Database handler globally as Singleton pattern in xamarin forms - xamarin

Question

I am developing an application which have a local database for offline support. So I am using Sqlite.net.pcl plugin and its working fine for all Create, Insert, Update and Delete table for every class model.
But instead of creating a separate database activities like insert, get, update for each Model class, I tried to worked on singeton pattern of common database handler(DatabasHandler.cs).
This is my code which I tried to workout singleton pattern,
public void CreateTable<T>() where T : new()
{
var myClass = new T();
myDatabase.CreateTableAsync<T>().Wait();
}
I called this function from my EmployeeViewModel class like this;
App.Database.CreateTable<EmployeeModel>();
here EmployeeModel is a model class and its worked fine, also the above function is successfully created a Employee Table. Doing the same way I created rest of the Tables from each ViewModel like this;
App.Database.CreateTable<SalaryModel>(); // call from SalaryViewModel Page
App.Database.CreateTable<EmployeeAttendanceModel>(); // call from AttendanceViewModel Page
Next: So how can I insert and get all list items into DatabaseHandler.cs using same (Create Table)singleton pattern. My question is;
How should I create a method for Insert/Get/Update a list in DatabaseHandler.cs(Singleton class)?
How should I call those method(Insert/Get/Update) from its viewmodel?
Please help me,

Answer 1

Now I had a similar thing in my Old XF app this is how I implemented the Singleton this will also answer your first question:
How should I create a method for Insert/Get/Update a list in DatabaseHandler.cs(Singleton class)?
public class DatabaseHandler: IDisposable
{
private SQLiteConnection conn;
//public static string sqlpath;
private bool disposed = false;
private static readonly Lazy<DatabaseHandler> database = new Lazy<DatabaseHandler>(() => new DatabaseHandler());
private DatabaseHandler() { }
public static DatabaseHandler Database
{
get
{
return database.Value;
}
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (disposed)
return;
if (disposing)
{
Dispose();
}
disposed = true;
}
public bool InitDatabase()
{
var ifExist = true;
try
{
this.CreateDatabase();
ifExist = TableExists(nameof(LocationModel), conn);
if (!ifExist)
this.CreateTable<LocationModel>();
return true;
}
catch (Exception ex)
{
return false;
}
}
public static bool TableExists(String tableName, SQLiteConnection connection)
{
var cmd = connection.CreateCommand("SELECT name FROM sqlite_master WHERE type = 'table' AND name = #name", new object[] { tableName });
//cmd.CommandText = "SELECT * FROM sqlite_master WHERE type = 'table' AND name = #name";
//cmd.Parameters.Add("#name", DbType.String).Value = tableName;
string tabledata = cmd.ExecuteScalar<string>();
return (cmd.ExecuteScalar<string>() != null);
}
public SQLiteConnection GetConnection()
{
var sqliteFilename = "xamdblocal.db3";
string documentsPath = Environment.GetFolderPath(Environment.SpecialFolder.Personal); // Documents folder
var path = Path.Combine(documentsPath, sqliteFilename);
Console.WriteLine(path);
if (!File.Exists(path)) File.Create(path);
//var plat = new SQLite.Net.Platform.XamarinAndroid.SQLitePlatformAndroid();
var conn = new SQLiteConnection(path);
// Return the database connection
return conn;
}
private bool CreateDatabase()
{
conn = GetConnection();
string str = conn.DatabasePath;
return true;
}
public bool CreateTable<T>()
where T : new()
{
conn.DropTable<T>();
conn.CreateTable<T>();
return true;
}
public bool InsertIntoTable<T>(T LoginData)
where T : new()
{
conn.Insert(LoginData);
return true;
}
public bool InsertBulkIntoTable<T>(IList<T> LoginData)
where T : class //new()
{
conn.InsertAll(LoginData);
return true;
}
public List<T> SelectDataFromTable<T>()
where T : new()
{
try
{
return conn.Table<T>().ToList();
}
catch (Exception ex)
{
return null;
}
}
public List<T> SelectTableDatafromQuery<T>(string query)
where T : new()
{
return conn.Query<T>(query, new object[] { })
.ToList();
}
public bool UpdateTableData<T>(string query)
where T : new()
{
conn.Query<T>(query);
return true;
}
public void UpdateTableData<T>(IEnumerable<T> query)
where T : new()
{
conn.UpdateAll(query);
}
public void UpdateTableData<T>(T query)
where T : new()
{
conn.Update(query);
}
public bool DeleteTableData<T>(T LoginData)
{
conn.Delete(LoginData);
return true;
}
public bool DeleteTableDataFromPrimaryKey<T>(object primaryKey)
{
conn.Delete(primaryKey);
return true;
}
public bool DeleteTableDataFromQuery<T>(string query)
where T : new()
{
conn.Query<T>(query);
return true;
}
}
How should I call those method(Insert/Get/Update) from its viewmodel? Please help me,
Now for Eg: you want to insert location's Lat Long in your local database where your local model looks something like this:
public class LocationModel
{
[AutoIncrement, PrimaryKey]
public int Id { get; set; }
public double Latitude { get; set; }
public double Longitude { get; set; }
public string Address { get; set; }
}
So first what you will do is create an instance of LocationModel something like this:
var locationModel = new LocationModel
{
Latitude = location.Latitude,
Longitude = location.Longitude
};
Then insert it something like this:
DatabaseHandler.Database.InsertIntoTable<LocationModel>(locationModel);
Also, do not forget to add the SQLiteNetExtensions in your project for Linq support.
Goodluck feel free to revert in case of queries