Entity Framework Core - QueryFilterBuilder

This library solves a certain problem shown in the image below. This library adds an extension method to the EntityTypeBuilder class that allows the use of HasQueryFilter() by passing to it an instance of the QueryFilterBuilder class also provided by this library. The class allows you to combine multiple rules/filters and then by calling the Build() method, combining them into one filter (LINQ expression predicate) that can be used in the HasQueryFilter() method.

The method of adding a filter has a bool parameter that indicates whether the filter should be used or not. Thanks to this, any service injected into DbContext can control which filters should be applied in a given scope.

The EFCore.QueryFilterBuilder tags are related to the underlying Microsoft.EntityFrameworkCore dependency version.

Example

An example of using QueryFilterBuilder in the override OnModelCreating() method in the DbContext class.

protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
	    // Fluent API (First way, specified multiple filters)
	    modelBuilder.Entity<Blog>()
			.HasQueryFilters()
				.AddFilter(b => b.Name == "Hello World")
        		.AddFilter(b => b.Posts == 20, _injectedService.ShouldApplyFilter())
            	.Build()
			
			// We can later chain other EntityTypeBuilder methods...


		// Fluent API (Second way, un-specified multiple filters)
		modelBuilder.Entity<Blog>()
			.HasQueryFilter(b => b.Name == "Hello World")
				.AddFilter(b => b.Posts == 20, _injectedService.ShouldApplyFilter())
				.Build()

			// We can later chain other EntityTypeBuilder methods...


		// Fluent API (Third way, cached QueryFilterBuilder)
		var queryFilterBuilder = QueryFilterBuilder<Blog>
			.Create()
			.AddFilter(b => b.Name == "Hello World")
        	.AddFilter(b => b.Posts == 20, _injectedService.ShouldApplyFilter())

		
		modelBuilder.Entity<Blog>().HasQueryFilter(queryFilterBuilder)

		// We can later chain other EntityTypeBuilder methods...
    }