EF Core Linqkit Nested Expressions

LinqKit.Microsoft.EntityFrameworkCore allows you to use the AsExpandable wrapper for writing expressions that can call other expressions. You just need to call the Invoke extension method that will call the inner expression, and calling the Expand extension method will give you the final result.

Let's consider the following simple example.

public static void Example1()
{
    Expression<Func<Book, bool>> criteria1 = b => b.NoOfPages > 1000;
    Expression<Func<Book, bool>> criteria2 = b => b.Title.Contains("Introduction") || criteria1.Invoke(b);

    Console.WriteLine(criteria2.Expand().ToString());
}

Let's run the above code and you will see the following output.

b => (b.Title.Contains("Introduction") OrElse (b.NoOfPages > 1000))

The following example uses the nested expression criteria while retrieving the book's data.

public static void Example2()
{
    Expression<Func<Book, bool>> criteria1 = b => b.NoOfPages > 1000;
    Expression<Func<Book, bool>> criteria2 = b => b.Title.Contains("Introduction") || criteria1.Invoke(b);

    using (var context = new BookStore())
    {
        var books = context.Books.Where(criteria2.Expand()).ToList();

        foreach (var book in books)
        {
            Console.WriteLine("Title: {0} \t Total Pages: {1}", book.Title, book.NoOfPages);
        }
    }
}

You can also call the AsExpandable method on the table and skip the call to the Expand method because AsExpandable automatically calls Expand on expressions as shown below.

public static void Example3()
{
    Expression<Func<Book, bool>> criteria1 = b => b.NoOfPages > 1000;
    Expression<Func<Book, bool>> criteria2 = b => b.Title.Contains("Introduction") || criteria1.Invoke(b);

    using (var context = new BookStore())
    {
        var books = context.Books.AsExpandable().Where(criteria2).ToList();

        foreach (var book in books)
        {
            Console.WriteLine("Title: {0} \t Total Pages: {1}", book.Title, book.NoOfPages);
        }
    }
}

Let's run the above code, and you will see the following output.

Title: Calculus I        Total Pages: 1477
Title: Introduction to Microeconomics    Total Pages: 437
Title: Introduction to Computing         Total Pages: 1171
Title: Introduction to Machine Learning          Total Pages: 530
Title: Calculus II       Total Pages: 1571
Title: Introduction to AI        Total Pages: 530