Entity Framework Core Global Filter

Introduction

Entity Framework Core 2.0 introduces global query filters that can be applied to entities when a model is created. It makes it easier to build multi-tenant applications and support soft deleting of entities.

• It allows us to specify a filter in the model level that is automatically applied to all queries that are executed in the context of the specified type.
• It means that entity framework automatically adds the filter in the where clause before executing the LINQ queries.
• Usually, Global query filters are applied in OnModelCreating method of context.

Here is a simple model which contains only one entity i.e., Customer

public class Customer
{
    public int CustomerId { get; set; }
    public string Name { get; set; }
    public bool IsDeleted { get; set; }
}

Global query filters are defined when database context builds the model. So we need to configure the global query filter in OnModelCreating method of context class, using HasQueryFilter method, and we can apply the global filter on the entity type.

public class MyContext : DbContext
{
    public DbSet<Customer> Customers { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer(@"Data Source=(localdb)\ProjectsV13;Initial Catalog=CustomerDB;");
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Customer>().HasQueryFilter(c => !c.IsDeleted);
    }
}

The expression passed in HasQueryFilter method is automatically applied to any LINQ queries for Customer Type. We have four records in the Customers table in the database.

One record is soft deleted already, and the IsDeleted column contains a True value for that record. Now if we retrieve all the all the customers from the database using the LINQ query.

using (var context = new MyContext())
{
    var customers = context.Customers.ToList();
}

We will get only three records, but in the database, we have four records, Because the global filter has filtered records and returns only those records whose IsDeleted column contains False value.

In some cases, we do not need these filters to be applied, we can also disable filter for individual LINQ queries using the IgnoreQueryFilters() method.

using (var context = new MyContext())
{
    var customers = context.Customers
        .IgnoreQueryFilters().ToList();
}

Now the filter won't be applied, and you will get all the records.