io.permazen

Class ExportContext

java.lang.Object

io.permazen.ExportContext

public class ExportContext
extends Object

Context for exporting plain (POJO) objects from a JTransaction.

Plain objects (POJO's) can be exported from a JTransaction to the extent that the Permazen model class and the corresponding target POJO class share the same properties. The simplest example of this is when the Permazen model class is also the POJO class (implying a non-abstract class; see also @PermazenType.autogenNonAbstract()). Also possible are POJO classes and model classes that implement common Java interfaces.

The POJO corresponding to an exported database object is supplied by the configured objectMapper. If objectMapper returns null, the database object is not exported, and nulls replace any copied references to it. If objectMapper is null, the default behavior is to create a new POJO using the model class' default constructor, which of course implies the model class cannot be abstract.

Instances ensure that an already-exported database object will be recognized and not exported twice. The objectMapper is invoked at most once for any object ID.

When a database objext is exported, its fields are copied to the POJO. Fields for which no corresponding POJO property exists are omitted.

Reference fields are traversed and the referenced objects are automatically exported as POJO's, recursively. In other words, the entire transitive closure of objects reachable from an exported object is exported. Cycles in the graph of references are handled properly.

Conversion Details

Counter fields export to any Number property. Collection fields export to an existing collection, so that a setter method is not required; however, if the getter returns null, a setter is required and the export will attempt to use an appropriate collection class (HashSet for property of type Set, TreeSet for a property of type SortedSet, etc). To avoid potential mismatch with collection types, initialize collection properties.

See Also:

ImportContext

Constructor Summary

Constructors

Constructor and Description
ExportContext(JTransaction jtx) Constructor.
ExportContext(JTransaction jtx, Function<ObjId,Object> objectMapper) Constructor.

Method Summary

Modifier and Type	Method and Description
Object	exportPlain(JObject jobj) Export a JObject as a plain Java object, along with all other objects reachable from it via copied reference fields.
Object	exportPlain(ObjId id) Export the JObject with the given ObjId as a plain Java object, along with all other objects reachable from it via copied reference fields.
Map<ObjId,Object>	getJObjectMap() Get the mapping from already exported database object to the corresponding POJO.
JTransaction	getTransaction() Get the transaction from which objects are exported.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ExportContext

public ExportContext(JTransaction jtx)

Constructor.

Uses a default objectMapper that creates new exported objects using the default constructor of the model class.

Parameters:

jtx - the transaction from which to export objects

Throws:

IllegalArgumentException - if jtx is null

ExportContext

public ExportContext(JTransaction jtx,
                     Function<ObjId,Object> objectMapper)

Constructor.

Parameters:

jtx - the transaction from which to export objects

objectMapper - function returning the POJO used to export a database object (or null to skip the corresponding object)

Throws:

IllegalArgumentException - if either parameter is null

Method Detail

getTransaction

public JTransaction getTransaction()

Get the transaction from which objects are exported.

Returns:

associated transaction

getJObjectMap

public Map<ObjId,Object> getJObjectMap()

Get the mapping from already exported database object to the corresponding POJO.

Returns:

mapping from exported database object ID to corresponding POJO

exportPlain

public Object exportPlain(JObject jobj)

Export a JObject as a plain Java object, along with all other objects reachable from it via copied reference fields.

Equivalent to exportPlain(jobj.getObjId()).

Parameters:

jobj - object to export; must not be null

Returns:

exported object, or null if the objectMapper returned null for jobj.getObjId()

Throws:

DeletedObjectException - if id refers to an object that does not exist in the transaction associated with this instance

TypeNotInSchemaVersionException - if jobj is an UntypedJObject

IllegalArgumentException - if jobj is null

exportPlain

public Object exportPlain(ObjId id)

Export the JObject with the given ObjId as a plain Java object, along with all other objects reachable from it via copied reference fields.

If the JObject has already been exported, the previously returned Object is returned.

Parameters:

id - object ID of the object to export; must not be null

Returns:

exported object, or null if the objectMapper returned null for id

Throws:

DeletedObjectException - if id refers to an object that does not exist in the transaction associated with this instance

TypeNotInSchemaVersionException - if id refers to a type that does not exist in this instance's transaction's schema version

IllegalArgumentException - if id is null