com.db4o.config

Interface CommonConfiguration

All Known Implementing Classes:

CommonConfigurationImpl

public interface CommonConfiguration

Common configuration methods, applicable for embedded, client and server use of db4o.

In Client/Server use it is good practice to configure the client and the server in exactly the same way.

Since:

7.5

Method Summary

Methods

Modifier and Type	Method and Description
int	activationDepth() gets the configured activation depth.
void	activationDepth(int depth) sets the activation depth to the specified value.
void	add(ConfigurationItem configurationItem) adds ConfigurationItems to be applied when an ObjectContainer or ObjectServer is opened.
void	addAlias(Alias alias) adds a new Alias for a class, namespace or package.
void	allowVersionUpdates(boolean flag) turns automatic database file format version updates on.
void	automaticShutDown(boolean flag) turns automatic shutdown of the engine on and off.
void	bTreeNodeSize(int size) configures the size of BTree nodes in indexes.
void	callbacks(boolean flag) turns callback methods on and off.
void	callConstructors(boolean flag) advises db4o to try instantiating objects with/without calling constructors.
void	detectSchemaChanges(boolean flag) tuning feature: configures whether db4o checks all persistent classes upon system startup, for added or removed fields.
DiagnosticConfiguration	diagnostic() returns the configuration interface for diagnostics.
EnvironmentConfiguration	environment()
void	exceptionsOnNotStorable(boolean flag) configures whether Exceptions are to be thrown, if objects can not be stored.
void	internStrings(boolean flag) configures db4o to call #intern() on strings upon retrieval.
void	markTransient(java.lang.String attributeName) allows to mark fields as transient with custom annotations/attributes.
int	maxStackDepth() gets the configured max stack depth.
void	maxStackDepth(int maxStackDepth) Sets the max stack depth that will be used for recursive storing and activating an object.
void	messageLevel(int level) sets the detail level of db4o messages.
void	nameProvider(NameProvider provider) Registers a NameProvider that assigns a custom name to the database to be used in Object.toString().
ObjectClass	objectClass(java.lang.Object clazz) returns an ObjectClass object to configure the specified class.
boolean	optimizeNativeQueries() indicates whether Native Queries will be optimized dynamically.
void	optimizeNativeQueries(boolean optimizeNQ) If set to true, db4o will try to optimize native queries dynamically at query execution time, otherwise it will run native queries in unoptimized mode as SODA evaluations.
void	outStream(java.io.PrintStream outStream) Assigns a PrintStream where db4o is to print its event messages.
QueryConfiguration	queries() returns the Query configuration interface.
void	reflectWith(Reflector reflector) configures the use of a specially designed reflection implementation.
void	registerTypeHandler(TypeHandlerPredicate predicate, TypeHandler4 typeHandler) allows registering special TypeHandlers for customized marshalling and customized comparisons.
void	removeAlias(Alias alias) Removes an alias previously added with addAlias(Alias).
void	stringEncoding(StringEncoding encoding) configures the string encoding to be used.
void	testConstructors(boolean flag) tuning feature: configures whether db4o should try to instantiate one instance of each persistent class on system startup.
void	updateDepth(int depth) specifies the global updateDepth.
void	weakReferenceCollectionInterval(int milliseconds) configures the timer for WeakReference collection.
void	weakReferences(boolean flag) turns weak reference management on or off.

Method Detail

addAlias

void addAlias(Alias alias)

adds a new Alias for a class, namespace or package.

Aliases can be used to persist classes in the running application to different persistent classes in a database file or on a db4o server.

Two simple Alias implementations are supplied along with db4o:
- TypeAlias provides an #equals() resolver to match names directly.
- WildcardAlias allows simple pattern matching with one single '*' wildcard character.

It is possible to create own complex Alias constructs by creating own resolvers that implement the Alias interface.

Examples of concrete usecases:

// Creating an Alias for a single class
EmbeddedConfiguration config = Db4oEmbedded.newConfiguration(); config.common().addAlias(
new TypeAlias("com.f1.Pilot", "com.f1.Driver"));


// Mapping a Java package onto another
config.common().addAlias(
new WildcardAlias(
"com.f1.*",
"com.f1.client*"));


Aliases that translate the persistent name of a class to a name that already exists as a persistent name in the database (or on the server) are not permitted and will throw an exception when the database file is opened.

