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Plugins

Under Raven.Database.Plugins namespace various interfaces and classes can be found that might be used to extend the database behavior.

Note

All DLL's containing custom plugins must be placed in Plugins directory that by default are found in ~\Plugins. To change the default location of this directory, please refer to this page.

Triggers

This type of extensions grants the ability to manipulate when certain action is taking place e.g. document is deleted or index is updated.

Triggers can be divided to four categories:
* PUT triggers
* DELETE triggers
* Read triggers
* Index Query triggers
* Index Update triggers

PUT triggers

To create his own trigger, one must inherit from AbstractPutTrigger or AbstractAttachmentPutTrigger, but before we will do that lets take a look at them more closely.

public abstract class AbstractPutTrigger
{
	public virtual VetoResult AllowPut(string key, RavenJObject document, RavenJObject metadata, TransactionInformation transactionInformation)
	{
		return VetoResult.Allowed;
	}

	public virtual void OnPut(string key, RavenJObject document, RavenJObject metadata, TransactionInformation transactionInformation)
	{
	}

	public virtual void AfterPut(string key, RavenJObject document, RavenJObject metadata, Guid etag, TransactionInformation transactionInformation)
	{
	}

	public virtual void AfterCommit(string key, RavenJObject document, RavenJObject metadata, Guid etag)
	{
	}

	public virtual void Initialize()
	{
	}

	public virtual void SecondStageInit()
	{
	}

	public DocumentDatabase Database { get; set; }
}

public abstract class AbstractAttachmentPutTrigger
{
	public virtual VetoResult AllowPut(string key, Stream data, RavenJObject metadata)
	{
		return VetoResult.Allowed;
	}

	public virtual void OnPut(string key, Stream data, RavenJObject metadata)
	{
	}

	public virtual void AfterPut(string key, Stream data, RavenJObject metadata, Guid etag)
	{
	}

	public virtual void AfterCommit(string key, Stream data, RavenJObject metadata, Guid etag)
	{
	}

	public virtual void SecondStageInit()
	{
	}


	public virtual void Initialize()
	{
	}

	public DocumentDatabase Database { get; set; }
}

public class VetoResult
{
	public static VetoResult Allowed
	{
		get { return new VetoResult(true, "allowed"); }
	}

	public static VetoResult Deny(string reason)
	{
		return new VetoResult(false, reason);
	}

	private VetoResult(bool allowed, string reason)
	{
		IsAllowed = allowed;
		Reason = reason;
	}

	public bool IsAllowed { get; private set; }

	public string Reason { get; private set; }
}

where:
* AllowPut is used to grant or deny the put operation.
* OnPut is used to perform any logic just before the document is saved to the disk.
* AfterPut is used to perform any logic after the document was inserted but still in the same transaction as in OnPut method.
* AfterCommit is used to perform any logic after the transaction was commited.
* Initialize and SecondStageInit are used in trigger initialization process.

Example: Security trigger

public class SecurityTrigger : AbstractPutTrigger
{
	public override VetoResult AllowPut(string key, RavenJObject document, RavenJObject metadata, TransactionInformation transactionInformation)
	{
		var doc = Database.Get(key, transactionInformation);
		if (doc == null) // new document
			return VetoResult.Allowed;

		if (doc.Metadata["Document-Owner"] == null)// no security
			return VetoResult.Allowed;

		if (doc.Metadata["Document-Owner"].Value<string>() == Thread.CurrentPrincipal.Identity.Name)
			return VetoResult.Allowed;

		return VetoResult.Deny("You are not the document owner, cannot modify document");
	}

	public override void OnPut(string key, RavenJObject document, RavenJObject metadata, TransactionInformation transactionInformation)
	{
		if (metadata["Document-Owner"] == null) // user didn't explicitly set it
		{
			// modify the metadata to the current user
			metadata["Document-Owner"] = RavenJObject.FromObject(Thread.CurrentPrincipal.Identity.Name);
		}
	}
}

Most of the logic is in AllowPut method, where we check the existing owner (by checking the current version of the document) and reject the update if it if the owner doesn't match. In the OnPut method, we ensure that the metadata we need is setup correctly. To control attachment putting, similar trigger can be created.

