In addition to expanding results with associated data it's possible to navigate to linked entries directly, without fetching it's relationship principle. The relationship must be defined in OData service schema.

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IEnumerable<dynamic> products = _db.Products
    .FindAll(_db.Products.Category.CategoryName == "Beverages");
Assert.NotEmpty(products);

Request URI: GET Products?$filter=Category%2fCategoryName+eq+%27Beverages%27

---

IEnumerable<dynamic> employees = _db.Employees
    .FindAll(_db.Employees.Superior.FirstName == "Andrew" && _db.Employees.Superior.LastName == "Fuller");
Assert.NotEmpty(employees);

Request URI: GET Employees?$filter=Superior/FirstName+eq+%27Nancy%27 and Superior/LastName+eq+%27Davolio%27

---

IEnumerable<dynamic> orders = _db.Orders
    .FindAll(_db.Orders.Employee.FirstName == "Andrew" && _db.Orders.Employee.LastName == "Fuller");
Assert.NotEmpty(orders);

Request URI: GET Orders?$filter=Employee/FirstName+eq+%27Andrew%27 and Employee/LastName+eq+%27Fuller%27

---

IEnumerable<dynamic> orders = _db.Customers
    .Orders
    .FindAll(_db.Customers.CustomerID == "ALFKI");
Assert.NotEmpty(orders);

Request URI: GET Customers('ALFKI')/Orders

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IEnumerable<dynamic> orderDetails = _db.Orders
    .OrderDetails
    .FindAll(_db.Orders.OrderID == 10952);
Assert.NotEmpty(orderDetails);

Request URI: GET Orders(10952)/OrderDetails

---

IEnumerable<dynamic> subordinates = _db.Employees
    .Subordinates
    .FindAll(_db.Employees.EmployeeID == 2);
Assert.NotEmpty(subordinates);

Request URI: GET Employees(1)/Subordinates

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var superior = _db.Employees
    .Superior
    .Get(1);
Assert.NotNull(superior);

Request URI: GET Employees(1)/Superior

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var superior = _db.Employees
    .Superior
    .Find(_db.Employees.EmployeeID == 1);
Assert.Equal(2, superior.EmployeeID);

Request URI: GET Employees(1)/Superior

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IEnumerable<dynamic> superiors = _db.Employees
    .Superior
    .FindAll(_db.Employees.EmployeeID == 1);
Assert.NotEmpty(superiors);

Request URI: GET Employees(1)/Superior

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See also:
Expanding results with linked entries
Retrieving data