currently I am working with the NuGet SQLite-Net-Extensions in Xamarin Forms and I have encountered a problem for which I can't find a solution.
The Problem: When calling GetWithChildren(primaryKey, recursive: true), the returned object only contains the first child layer. An example can be seen in the following.
The database is built up like this:
The equivalent code to this model is provided in the following:
User
namespace DatabaseTest
{
[Table("Users")]
public class User
{
[PrimaryKey,AutoIncrement]
public int Id { get; set; }
public string Name { get; set; }
[OneToMany]
public List<Contact> Contacts { get; set; }
}
}
Contact
namespace DatabaseTest
{
[Table("Contacts")]
public class Contact
{
[PrimaryKey,AutoIncrement]
public int Id { get; set; }
public string Name { get; set; }
[OneToMany]
public List<Entry> Entries { get; set; }
[ForeignKey(typeof(User))]
public int UserID { get; set; }
[ManyToOne]
public User User { get; set; }
}
}
Entry
namespace DatabaseTest
{
[Table("Entries")]
public class Entry
{
[PrimaryKey,AutoIncrement]
public int Id { get; set; }
public float Amount { get; set; }
[ForeignKey(typeof(Contact))]
public int ContactId { get; set; }
[ManyToOne]
public Contact Contact { get; set; }
}
}
In my App.cs I am creating the database and use the CreateTable() Method for all three classes. For the sake of this example, in MainPage.xaml.cs there is simply a button, which has a ButtonClicked Method.
In the real Application a process could look like this:
User logs in --> Adds Contact --> At some Point User creates Entry to one of his contacts
To accomplish this procedure in my example, the ButtonClicked Method looks like this:
void ButtonClicked(object sender, EventArgs e)
{
try
{
User user = new User()
{
Name = "Test user"
};
Contact contact = new Contact()
{
Name = "First contact"
};
Entry entry1 = new Entry()
{
Amount = 10F
};
Entry entry2 = new Entry()
{
Amount = 20F
};
App.Database.Insert(user);
if (user.Contacts==null)
{
user.Contacts = new List<Contact>();
}
App.Database.Insert(contact);
user.Contacts.Add(contact);
App.Database.UpdateWithChildren(user);
if (contact.Entries==null)
{
contact.Entries = new List<Entry>();
}
App.Database.Insert(entry1);
App.Database.Insert(entry2);
contact.Entries.Add(entry1);
contact.Entries.Add(entry2);
App.Database.UpdateWithChildren(contact);
App.Database.UpdateWithChildren(user);
var test = App.Database.GetWithChildren<User>(user.Id, recursive: true);
var test2 = App.Database.GetAllWithChildren<Contact>();
var test3 = App.Database.GetAllWithChildren<Entry>();
} catch (Exception ex)
{
Debug.Print(ex.Message);
}
}
I have set a breakpoint to the bracket that closes the try to inspect the result. In the End, my user looks like this:
Which is absolutely perfect.
However, when I try to get this user from my database, the result looks like this:
I don't know how to resolve this error and hope anyone can help me with this problem. Since this post is very long already, I thank everyone who read this far in advance.
After many tries I finally solved my problem on my own.
Solution:
It could not have been any easier. In my User, Contact and Entry Class I provided my OneToMany and ManyToOne attributes with the CascadeOperation attribute. Example:
[OneToMany(CascadeOperations = CascadeOperation.All)]
public List<Entry> Entries { get; set; }
[ManyToOne(CascadeOperations = CascadeOperation.All)]
public User User { get; set; }
Even though I marked my GetWithChildren() Method as recursive: true, only by applying CascadeOperations it will work properly. More information about SQLite-Net-Extensions and CascadeOperations can be found here:
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.