DELETE triggers

Delete triggers are similar in shape to the put triggers, but in contrast to them they control the delete operations. To build your own trigger, one must inherit from AbstractDeleteTrigger or AbstractAttachmentDeleteTrigger.

public abstract class AbstractDeleteTrigger
{
	public virtual VetoResult AllowDelete(string key, TransactionInformation transactionInformation)
	{
		return VetoResult.Allowed;
	}

	public virtual void OnDelete(string key, TransactionInformation transactionInformation)
	{
	}

	public virtual void AfterDelete(string key, TransactionInformation transactionInformation)
	{
	}

	public virtual void AfterCommit(string key)
	{
	}

	public virtual void SecondStageInit()
	{
	}


	public virtual void Initialize()
	{
	}

	public DocumentDatabase Database { get; set; }
}

public abstract class AbstractAttachmentDeleteTrigger
{
	public virtual VetoResult AllowDelete(string key)
	{
		return VetoResult.Allowed;
	}

	public virtual void OnDelete(string key)
	{
	}

	public virtual void AfterDelete(string key)
	{
	}

	public virtual void AfterCommit(string key)
	{

	}

	public virtual void SecondStageInit()
	{
	}

	public virtual void Initialize()
	{
	}

	public DocumentDatabase Database { get; set; }
}

where:
* AllowDelete is used to grant or deny the delete operation.
* OnDelete is used to perform any logic just before the document is deleted.
* AfterDelete is used to perform any logic after the document has been deleted but still in the same transaction as in OnDelete method.
* AfterCommit is used to perform any logic after the transaction was commited.
* Initialize and SecondStageInit are used in trigger initialization process.

Example: Cascading deletes

public class CascadeDeleteTrigger : AbstractDeleteTrigger
{
	public override void OnDelete(string key, TransactionInformation txInfo)
	{
		var document = Database.Get(key, txInfo);
		if (document == null)
			return;

		Database.Delete(document.Metadata.Value<string>("Cascade-Delete"), null, txInfo);
	}
}

In this case, we perform another delete operation as part of the current delete operation. This operation is done under the same transaction as the original operation.

Read triggers

Another type of triggers is used to control the access to the documents and manipulate their context when performing read operations. Similar to the previous triggers, two classes were introduced, the AbstractReadTrigger and AbstractAttachmentReadTrigger.

public abstract class AbstractReadTrigger
{
	public virtual ReadVetoResult AllowRead(string key, RavenJObject metadata, ReadOperation operation, TransactionInformation transactionInformation)
	{
		return ReadVetoResult.Allowed;
	}

	public virtual void OnRead(string key, RavenJObject document, RavenJObject metadata, ReadOperation operation, TransactionInformation transactionInformation)
	{
	}

	public virtual void Initialize()
	{
	}

	public virtual void SecondStageInit()
	{
	}

	public DocumentDatabase Database { get; set; }
}

public abstract class AbstractAttachmentReadTrigger
{
	public virtual ReadVetoResult AllowRead(string key, Stream data, RavenJObject metadata, ReadOperation operation)
	{
		return ReadVetoResult.Allowed;
	}

	public virtual void OnRead(string key, Attachment attachment)
	{
	}

	public virtual void OnRead(AttachmentInformation information)
	{
	}

	public virtual void SecondStageInit()
	{
	}

	public virtual void Initialize()
	{
	}

	public DocumentDatabase Database { get; set; }

}

public class ReadVetoResult
{
	public static ReadVetoResult Allowed
	{
		get { return new ReadVetoResult(ReadAllow.Allow, "allowed"); }
	}

	public static ReadVetoResult Ignore
	{
		get { return new ReadVetoResult(ReadAllow.Ignore, "ignore"); }
	}

	public static ReadVetoResult Deny(string reason)
	{
		return new ReadVetoResult(ReadAllow.Deny, reason);
	}

	private ReadVetoResult(ReadAllow allowed, string reason)
	{
		Veto = allowed;
		Reason = reason;
	}

	public ReadAllow Veto { get; private set; }

	public enum ReadAllow
	{
		Allow,
		Deny,
		Ignore
	}

	public string Reason { get; private set; }
}

where:
* AllowRead is used to grant or deny the read operation.
* OnRead is used to perform any logic just before the document is read e.g. modify the document or document metadata (modified values are transient and are not saved to the database).
* Initialize and SecondStageInit are used in trigger initialization process.

Example: Information hiding

public class SecurityReadTrigger : AbstractReadTrigger
{
	public override ReadVetoResult AllowRead(string key, RavenJObject metadata, ReadOperation operation, TransactionInformation transactionInformation)
	{
		if (metadata.Value<string>("Document-Owner") == Thread.CurrentPrincipal.Identity.Name)
			return ReadVetoResult.Allowed;

		if (operation == ReadOperation.Load)
			return ReadVetoResult.Deny("You don't have permission to read this document");

		return ReadVetoResult.Ignore;
	}
}

In the example above, we only let the owner of a document to read it. You can see that a Read trigger can deny the read to the user (returning an error to the user) or ignoring the read (hiding the presence of the document). You can also make decisions based on wheter that specific document was requested, or if the document was read as part of a query.

