How to store unique class instances in SQLite? - sqlite

Question

I'm trying to store some information as a class instance in a SQLite table. The instances need to be unique in their DateTime property. I'm completely new to database programming, and I don't really understand how use SQLite in Xamarin. As new instances are created they need to update the existing instances in the table if they match in their DateTime property.
SQLiteAsyncConnection connection = new SQLiteAsyncConnection(App.FilePath);
await connection.CreateTableAsync<ModulInformationData>();
ModulInformationData data = new ModulInformationData();
data.InitModulInformation(modul);
int rows = 0;
try
{
rows = await connection.UpdateAsync(data);
}catch(Exception e)
{
Console.WriteLine("SQL Update failed " + e.Message);
}
Console.WriteLine("rows updated: " + rows);
if (rows == 0)
{
Console.WriteLine("before insert");
try
{
int key1 = await connection.InsertAsync(data);
Console.WriteLine("after insert: " + key1);
}catch (Exception e)
{
Console.WriteLine("SQL insert failed " + e.Message);
}
}
The ModulInformationData class
public class ModulInformationData
{
[PrimaryKey,AutoIncrement]
public int Id { get; set; }
[Unique]
public DateTime tidspunkt { get; set; }
other properties...
At the moment, I'm catching an error when inserting, but the message only says 'Constraint'. What can I do to make this work?

Answer 1

Do you want to achieve the result like this GIF。
First of all, you can create a class for the database CRUD.
public class NoteDatabase
{
readonly SQLiteAsyncConnection _database;
public NoteDatabase(string dbPath)
{
_database = new SQLiteAsyncConnection(dbPath);
_database.CreateTableAsync<Note>().Wait();
}
public Task<List<Note>> GetNotesAsync()
{
return _database.Table<Note>().ToListAsync();
}
public Task<Note> GetNoteAsync(int id)
{
return _database.Table<Note>()
.Where(i => i.ID == id)
.FirstOrDefaultAsync();
}
public Task<int> SaveNoteAsync(Note note)
{
if (note.ID != 0)
{
return _database.UpdateAsync(note);
}
else
{
return _database.InsertAsync(note);
}
}
public Task<int> DeleteNoteAsync(Note note)
{
return _database.DeleteAsync(note);
}
}
Then there is model class.
public class Note
{
[PrimaryKey, AutoIncrement]
public int ID { get; set; }
public string Text { get; set; }
[Unique]
public DateTime Date { get; set; }
public string Gender { get; set; }
}
If we want to add or update the data to the database, firstly, we should update the data to the instance, then we could just save this instance to the database like following save click event.
async void OnSaveButtonClicked(object sender, EventArgs e)
{
var note = (Note)BindingContext;
note.Date = DateTime.UtcNow;
note.Gender = (string)myPicker.SelectedItem;
await App.Database.SaveNoteAsync(note);
await Navigation.PopAsync();
}
Here is my demo. you can download it and refer to it.
https://github.com/851265601/databaseDemo