Global Query Filters

Global query filters are LINQ query predicates applied to Entity Types in the metadata model (usually in OnModelCreating). A query predicate is a boolean expression typically passed to the LINQ Where query operator. EF Core applies such filters automatically to any LINQ queries involving those Entity Types. EF Core also applies them to Entity Types, referenced indirectly through use of Include or navigation property. Some common applications of this feature are:

• Soft delete - An Entity Type defines an IsDeleted property.
• Multi-tenancy - An Entity Type defines a TenantId property.

Example

The following example shows how to use Global Query Filters to implement multi-tenancy and soft-delete query behaviors in a simple blogging model.

Tip

You can view this article's sample on GitHub.

Note

Multi-tenancy is used here as a simple example. There is also an article with comprehensive guidance for multi-tenancy in EF Core applications.

First, define the entities:

public class Blog
{
#pragma warning disable IDE0051, CS0169 // Remove unused private members
    private string _tenantId;
#pragma warning restore IDE0051, CS0169 // Remove unused private members

    public int BlogId { get; set; }
    public string Name { get; set; }
    public string Url { get; set; }

    public List<Post> Posts { get; set; }
}

public class Post
{
    public int PostId { get; set; }
    public string Title { get; set; }
    public string Content { get; set; }
    public bool IsDeleted { get; set; }

    public Blog Blog { get; set; }
}

Note the declaration of a _tenantId field on the Blog entity. This field will be used to associate each Blog instance with a specific tenant. Also defined is an IsDeleted property on the Post entity type. This property is used to keep track of whether a post instance has been "soft-deleted". That is, the instance is marked as deleted without physically removing the underlying data.

Next, configure the query filters in OnModelCreating using the HasQueryFilter API.

modelBuilder.Entity<Blog>().HasQueryFilter(b => EF.Property<string>(b, "_tenantId") == _tenantId);
modelBuilder.Entity<Post>().HasQueryFilter(p => !p.IsDeleted);

The predicate expressions passed to the HasQueryFilter calls will now automatically be applied to any LINQ queries for those types.

Tip

Note the use of a DbContext instance level field: _tenantId used to set the current tenant. Model-level filters will use the value from the correct context instance (that is, the instance that is executing the query).

Note

It is currently not possible to define multiple query filters on the same entity - only the last one will be applied. However, you can define a single filter with multiple conditions using the logical AND operator (&& in C#).

Use of navigations

You can also use navigations in defining global query filters. Using navigations in query filter will cause query filters to be applied recursively. When EF Core expands navigations used in query filters, it will also apply query filters defined on referenced entities.

To illustrate this configure query filters in OnModelCreating in the following way:

modelBuilder.Entity<Blog>().HasMany(b => b.Posts).WithOne(p => p.Blog);
modelBuilder.Entity<Blog>().HasQueryFilter(b => b.Posts.Count > 0);
modelBuilder.Entity<Post>().HasQueryFilter(p => p.Title.Contains("fish"));

Next, query for all Blog entities:

var filteredBlogs = db.Blogs.ToList();

This query produces the following SQL, which applies query filters defined for both Blog and Post entities:

SELECT [b].[BlogId], [b].[Name], [b].[Url]
FROM [Blogs] AS [b]
WHERE (
    SELECT COUNT(*)
    FROM [Posts] AS [p]
    WHERE ([p].[Title] LIKE N'%fish%') AND ([b].[BlogId] = [p].[BlogId])) > 0

Note

Currently EF Core does not detect cycles in global query filter definitions, so you should be careful when defining them. If specified incorrectly, cycles could lead to infinite loops during query translation.

Accessing entity with query filter using required navigation

Caution

Using required navigation to access entity which has global query filter defined may lead to unexpected results.

Required navigation expects the related entity to always be present. If necessary related entity is filtered out by the query filter, the parent entity wouldn't be in result either. So you may get fewer elements than expected in result.

To illustrate the problem, we can use the Blog and Post entities specified above and the following OnModelCreating method:

modelBuilder.Entity<Blog>().HasMany(b => b.Posts).WithOne(p => p.Blog).IsRequired();
modelBuilder.Entity<Blog>().HasQueryFilter(b => b.Url.Contains("fish"));

The model can be seeded with the following data:

db.Blogs.Add(
    new Blog
    {
        Url = "http://sample.com/blogs/fish",
        Posts = new List<Post>
        {
            new Post { Title = "Fish care 101" },
            new Post { Title = "Caring for tropical fish" },
            new Post { Title = "Types of ornamental fish" }
        }
    });

db.Blogs.Add(
    new Blog
    {
        Url = "http://sample.com/blogs/cats",
        Posts = new List<Post>
        {
            new Post { Title = "Cat care 101" },
            new Post { Title = "Caring for tropical cats" },
            new Post { Title = "Types of ornamental cats" }
        }
    });

The problem can be observed when executing two queries:

var allPosts = db.Posts.ToList();
var allPostsWithBlogsIncluded = db.Posts.Include(p => p.Blog).ToList();

With above setup, the first query returns all 6 Posts, however the second query only returns 3. This mismatch happens because Include method in the second query loads the related Blog entities. Since the navigation between Blog and Post is required, EF Core uses INNER JOIN when constructing the query:

SELECT [p].[PostId], [p].[BlogId], [p].[Content], [p].[IsDeleted], [p].[Title], [t].[BlogId], [t].[Name], [t].[Url]
FROM [Posts] AS [p]
INNER JOIN (
    SELECT [b].[BlogId], [b].[Name], [b].[Url]
    FROM [Blogs] AS [b]
    WHERE [b].[Url] LIKE N'%fish%'
) AS [t] ON [p].[BlogId] = [t].[BlogId]

Use of the INNER JOIN filters out all Posts whose related Blogs have been removed by a global query filter.

It can be addressed by using optional navigation instead of required. This way the first query stays the same as before, however the second query will now generate LEFT JOIN and return 6 results.

modelBuilder.Entity<Blog>().HasMany(b => b.Posts).WithOne(p => p.Blog).IsRequired(false);
modelBuilder.Entity<Blog>().HasQueryFilter(b => b.Url.Contains("fish"));

Alternative approach is to specify consistent filters on both Blog and Post entities. This way matching filters are applied to both Blog and Post. Posts that could end up in unexpected state are removed and both queries return 3 results.

modelBuilder.Entity<Blog>().HasMany(b => b.Posts).WithOne(p => p.Blog).IsRequired();
modelBuilder.Entity<Blog>().HasQueryFilter(b => b.Url.Contains("fish"));
modelBuilder.Entity<Post>().HasQueryFilter(p => p.Blog.Url.Contains("fish"));

Disabling Filters

Filters may be disabled for individual LINQ queries by using the IgnoreQueryFilters operator.

blogs = db.Blogs
    .Include(b => b.Posts)
    .IgnoreQueryFilters()
    .ToList();

Limitations

Global query filters have the following limitations:

• Filters can only be defined for the root Entity Type of an inheritance hierarchy.