Example: Linking document on the server side

public class EmbedLinkDocument : AbstractReadTrigger
{
	public override void OnRead(string key, RavenJObject document, RavenJObject metadata, ReadOperation operation, TransactionInformation transactionInformation)
	{
		var linkName = metadata.Value<string>("Raven-Link-Name");
		var link = metadata.Value<string>("Raven-Link");
		if (link == null)
			return;

		var linkedDocument = Database.Get(link, transactionInformation);
		document.Add(linkName, linkedDocument.ToJson());
	}
}

In this case, we detect that a document with a link was requested, and we stitch the document together with its link to create a single document.

Index Query triggers

Query triggers have been introduced to extend the query parsing capabilities and provide users with a way to modify the queries before they are executed against the index. To write your own query trigger, you must inherit from AbstractIndexQueryTrigger class.

public abstract class AbstractIndexQueryTrigger
{
	public virtual void Initialize()
	{
	}

	public virtual void SecondStageInit()
	{
	}


	public DocumentDatabase Database { get; set; }

	public abstract Query ProcessQuery(string indexName, Query query, IndexQuery originalQuery);
}

where:
* ProcessQuery is used to perform any logic on the provided query.
* Initialize and SecondStageInit are used in trigger initialization process.

Example: Combining current query with our additional custom logic

public class CustomQueryTrigger : AbstractIndexQueryTrigger
{
	private const string SpecificIndexName = "Specific/Index";

	public override Query ProcessQuery(string indexName, Query query, IndexQuery originalQuery)
	{
		if (indexName != SpecificIndexName)
			return query;

		var customQuery = new PrefixQuery(new Term("CustomField", "CustomPrefix"));

		return new BooleanQuery
			{
				{ query, Occur.MUST },
				{ customQuery, Occur.MUST}
			};
	}
}

Index Update triggers

Index Update triggers allow users to perform custom actions every time an index entry has been created or deleted. To write your own trigger we must consider two classes. The AbstractIndexUpdateTrigger and AbstractIndexUpdateTriggerBatcher defined below.

public abstract class AbstractIndexUpdateTrigger
{
	public virtual void Initialize()
	{
	}

	public virtual void SecondStageInit()
	{
	}

	public abstract AbstractIndexUpdateTriggerBatcher CreateBatcher(string indexName);

	public DocumentDatabase Database { get; set; }
}

where:
* CreateBatcher is used to construct a batcher for given index.
* Initialize and SecondStageInit are used in trigger initialization process.

public abstract class AbstractIndexUpdateTriggerBatcher
{
	public virtual void OnIndexEntryDeleted(string entryKey)
	{
	}

	public virtual void OnIndexEntryCreated(string entryKey, Document document)
	{
	}

	public virtual void AnErrorOccured(Exception exception)
	{
	}
}

where:
* OnIndexEntryDeleted is executed when index entry is being removed from the index. The provided key may represent an already deleted document.
* OnIndexEntryCreated is executed when specified document with a given key is being inserted. The changes to the provided lucene document will be writen to the Lucene index.
* AnErrorOccured is used to notify the batcher that an error occured.

Example: Creating static snapshot from the indexed document

public class SnapshotShoppingCartUpdateTrigger : AbstractIndexUpdateTrigger
{
	public override AbstractIndexUpdateTriggerBatcher CreateBatcher(string indexName)
	{
		return new SnapshotShoppingCartBatcher(indexName, Database);
	}
}

public class SnapshotShoppingCartBatcher : AbstractIndexUpdateTriggerBatcher
{
	private readonly string indexName;

	private readonly DocumentDatabase database;

	public SnapshotShoppingCartBatcher(string indexName, DocumentDatabase database)
	{
		this.indexName = indexName;
		this.database = database;
	}

	public override void OnIndexEntryCreated(string entryKey, Document document)
	{
		if (indexName != "Aggregates/ShoppingCart")
			return;

		var shoppingCart = RavenJObject.Parse(document.GetField("Aggregate").StringValue);
		var shoppingCartId = document.GetField("Id").StringValue;

		var result = database.Put("shoppingcarts/" + shoppingCartId + "/snapshots/", null, shoppingCart, new RavenJObject(), null);
		document.Add(new Field("Snapshot", result.Key, Field.Store.YES, Field.Index.NOT_ANALYZED));
	}
}

This index works on the following index in order to create a static snapshot of the indexed document whenever it is indexed. Note that we use identity insert here (the key we use ends with '/') so we will have documents like this:

  • shoppingcarts/12/snapshots/1
  • shoppingcarts/12/snapshots/2
  • shoppingcarts/12/snapshots/3

This is nice if we want to keep a record of all the changes to the index. Note that we also change the document to store the snapshot key for this particular version.

