EntityFramework.Filters

Filters implementation for Entity Framework, on NuGet as the EntityFramework.Filters package.

Filters allow you to define a parameterized filter at configuration time. At runtime, you turn on the filter and apply parameters, and every query for that entity will include the filter.

Configuration

The FilterInterceptor must be registered with Entity Framework, either through a DbConfiguration class:

public class ExampleConfiguration : DbConfiguration
{
    public ExampleConfiguration()
    {
        AddInterceptor(new FilterInterceptor());
    }
}

Or through the OnModelCreating method:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    DbInterception.Add(new FilterInterceptor());
}

Examples

Filters are first defined, then configured. You define the filter against a single entity:

modelBuilder.Entity<Listing>()
    .Filter("ActiveListings", c => c.Condition<ListingStatus>(
        listing => listing.Status == ListingStatus.Active));

Or against a set of entities that match a type (interface or base class):

modelBuilder.Conventions.Add(
    FilterConvention.Create<IAgencyEntity, int>("Agency", (e, agencyId) => e.AgencyId == agencyId);

Filters are then enabled and parameter values filled in on a DbContext basis:

dbContext.EnableFilter("ActiveListings");
dbContext.EnableFilter("Agency")
    .SetParameter("agencyId", _userContext.CurrentUser.AgencyId);

Filters are disabled by default, and you can disable them selectively after enabling:

dbContext.DisableFilter("ActiveListings");

The filter names must be unique, and filter parameter names are matched by the parameter name you supply to the filter definition's expression.

Common Usages

Filters are used to define a predicate that will be applied to every entity in a DbContext, without a developer needing to remember to include it for every query. Common applications include:

• Security
• Multi-tenancy
• Logical data partitioning
• Soft deletes
• Active/inactive records

There are some limitations, however:

• No access to context for complex joins
• Collection properties not available