The Fluent API HasQueryFilter Method

The Entity Framework Core Fluent API HasQueryFilter method is used to apply a global query filter to a specific entity, so that the filter is included in all query statements generated for the entity by EF Core. The most common use cases for this feature include properties that indicate that an entity instance is deleted, or not otherwise active, and a tenant identifier in an application that houses data for multiple tenants.

The following example illustrates the second scenario. The code presents two entities; a Magazine and a Story. They might represent part of a model for a web application that caters for multiple magazines in the same database. In this example, the Magazine is the tenant.

public class Magazine
{
    public int MagazineId { get; set; }
    public string Title { get; set; }
}

public class Story
{
    public int StoryId { get; set; }
    public string Headline { get; set; }
    public string Content { get; set; }
    public int MagazineId { get; set; }
    public Magazine Magazine { get; set; }
}

The HasQueryFilter method is applied to the Magazine entity in OnModelCreating:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Magazine>().HasQueryFilter(m => EF.Property<int>(m, "MagazineId") == 1);
}

In this case the value that is used to filter queries by is hard coded. Normally, it will be based on the result of whatever algorithm is used to determine the current MagazineId (a global variable, a custom header value, the URL etc). Any query that includes the Magazine entity will have the filter applied e.g.

var stories = db.Stories.Include(s => s.Magazine);

If you do not want to have the filter applied, use the IgnoreQueryFilters method:

var stories = db.Stories.Include(s => s.Magazine).IgnoreQueryFilters();

The next example shows how to use the query filter to automatically exclude products that have been flagged a discontinued from all queries. The model definition:

public class Product
{
    public int ProductId { get; set; }
    public string ProductName { get; set; }
    public bool Discontinued { get; set; }
}

Again, the query filter is applied in the OnModelCreating method, and will result in queries that reference the Product entity only returning hose that have not been discontinued:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Product>().HasQueryFilter(p => EF.Property<bool>(p, "Discontinued") == false);
}

The query is defined:

var products = context.Products.ToList();

The resulting SQL that is generated automatically includes the filter:

info: Microsoft.EntityFrameworkCore.Database.Command[20101]
      Executed DbCommand (1ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
      SELECT "p"."ProductId", "p"."Discontinued", "p"."ProductName"
      FROM "Products" AS "p"
      WHERE "p"."Discontinued" = 0
Total Products: 8

Data Annotations

There is no Data Annotations equivalent for the HasQueryFilter method.

Last updated: 14/08/2019 09:26:27

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