Aliases should be configured before opening a database file or connecting to a server.

In client/server environment it is good practice to configure the client and the server in exactly the same way.

removeAlias

void removeAlias(Alias alias)

Removes an alias previously added with addAlias(Alias).

Parameters:

alias - the alias to remove

activationDepth

void activationDepth(int depth)

sets the activation depth to the specified value.

Why activation?
When objects are instantiated from the database, the instantiation of member objects needs to be limited to a certain depth. Otherwise a single object could lead to loading the complete database into memory, if all objects where reachable from a single root object.

db4o uses the concept "depth", the number of field-to-field hops an object is away from another object. The preconfigured "activation depth" db4o uses in the default setting is 5.

Whenever an application iterates through the ObjectSet of a query result, the result objects will be activated to the configured activation depth.

A concrete example with the preconfigured activation depth of 5:

 // Object foo is the result of a query, it is delivered by the ObjectSet 
 Object foo = objectSet.next();

foo.member1.member2.member3.member4.member5 will be a valid object
foo, member1, member2, member3 and member4 will be activated
member5 will be deactivated, all of it's members will be null
member5 can be activated at any time by calling ObjectContainer#activate(member5, depth).

Note that raising the global activation depth will consume more memory and have negative effects on the performance of first-time retrievals. Lowering the global activation depth needs more individual activation work but can increase performance of queries.

ObjectContainer#deactivate(Object, depth) can be used to manually free memory by deactivating objects.

In client/server environment it is good practice to configure the client and the server in exactly the same way.

Parameters:

depth - the desired global activation depth.

See Also:

configuring classes individually

activationDepth

int activationDepth()

gets the configured activation depth.

Returns:

the configured activation depth.

add

void add(ConfigurationItem configurationItem)

adds ConfigurationItems to be applied when an ObjectContainer or ObjectServer is opened.

Parameters:

configurationItem - the ConfigurationItem

allowVersionUpdates

void allowVersionUpdates(boolean flag)

turns automatic database file format version updates on.

Upon db4o database file format version changes, db4o can automatically update database files to the current version. db4objects does not provide functionality to reverse this process. It is not ensured that updated database files can be read with older db4o versions. In some cases (Example: using ObjectManager) it may not be desirable to update database files automatically therefore automatic updating is turned off by default for security reasons.

Call this method to turn automatic database file version updating on.

If automatic updating is turned off, db4o will refuse to open database files that use an older database file format.

In client/server environment it is good practice to configure the client and the server in exactly the same way.

automaticShutDown

void automaticShutDown(boolean flag)

turns automatic shutdown of the engine on and off. The default and recommended setting is true.

Parameters:

flag - whether db4o should shut down automatically.

bTreeNodeSize

void bTreeNodeSize(int size)

configures the size of BTree nodes in indexes.

Default setting: 100
Lower values will allow a lower memory footprint and more efficient reading and writing of small slots.
Higher values will reduce the overall number of read and write operations and allow better performance at the cost of more RAM use.

In client/server environment it is good practice to configure the client and the server in exactly the same way.

Parameters:

size - the number of elements held in one BTree node.

callbacks

void callbacks(boolean flag)

turns callback methods on and off.

Callbacks are turned on by default.

A tuning hint: If callbacks are not used, you can turn this feature off, to prevent db4o from looking for callback methods in persistent classes. This will increase the performance on system startup.

In a client/server environment it is good practice to configure the client and the server in exactly the same way.

Parameters:

flag - false to turn callback methods off

See Also:

Using callbacks

callConstructors

void callConstructors(boolean flag)

advises db4o to try instantiating objects with/without calling constructors.

Not all JDKs / .NET-environments support this feature. db4o will attempt, to follow the setting as good as the enviroment supports. In doing so, it may call implementation-specific features like sun.reflect.ReflectionFactory#newConstructorForSerialization on the Sun Java 1.4.x/5 VM (not available on other VMs) and FormatterServices.GetUninitializedObject() on the .NET framework (not available on CompactFramework). This setting may also be overridden for individual classes in ObjectClass.callConstructor(boolean).