Codecs

The AbstractDocumentCodec and AbstractIndexCodec classes have been introduced as an entry point to custom compression methods.

public abstract class AbstractDocumentCodec
{
	public DocumentDatabase Database { get; set; }

	public virtual void Initialize()
	{
	}

	public virtual void SecondStageInit()
	{
	}

	public abstract Stream Encode(string key, RavenJObject data, RavenJObject metadata, Stream dataStream);

	public abstract Stream Decode(string key, RavenJObject metadata, Stream dataStream);
}

public abstract class AbstractIndexCodec
{
	public virtual void Initialize(DocumentDatabase database)
	{
	}

	public virtual void SecondStageInit()
	{
	}

	public abstract Stream Encode(string key, Stream dataStream);

	public abstract Stream Decode(string key, Stream dataStream);
}

where:
* Encode is executed when given document/index is written.
* Decode is executed when provided document/index is read.
* Initialize and SecondStageInit are used in trigger initialization process.

Example: Compression

public class SimpleCompressionCodec : AbstractDocumentCodec
{
	private readonly SimpleCompressor compressor = new SimpleCompressor();

	public override Stream Encode(string key, RavenJObject data, RavenJObject metadata, Stream dataStream)
	{
		return compressor.Compress(key, data, metadata, dataStream);
	}

	public override Stream Decode(string key, RavenJObject metadata, Stream dataStream)
	{
		return compressor.Decompress(key, metadata, dataStream);
	}
}

Example: Encryption

public class SimpleEncryptionCodec : AbstractDocumentCodec
{
	private readonly SimpleEncryptor encryptor = new SimpleEncryptor();

	public override Stream Encode(string key, RavenJObject data, RavenJObject metadata, Stream dataStream)
	{
		return encryptor.Encrypt(key, data, metadata, dataStream);
	}

	public override Stream Decode(string key, RavenJObject metadata, Stream dataStream)
	{
		return encryptor.Decrypt(key, metadata, dataStream);
	}
}

Tasks

Another type of plugins gives us the ability to perform various actions during server/database startup process or enables us to perform actions periodically. For these needs we have introduced two interfaces and one abstract class.

public interface IStartupTask
{
	void Execute(DocumentDatabase database);
}

public interface IServerStartupTask
{
	void Execute(HttpServer server);
}

public abstract class AbstractBackgroundTask : IStartupTask
{
	private static readonly ILog log = LogManager.GetCurrentClassLogger();

	public DocumentDatabase Database { get; set; }

	public void Execute(DocumentDatabase database)
	{
		Database = database;
		Initialize();
		Task.Factory.StartNew(BackgroundTask, TaskCreationOptions.LongRunning);
	}

	protected virtual void Initialize()
	{
	}

	int workCounter;
	public void BackgroundTask()
	{
		var name = GetType().Name;
		var context = Database.WorkContext;
		while (context.DoWork)
		{
			var foundWork = false;
			try
			{
				foundWork = HandleWork();
			}
			catch (Exception e)
			{
				log.ErrorException("Failed to execute background task", e);
			}
			if (foundWork == false)
			{
				context.WaitForWork(TimeoutForNextWork(), ref workCounter, name);
			}
			else
			{
				context.UpdateFoundWork();
			}
		}
	}

	protected virtual TimeSpan TimeoutForNextWork()
	{
		return TimeSpan.FromHours(1);
	}

	protected abstract bool HandleWork();
}

where:
* IStartupTask can be used to implement a task that will be started during database initialization.
* IServerStartupTask can be used to implement a task that will be started during server initialization.
* AbstractBackgroundTask is a base for all periodic tasks.

Example: Send email when server is starting

public class SendEmailWhenServerIsStartingTask : IServerStartupTask
{
	public void Execute(HttpServer server)
	{
		var message = new MailMessage("ravendb@myhost.com", "admin@myhost.com")
			{
				Subject = "RavenDB server started.",
				Body = "Start at: " + DateTime.Now.ToShortDateString()
			};

		using (var smtpClient = new SmtpClient("mail.myhost.com"))
		{
			smtpClient.Send(message);
		}
	}
}

