Interface of connection handler

will be extended later on with async variants if needed

Author: alex-kulakov

Orm/Xtensive.Orm/Orm/ConnectionErrorEventData.cs

@@ -0,0 +1,24 @@
+using System;
+using System.Data.Common;
+using Xtensive.Core;
+
+namespace Xtensive.Orm
+{
+  /// <summary>
+  /// Extended <see cref="ConnectionEventData"/> with error happend during connection opening, restoration or initialization.
+  /// </summary>
+  public class ConnectionErrorEventData : ConnectionEventData
+  {
+    /// <summary>
+    /// The exception appeared.
+    /// </summary>
+    public Exception Exception { get; }
+
+    public ConnectionErrorEventData(Exception exception, DbConnection connection, bool reconnect = false)
+      : base(connection, reconnect)
+    {
+      ArgumentValidator.EnsureArgumentNotNull(exception, nameof(exception));
+      Exception = exception;
+    }
+  }
+}

Orm/Xtensive.Orm/Orm/ConnectionEventData.cs

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+using System.Data.Common;
+using Xtensive.Core;
+
+namespace Xtensive.Orm
+{
+  /// <summary>
+  /// Contains general data for <see cref="IConnectionHandler"/> methods.
+  /// </summary>
+  public class ConnectionEventData
+  {
+    /// <summary>
+    /// The connection for which event triggered.
+    /// </summary>
+    public DbConnection Connection { get; }
+
+    /// <summary>
+    /// Indicates whether event happened during an attempt to restore connection.
+    /// </summary>
+    public bool Reconnect { get; }
+
+    public ConnectionEventData(DbConnection connection, bool reconnect = false)
+    {
+      ArgumentValidator.EnsureArgumentNotNull(connection, nameof(connection));
+      Connection = connection;
+      Reconnect = reconnect;
+    }
+  }
+}

Orm/Xtensive.Orm/Orm/ConnectionInitEventData.cs

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+using System.Data.Common;
+using Xtensive.Core;
+
+namespace Xtensive.Orm
+{
+  /// <summary>
+  /// Extended <see cref="ConnectionEventData"/> with connection initialization script
+  /// </summary>
+  public class ConnectionInitEventData : ConnectionEventData
+  {
+    /// <summary>
+    /// Gets the script which will be used for connection initializatin
+    /// </summary>
+    public string InitializationScript { get; }
+
+    public ConnectionInitEventData(string initializationScript, DbConnection connection, bool reconnect = false)
+      : base(connection, reconnect)
+    {
+      ArgumentValidator.EnsureArgumentNotNullOrEmpty(initializationScript, nameof(initializationScript));
+      InitializationScript = initializationScript;
+    }
+  }
+}

Orm/Xtensive.Orm/Orm/Interfaces/IConnectionHandler.cs

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+namespace Xtensive.Orm
+{
+  /// <summary>
+  /// Offers event-like methods to access native database connection on different stages
+  /// </summary>
+  public interface IConnectionHandler
+  {
+    /// <summary>
+    /// Executes before connection opening.
+    /// </summary>
+    /// <param name="eventData">Information connected with this event.</param>
+    void ConnectionOpening(ConnectionEventData eventData) { }
+
+    /// <summary>
+    /// Executes when connection is already opened but initialization script
+    /// hasn't been executed yet.
+    /// </summary>
+    /// <param name="eventData">Information connected with this event.</param>
+    void ConnectionInitialization(ConnectionInitEventData eventData) { }
+
+    /// <summary>
+    /// Executes when connection is successfully opened and initialized
+    /// </summary>
+    /// <param name="eventData">Information connected with this event</param>
+    void ConnectionOpened(ConnectionEventData eventData) { }
+
+    /// <summary>
+    /// Executes if an error appeared on either connection opening or connection initialization.
+    /// </summary>
+    /// <param name="eventData">Information connected with this event</param>
+    void ConnectionOpeningFailed(ConnectionErrorEventData eventData) { }
+  }
+}