public void Subscribe(IQueryable query)
{
if (null == _dependency)
{
//Get Query Object from IQuery Interface Value...
_objectQuery = QueryExtension.GetObjectQuery <TEntity>(_context, query);
//Get SQL connection string from Query Context...
string connection = QueryExtension.GetConnectionString(_context);
//Get SQL Command from Object Query...
string commandString = QueryExtension.GetSqlString(_objectQuery);
//Register SQL command
using (SqlCommand command = new SqlCommand(commandString, new SqlConnection(connection)))
{
//Open SQL Connection
command.Connection.Open();
command.Notification = null;
command.NotificationAutoEnlist = true;
// Create a dependency and associate it with the SqlCommand.
_dependency = new SqlDependency(command);
_dependency.OnChange += dependency_OnChange;
// Execute the command.
SqlDataReader reader = command.ExecuteReader();
}
}
}
/// <summary>
/// Initializes a new instance of ImmediateNotificationRegister class.
/// </summary>
/// <param name="context">an instance of DbContext is used to get an ObjectQuery object</param>
/// <param name="query">an instance of IQueryable is used to get ObjectQuery object, and then get
/// _connection string and _command string to register SqlDependency nitification. </param>
public SqlNotificationListener(DbContext context, IQueryable query)
{
try
{
this._iquery = query;
_context = context;
// Get the ObjectQuery directly or convert the DbQuery to ObjectQuery.
_oquery = QueryExtension.GetObjectQuery <TEntity>(context, _iquery);
_connection = QueryExtension.GetSqlConnection(_oquery);
_command = QueryExtension.GetSqlCommand(_oquery, _connection);
}
catch (ArgumentException ex)
{
if (ex.ParamName == "context")
{
throw new ArgumentException("Paramter cannot be null", nameof(context), ex);
}
throw new ArgumentException("Paramter cannot be null", nameof(query), ex);
}
catch (Exception ex)
{
throw new Exception(
"Fails to initialize a new instance of SqlNotificationListener class.", ex);
}
}