The default setting depends on the features supported by your current environment.

In a client/server environment it is good practice to configure the client and the server in exactly the same way.

Parameters:

flag - - specify true, to request calling constructors, specify false to request not calling constructors.

See Also:

ObjectClass.callConstructor(boolean)

detectSchemaChanges

void detectSchemaChanges(boolean flag)

tuning feature: configures whether db4o checks all persistent classes upon system startup, for added or removed fields.

If this configuration setting is set to false while a database is being created, members of classes will not be detected and stored.

This setting can be set to false in a production environment after all persistent classes have been stored at least once and classes will not be modified any further in the future.

In a client/server environment it is good practice to configure the client and the server in exactly the same way.

Default value:
true

Parameters:

flag - the desired setting

diagnostic

DiagnosticConfiguration diagnostic()

returns the configuration interface for diagnostics.

Returns:

the configuration interface for diagnostics.

exceptionsOnNotStorable

void exceptionsOnNotStorable(boolean flag)

configures whether Exceptions are to be thrown, if objects can not be stored.

db4o requires the presence of a constructor that can be used to instantiate objects. If no default public constructor is present, all available constructors are tested, whether an instance of the class can be instantiated. Null is passed to all constructor parameters. The first constructor that is successfully tested will be used throughout the running db4o session. If an instance of the class can not be instantiated, the object will not be stored. By default, execution will be stopped with an Exception. This method can be used to configure db4o to not throw an ObjectNotStorableException if an object can not be stored.

The default for this setting is true.

In a client/server environment it is good practice to configure the client and the server in exactly the same way.

Parameters:

flag - true to throw Exceptions if objects can not be stored.

internStrings

void internStrings(boolean flag)

configures db4o to call #intern() on strings upon retrieval. In a client/server environment it is good practice to configure the client and the server in exactly the same way.

Parameters:

flag - true to intern strings

markTransient

void markTransient(java.lang.String attributeName)

allows to mark fields as transient with custom annotations/attributes.

.NET only: Call this method with the attribute name that you wish to use to mark fields as transient. Multiple transient attributes are possible by calling this method multiple times with different attribute names.

In a client/server environment it is good practice to configure the client and the server in exactly the same way.

Parameters:

attributeName - - the fully qualified name of the attribute, including it's namespace

messageLevel

void messageLevel(int level)

sets the detail level of db4o messages. Messages will be output to the configured output PrintStream.

Level 0 - no messages
Level 1 - open and close messages
Level 2 - messages for new, update and delete
Level 3 - messages for activate and deactivate

When using client-server and the level is set to 0, the server will override this and set it to 1. To get around this you can set the level to -1. This has the effect of not returning any messages.

In client-server environment this setting can be used on client or on server depending on which information do you want to track (server side provides more detailed information).

Parameters:

level - integer from 0 to 3

See Also:

TODO: replace int with enumeration

objectClass

ObjectClass objectClass(java.lang.Object clazz)

returns an ObjectClass object to configure the specified class.

The clazz parameter can be any of the following:
- a fully qualified classname as a String.
- a Class object.
- any other object to be used as a template.

Parameters:

clazz - class name, Class object, or example object.

Returns:

an instance of an ObjectClass object for configuration.

optimizeNativeQueries

void optimizeNativeQueries(boolean optimizeNQ)

If set to true, db4o will try to optimize native queries dynamically at query execution time, otherwise it will run native queries in unoptimized mode as SODA evaluations. On the Java platform the jars needed for native query optimization (db4o-X.x-nqopt.jar, bloat-X.x.jar) have to be on the classpath at runtime for this switch to have effect.

The default setting is true.

In a client/server environment it is good practice to configure the client and the server in exactly the same way.

Parameters:

optimizeNQ - true, if db4o should try to optimize native queries at query execution time, false otherwise

optimizeNativeQueries

boolean optimizeNativeQueries()

indicates whether Native Queries will be optimized dynamically.

Returns:

boolean true if Native Queries will be optimized dynamically.

