尝试使用 C# 实体框架检索嵌入式/相关类

Question

Suppose I have a data structure like this - where a Person object may have many addresses, and an address may have manny address lines.

public class Person
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public List<Address> Addresses { get; set; }
}


public class Address
{
    public int Id { get; set; }
    public List<AddressLine> AddressLines { get; set; } 
    public string PostCode { get; set; }
}

public class AddressLine
{
    public int Id { get; set; }
    public string AddressLine
}

I have then used Entity framework to allow this data structure to be stored into my database thus:

public class DatabaseContext : DbContext
{
    public DatabaseContext() : base("name=DatabaseConnection") { }
    public DatabaseContext(string connectionString) : base(connectionString) { }
    public DbSet<Person> People { get; set; }
}

Finally, I have a class which interacts with this database:

public class ProcessPeople
{
    private DatabaseContext localDatabase;

    ProcessPeople(DatabaseContext db)
    {
        localDatabase = db;
    }

    public DoProcessingOfPerson(int idOfPerson)
    {
         Person person =
                localDatabase.People.Where(p => p.Id.Equals(idOfPerson)).FirstOrDefault();

         Console.WriteLine("First  : " + person.FirstName);
         Console.WriteLine("Last   : " + person.LastName);

         // Print address
         if(person.Addresses != null && person.Addresses.Count > 0)
         {
             if(person.Addresses[0].AddressLines != null && person.Addresses[0].AddressLines.Count > 0)
             {
                 Console.WriteLine("Address: " + person.Addresses[0].AddressLines[0].AddressLine);
             }
         }
         else
         {
             Console.WriteLine("No address available");
         }
    }
}

The problem is that after the person is retrieved using the code:

Person person =
      localDatabase.People.Where(p => p.Id.Equals(idOfPerson)).FirstOrDefault();

The Addresses array is always null - even though there is definitely related Address and AddressLine data in there.

My question:

How does one do a retrieval from the Entity framework database such that all the data in the embedded classes inside the Person class are also retrieved?

I am wanting to pull back a person, and then be able to navigate through the Addresses and AddressLines arrays - but these classes are not being retrieved from the database [even though they exist in the actual database that has been generated by entity framework]

Note that for brevity, i have not included the data input code - I am just looking for what i need to do to this line:

Person person =
    localDatabase.People.Where(p => p.Id.Equals(idOfPerson)).FirstOrDefault();

In order to get all objects and sub-objects populated in the variable "person", assuming the related data exists.

thanks heaps for any assistance

David.

Answer 1

You should use Include as following:

Person person = localDatabase.People
                                .Include(p=> p.Addresses)
                                    .ThenInclude(add => add.AddressLine)
                                .Where(p => p.Id.Equals(idOfPerson)).FirstOrDefault();

For more detail: Loading Related Entities