Example: Perform a cleanup task during database initialization

public class CleanupWhenDatabaseIsStarting : IStartupTask
{
	private const string SpecificDatabaseName = "ExampleDB";

	public void Execute(DocumentDatabase database)
	{
		if (database.Name != SpecificDatabaseName)
			return;

		bool stale;
		var queryResults = database.QueryDocumentIds("Notifications/Temp", new IndexQuery(), out stale);

		foreach (var documentId in queryResults)
		{
			database.Delete(documentId, null, null);
		}
	}
}

Example: Perform a cleanup task every six hours

public class RemoveAllTemporaryNotificationsTask : AbstractBackgroundTask
{
	protected override bool HandleWork()
	{
		var queryResults = Database.Query("Notifications/Temp", new IndexQuery());
		foreach (var document in queryResults.Results)
		{
			var id = ((RavenJObject)document["@metadata"]).Value<string>("@id");
			Database.Delete(id, null, null);
		}

		return true;
	}

	protected override TimeSpan TimeoutForNextWork()
	{
		return TimeSpan.FromHours(6);
	}
}

Compilation Extensions

There might be a certian situations when users want to put more complex logic to calculate a value of an index entry field. To do this, in RavenDB, we have introduced an AbstractDynamicCompilationExtension.

public abstract class AbstractDynamicCompilationExtension
{
	public abstract string[] GetNamespacesToImport();

	public abstract string[] GetAssembliesToReference();
}

where:
* GetNamespacesToImport returns a list of namespaces that RavenDB will have to import
* GetAssembliesToReference returns a list of full paths to assemblies

Example: Check if a given word is a palindrome

public static class Palindrome
{
	public static bool IsPalindrome(string word)
	{
		if (string.IsNullOrEmpty(word))
			return true;

		var min = 0;
		var max = word.Length - 1;
		while (true)
		{
			if (min > max)
				return true;

			var a = word[min];
			var b = word[max];
			if (char.ToLower(a) != char.ToLower(b))
				return false;

			min++;
			max--;
		}
	}
}

public class PalindromeDynamicCompilationExtension : AbstractDynamicCompilationExtension
{
	public override string[] GetNamespacesToImport()
	{
		return new[]
			{
				typeof (Palindrome).Namespace
			};
	}

	public override string[] GetAssembliesToReference()
	{
		return new[]
			{
				typeof (Palindrome).Assembly.Location
			};
	}
}

Now we can use our Palindrome in our index definition.

store.DatabaseCommands.PutIndex("Dictionary/Palindromes", new IndexDefinition
	{
		Map = @"from word in docs.Words 
				select new 
				{ 
							Word = word.Value, 
							IsPalindrome = Palindrome.IsPalindrome(word.Value) 
				}"
	});

Analyzer Generators

To add your custom analyzer, one must implement the AbstractAnalyzerGenerator class and provide logic when your custom analyzer should be used.

public abstract class AbstractAnalyzerGenerator
{
	public abstract Analyzer GenerateAnalyzerForIndexing(string indexName, Document document, Analyzer previousAnalyzer);

	public abstract Analyzer GenerateAnalyzerForQuerying(string indexName, string query, Analyzer previousAnalyzer);
}

where:
* GenerateAnalyzerForIndexing returns an analyzer that will be used while performing indexing operation.
* GenerateAnalyzerForQuerying returns an analyzer that will be used while performing querying.

Example: Using different analyzer for specific index

public class CustomAnalyzerGenerator : AbstractAnalyzerGenerator
{
	private const string SpecificIndexName = "Specific/Index";

	public override Analyzer GenerateAnalyzerForIndexing(string indexName, Document document, Analyzer previousAnalyzer)
	{
		if (indexName == SpecificIndexName)
		{
			return new WhitespaceAnalyzer();
		}

		return previousAnalyzer;
	}

	public override Analyzer GenerateAnalyzerForQuerying(string indexName, string query, Analyzer previousAnalyzer)
	{
		if (indexName == SpecificIndexName)
		{
			return new WhitespaceAnalyzer();
		}

		return previousAnalyzer;
	}
}

Database configuration

To alter database configuration you can edit the configuration document (more about how it can be done and what configuration options are available can be found here), but sometimes it might be better to change configuration programatically e.g. imagine a situation, where you have 100 databases and you want to change one setting in every one of them. This is why the IAlterConfiguration interfaces was created.

public interface IAlterConfiguration
{
	void AlterConfiguration(InMemoryRavenConfiguration configuration);
}

Example: Disable compression and extend temp index cleanup period

public class CommonConfiguration : IAlterConfiguration
{
	public void AlterConfiguration(InMemoryRavenConfiguration configuration)
	{
		configuration.HttpCompression = false;
		configuration.TempIndexCleanupPeriod = TimeSpan.FromMinutes(30);
	}
}