EF Core Include Discover How to Retrieve Related Objects in LINQ
Include
The Include method specifies the related objects to include in the query results. It can be used to retrieve some information from the database and also want to include related entities. Now let's say we have a simple model which contains three entities.
public class Customer { public int CustomerId { get; set; } public string FirstName { get; set; } public string LastName { get; set; } public string Address { get; set; } public virtual List<Invoice> Invoices { get; set; } } public class Invoice { public int InvoiceId { get; set; } public DateTime Date { get; set; } public int CustomerId { get; set; } [ForeignKey("CustomerId")] public Customer Customer { get; set; } public List<InvoiceItem> Items { get; set; } } public class InvoiceItem { public int InvoiceItemId { get; set; } public int InvoiceId { get; set; } public string Code { get; set; } [ForeignKey("InvoiceId")] public virtual Invoice Invoice { get; set; } }
Now to retrieve all customers and their related invoices we have to use the Include Method.
using (var context = new MyContext()) { var customers = context.Customers .Include(c => c.Invoices) .ToList(); }
ThenInclude
The Include method works quite well for Lists on objects, but what if there is a need for multiple levels of depth. For example, Customer contains a list of invoices and each invoice then contains a list of items.
EF Core has a new extension method ThenInclude(). You can drill down thru relationships to include multiple levels of related data using the ThenInclude method.
using (var context = new MyContext()) { var customers = context.Customers .Include(i => i.Invoices) .ThenInclude(it => it.Items) .ToList(); }
Author: ZZZ Projects