Entity Framework Filters

Definition

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.

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

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());
}

Define Filters

Single Entity

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));

Set of Entities

Filters are also defined 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);

Enable Filters

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

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

Disable Filters

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.

Requirements

Entity Framework Version

• Entity Framework 6.

Limitations

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

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