See Also:

optimizeNativeQueries(boolean)

queries

QueryConfiguration queries()

returns the Query configuration interface.

reflectWith

void reflectWith(Reflector reflector)

configures the use of a specially designed reflection implementation.

db4o internally uses java.lang.reflect.* by default. On platforms that do not support this package, customized implementations may be written to supply all the functionality of the interfaces in the com.db4o.reflect package. This method can be used to install a custom reflection implementation.

In client-server environment this setting should be used on both the client and the server side (reflector class must be available)

outStream

void outStream(java.io.PrintStream outStream)

Assigns a PrintStream where db4o is to print its event messages.

Messages are useful for debugging purposes and for learning to understand, how db4o works. The message level can be raised with Configuration.messageLevel(int) to produce more detailed messages.

Use outStream(System.out) to print messages to the console.

In client-server environment this setting should be used on the same side where Configuration.messageLevel(int) is used.

Parameters:

outStream - the new PrintStream for messages.

See Also:

messageLevel(int)

stringEncoding

void stringEncoding(StringEncoding encoding)

configures the string encoding to be used.

The string encoding can not be changed in the lifetime of a database file. To set up the database with the correct string encoding, this configuration needs to be set correctly before a database file is created with the first call to Db4oEmbedded.openFile(com.db4o.config.EmbeddedConfiguration, java.lang.String) or com.db4o.cs.Db4oClientServer#openServer.

For subsequent open calls, db4o remembers built-in string encodings. If a custom encoding is used (an encoding that is not supplied from within the db4o library), the correct encoding needs to be configured correctly again for all subsequent calls that open database files.

In a client-server mode, the server and all clients need to have the same string encoding.



Example:
config.stringEncoding(StringEncodings.utf8()));

See Also:

StringEncodings

testConstructors

void testConstructors(boolean flag)

tuning feature: configures whether db4o should try to instantiate one instance of each persistent class on system startup.

In a production environment this setting can be set to false, if all persistent classes have public default constructors.

In a client/server environment it is good practice to configure the client and the server in exactly the same way.

Default value:
true

Parameters:

flag - the desired setting

updateDepth

void updateDepth(int depth)

specifies the global updateDepth.

see the documentation of ObjectContainer.store(java.lang.Object) for further details.

The value be may be overridden for individual classes.

The default setting is 1: Only the object passed to ObjectContainer.store(java.lang.Object) will be updated.

In a client/server environment it is good practice to configure the client and the server in exactly the same way.

Parameters:

depth - the depth of the desired update.

See Also:

ObjectClass.updateDepth(int), ObjectClass.cascadeOnUpdate(boolean), Using callbacks

weakReferences

void weakReferences(boolean flag)

turns weak reference management on or off.

This method must be called before opening a database.

Performance may be improved by running db4o without using weak references durring memory management at the cost of higher memory consumption or by alternatively implementing a manual memory management scheme using ExtObjectContainer.purge(java.lang.Object)

Setting the value to false causes db4o to use hard references to objects, preventing the garbage collection process from disposing of unused objects.

The default setting is true.

weakReferenceCollectionInterval

void weakReferenceCollectionInterval(int milliseconds)

configures the timer for WeakReference collection.

The default setting is 1000 milliseconds.

Configure this setting to zero to turn WeakReference collection off.

Parameters:

milliseconds - the time in milliseconds

registerTypeHandler

void registerTypeHandler(TypeHandlerPredicate predicate,
                       TypeHandler4 typeHandler)

allows registering special TypeHandlers for customized marshalling and customized comparisons.

Parameters:

predicate - to specify for which classes and versions the TypeHandler is to be used.

typeHandler - to be used for the classes that match the predicate.

environment

EnvironmentConfiguration environment()

See Also:

Environment

nameProvider

void nameProvider(NameProvider provider)

Registers a NameProvider that assigns a custom name to the database to be used in Object.toString().

maxStackDepth

void maxStackDepth(int maxStackDepth)

Sets the max stack depth that will be used for recursive storing and activating an object.

The default value is set to Const4.DEFAULT_MAX_STACK_DEPTH

On Android platform, we recomend setting this to 2.

Parameters:

depth - the desired max stack depth.

maxStackDepth

int maxStackDepth()

gets the configured max stack depth.

Returns:

the configured max stack depth.