters by using the IgnoreQueryFilters() method through chaining.
var softDeletedUsers = _databaseContext.Users
.IgnoreQueryFilters() // this line does the magic
.Where(user => user.IsDeleted)
.ToList();
Using multiple query filters
Unfortunately, EF Core does not allow you to define multiple query filters on the same entity.
// This won't work, as an entity can only have one query filter in EF Core
modelBuilder.Entity<User>()
.HasQueryFilter(u => !u.Age < 18)
.HasQueryFilter(u => !u.IsDeleted);
At the time of writing this, this is currently an open issue on the EF Core Github page: https://github.com/dotnet/efcore/issues/10275.
But, if your query filter is straightforward, you can combine them into one query filter.
// This will work, as it's only one query filter
modelBuilder.Entity<User>()
.HasQueryFilter(u => !u.Age < 18 || !u.IsDeleted);