= IdStringifier
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SPI to convert the identifier (primary key) of an entity, of a given type (eg Integer) into a string, and to convert back again into the key object used to actually look up the target entity instance; supported by both JDO and JPA persistence mechanisms.

This is ultimately used by xref:refguide:applib:index/services/bookmark/BookmarkService.adoc[BookmarkService] where we hold a persistent reference to an entity. The resultant string also appears in URLs of the Wicket viewer and Restful Objects viewers, and in mementos eg in _org.apache.causeway.schema.cmd.v2.CommandDto_ and _org.apache.causeway.schema.ixn.v2.InteractionDto_ .

The framework provides default implementations of this SPI for JDO (data store and application identity) and for JPA. Because this is a SPI, other modules or application code can provide their own implementations. An example of such is the JPA implementation of the `commandlog` extension.

== API

[source,java]
.IdStringifier.java
----
interface IdStringifier<T> {
  public final static char SEPARATOR;
  Class<T> getCorrespondingClass()
  String enstring(T value)     // <.>
  T destring(Class<?> targetEntityClass, String stringified)     // <.>
  boolean isValid(T value)     // <.>
}
----

<.> xref:#enstring_T[enstring(T)]
+
--
Convert the value (which will be of the same type as returned by _#getCorrespondingClass()_ into a string representation.
--
<.> xref:#destring_Class_String[destring(Class, String)]
+
--
Convert a string representation of the identifier (as returned by _#enstring(Object)_ ) into an object that can be used to retrieve.
--
<.> xref:#isValid_T[isValid(T)]
+
--
Whether the non-null primary key object is valid, that is, in the case of a composite, whether it is fully populated.
--

== Members

[#enstring_T]
=== enstring(T)

Convert the value (which will be of the same type as returned by _#getCorrespondingClass()_ into a string representation.

[#destring_Class_String]
=== destring(Class, String)

Convert a string representation of the identifier (as returned by _#enstring(Object)_ ) into an object that can be used to retrieve.

[#isValid_T]
=== isValid(T)

Whether the non-null primary key object is valid, that is, in the case of a composite, whether it is fully populated.
