Xamarin Forms SQLLite add OneToOne and OneToMany subobjects to db - sqlite

Question

Im trying to create a persistent sqllite db (creation tables once you install the app, deletion of db when you uninstall app)
I have a issue that I cant save my sub objects for example
public class ObjectInstanceResponseModel : GenericResponseModel
{
public ObservableCollection<ObjectInstanceData> ObjectInstances { get; set; }
}
public class ObjectInstanceData : GenericResponseModel
{
[PrimaryKey, AutoIncrement]
public int Id { get; set; }
[JsonProperty("idObjectinstance")]
public int IdObjectInstance { get; set; }
[JsonProperty("objectclass_idObjectclass")]
public int ObjectClassIdObjectClass { get; set; }
[JsonProperty("objectclassname")]
public string ObjectClassName { get; set; }
[JsonProperty("visibilitylevel")]
public int VisibilityLevel { get; set; }
[JsonProperty("showname")]
public bool ShowName { get; set; }
[JsonProperty("showicon")]
public bool ShowIcon { get; set; }
[JsonProperty("creationtime")]
public DateTimeOffset CreationTime { get; set; }
[JsonProperty("users_idUsers")]
public int UsersIdUsers { get; set; }
[JsonProperty("isfavorite")]
public bool? IsFavorite { get; set; }
[OneToMany("ObjectInstanceDataStrings")]
[JsonProperty("strings")]
public List<String> Strings { get; set; }
}
public class String
{
[PrimaryKey, AutoIncrement]
[JsonProperty("idObjectparameterstring")]
public int? IdObjectParameterString { get; set; }
[ForeignKey(typeof(ObjectInstanceData))]
public int ObjectInstanceDataStrings { get; set; }
[JsonProperty("stringvalue")]
public string StringValue { get; set; }
[JsonProperty("objectparameterset_idObjectparameterset")]
public int? ObjectParameterSetIdObjectParameterSet { get; set; }
[JsonProperty("showinballon")]
public bool? ShowInBallon { get; set; }
[JsonProperty("idClassparameter")]
public int IdClassParameter { get; set; }
[JsonProperty("classparametername")]
public string ClassParameterName { get; set; }
}
So, my class String is always empty, although there are some rows in the table that I created Strings..
Am I need a lazy loading for this?
I implemented sqllite through depedency service in my app.cs like this:
public partial class App : Application
{
public static SQLiteConnection DatabaseConnection { get; set; }
public App()
{
InitializeComponent();
DatabaseConnection = DependencyService.Get<IConnection>().GetConnection();
CreateTables();
}
private void CreateTables()
{
DatabaseConnection.CreateTable<ObjectInstanceData>();
DatabaseConnection.CreateTable<Models.Objects.String>();
}
protected override void OnStart()
{
}
protected override void OnSleep()
{
}
protected override void OnResume()
{
}
}
So, basically the logic should be when no internet, work with sql lite (keep local changes), and when internet come back upload that changes that kept in db, and erase data from tables.
You noticed that Im using response model for api.
So, Im calling from my FavoriteObjectViewModel this:
var response = await ApiServiceProvider.GetObjectInstances(null, true);
and in the ApiServiceProvider:
public static async Task<ObjectInstanceResponseModel> GetObjectInstances(string queryString = null, bool? onlyFavorites = null)
{
HttpResponseMessage response;
response = await apiClient.GetAsync(objectInstancesEndpoint);
var resultContent = await response.Content.ReadAsStringAsync();
var result = JsonConvert.DeserializeObject<ObservableCollection<ObjectInstanceData>>(resultContent);
objectInstanceResponse.ObjectInstances = result;
//after each api call I need to update db
//delete previous data, and add fresh data from api
App.DatabaseConnection.DeleteAll<ObjectInstanceData>();
foreach (var item in result)
{
App.DatabaseConnection.Insert(item);
if (item.Strings != null && item.Strings.Count > 0)
App.DatabaseConnection.InsertAll(item.Strings);
}
//I only get the data for ObjectInstanceData, Strings model is empty!
var objectsResponseDb = App.DatabaseConnection.GetAllWithChildren<ObjectInstanceData>();
objectInstanceResponse.Succeeded = true;
return objectInstanceResponse;
}
So, my questions are:
If I create tables each time in App.cs is that mean, that I not store data, when user quit application, and re-enter again?
Why is the model Strings empty? When I invoke var strings = App.DatabaseConnection.GetAllWithChildren<Models.Objects.String>(); I can see that there is data?
What is the best approach for doing offline "logging"? maybe there is a some better nuget for sqllite?

Answer 1

I don't know much about persistent databases but one thing I can tell you for sure:you're approach is wrong.
You should create a separate class for the database's logic like creating tables and instantiating the connection along with other methods for manipulating data.
In the App class you can create a static resource of the database class which you can call it and make use of the methods in it.
I'm not very good with explaining but here it is a very basic example of how it should look:https://learn.microsoft.com/en-us/xamarin/get-started/tutorials/local-database/?tutorial-step=2&tabs=vswin.