EF7 Read Master Detail Records - entity-framework

Question

I'm trying to get my head around EF7 by writing a simple master-detail relationship to a sqlite database. Saving works fine, reading however gives me headaches:
Here are my Entities:
public class Message
{
public int MessageId { get; set; }
public string Name { get; set; }
public List<MessagePart> MessageParts { get; set; }
}
public class MessagePart
{
public int MessagePartId { get; set; }
public string Text { get; set; }
public int MessageId { get; set; }
public Message Message { get; set; }
}
createMessage() does what it is supposed to:
static void createMessages()
{
using (var db = new TestContext())
{
var m1 = new Message
{
Name = "train_arrives_in_x_minutes",
MessageParts = new List<MessagePart>()
{
new MessagePart {
Text = "Train arrives in 5 minutes"
},
new MessagePart {
Text = "Zug faehrt in 5 Minuten ein",
}
}
};
var m2 = new Message
{
Name = "train_out_of_service",
MessageParts = new List<MessagePart>()
{
new MessagePart {
Text = "train is out of service"
},
new MessagePart {
Text = "Kein Service auf dieser Strecke",
}
}
};
db.Messages.Add(m1);
db.Messages.Add(m2);
var count = db.SaveChanges();
Console.WriteLine("{0} records saved to database", count);
}
}
Reading from an existing database reads the master record fine, but the detail recordset pointer stays null.
static void readMessages()
{
using (var db = new TestContext())
{
foreach (Message m in db.Messages)
{
Console.WriteLine(m.Name);
// exception here: m.MessageParts is always null
foreach(MessagePart mp in m.MessageParts)
{
Console.WriteLine("mp.Text={0}", mp.Text);
}
}
}
}
Is there anything I can do to force those messagesparts to load? I've worked with other (Python) ORMs before and never had this problem before. Is this a problem with Lazy Loading? I tried to fetch those childrecords using a LINQ statement, that didn't help either. Everything looks good in the database though.

Answer 1

If you want to enable LazyLoading you need to enable LazyLoading (should be enabled by default) and make your property virtual:
public TestContext()
: base(Name = "ConntextionName")
{
this.Configuration.ProxyCreationEnabled = true;
this.Configuration.LazyLoadingEnabled = true;
}
And your models shuodl look like:
public class Message
{
public int MessageId { get; set; }
public string Name { get; set; }
public virtual ICollection<MessagePart> MessageParts { get; set; }
}
public class MessagePart
{
public int MessagePartId { get; set; }
public string Text { get; set; }
public int MessageId { get; set; }
public virtual Message Message { get; set; }
}
If you do not want to use LazyLoading, you can load related entities using eager loading:
using System.Data.Entity;
using (var db = new TestContext())
{
int messageId = ....;
Message message = db.Messages
.Where(m => m.MessageId == messageId)
.Include(m => m.MessageParts) // Eagerly load message parts
.FirstOrDefault();
// Your message and all related message parts are now loaded and ready.
}
For more information, please have a look at this site.