see on GitHub

Metadata change listeners

Implement and register IMetadataChangeListener if you want to provide custom logic when file metadata was changed in a session and the metadata update operation is executed. The interface looks as follow:

public interface IMetadataChangeListener
{
	/// <summary>
	/// Invoked before the written data is sent to the server.
	/// </summary>
	/// <param name="instance">The file to affect</param>
	/// <param name="metadata">The new metadata</param>
	/// <param name="original">The original remote object metadata</param>
	/// <returns>
	/// Whatever the metadata was modified and requires us to re-send it.
	/// Returning false would mean that any request of write to the file would be 
	/// ignored in the current SaveChanges call.
	/// </returns>
	bool BeforeChange(FileHeader instance, RavenJObject metadata, RavenJObject original);

	/// <summary>
	/// Invoked after the metadata is sent to the server.
	/// </summary>
	/// <param name="instance">The updated file information.</param>
	/// <param name="metadata">The current metadata as stored in the server.</param>
	void AfterChange(FileHeader instance, RavenJObject metadata);
}

The same like for delete operations you can prevent from updating metadata by returning false from BeforeChange method. The operation will be skipped then and AfterChange won't be executed.

Example

You can modify the metadata before it will be sent to the server. For example you can remove tags that are banned:

public class RemoveBannedTagsListener : IMetadataChangeListener
{
	private readonly string[] bannedTags =
	{
		/* ... */
	};

	public bool BeforeChange(FileHeader instance, RavenJObject metadata, RavenJObject original)
	{
		var tags = metadata.Value<RavenJArray>("Tags");

		if (tags == null)
			return true;

		foreach (var banned in bannedTags)
		{
			tags.Remove(banned);
		}

		metadata["Tags"] = tags; 

		return true;
	}

	public void AfterChange(FileHeader instance, RavenJObject metadata)
	{
		
	}
}