%Library.PersistentXEPhidden abstract persistent class %Library.PersistentXEP
Extends the %Persistent Interface for XEP generated classes.
If a persistent class uses %Storage.Persistent then the USEEXTENTSET parameter is used to specify the global naming strategy used by the default storage class (
%Storage.Persistent). If TRUE, then global names are generated for each index that is not already allocated a LOCATION in the active storage definition.
If the storage definition specifies EXTENTLOCATION then that value is used as the base reference for all globals assigned to indices that do not have an explicit LOCATION assigned.
The global name generator for USEEXTENTSET = TRUE honors the package prefix defined in the Package Definition. If none is defined then the package prefix is generated using a based-62 encoded integer produced from CRC32 of the package name. The specific class identifier is generated from the unqualified class name using the same hash (class->crc32->base62) to form EXTENTLOCATION. Specific index suffixes are produced using a generated offset that is local to the first persistent class with an enumerated extent in which the index appears (either defined or inherited).
There are several factors that influence the generation of EXTENTLOCATION:
The EXTENTLOCATION value is used as the base for specific globals allocated to indices. Each index is assigned an offset that is incremented from 1 by 1, offset = 1 is reserved for the IDKEY index.
- If the EXTENTLOCATION keyword is defined then its value is used,
- If the DEFAULTGLOBAL class parameter is defined then its value is used,
- otherwise, the value is generated as two dot delimited segments. The first segment is either the defined package prefix retrieved from the package definition global or, if none is defined, a hash of the package name. The second segment is generated by a hash of the unqualified class name. The hash used is a base 62 encoded CRC32 of the value. For example, Sample.Person produces ^EW3K.wPC9 if no package prefix is defined.
EXTENTLOCATION is specific to each class. When a persistent class extends another persistent class, forming a subextent, then the subclass's EXTENTLOCATION is specific to that subclass. The index location for any inherited index is already defined specifically in the super class so the subclass's EXTENTLOCATION will only be used as the base for any index that originates in the subclass. For example, Sample.Employee extends Sample.Person. The EXTENTLOCATION generated for Sample.Person is ^EW3K.wPC9 and the EXTENTLOCATION for Sample.Employee is ^EW3K.D1Ex. Since Sample.Employee inherits several indices from Sample.Person, the global name assigned to each of those indices is already defined and inherited by Sample.Employee. However, any index defined in Sample.Employee and not inherited from Sample.Person will be assigned a global name based on Sample.Employee's EXTENTLOCATION, not on Sample.Person's EXTENTLOCATION. In other words, the EXTENTLOCATION storage keyword is not inherited.
The following tables show the indices and locations for Sample.Person and Sample.Employee. Notice the last index in the Sample.Employee table:
Class = Sample.Person
Index Location IDKEY ^EW3K.wPC9.1 $Person ^EW3K.wPC9.2 NameIDX ^EW3K.wPC9.3 SSNKey ^EW3K.wPC9.4 ZipCode ^EW3K.wPC9.5 Class = Sample.Employee extends Sample.Person
Index Location IDKEY ^EW3K.wPC9.1 $Person ^EW3K.wPC9.2 NameIDX ^EW3K.wPC9.3 SSNKey ^EW3K.wPC9.4 ZipCode ^EW3K.wPC9.5 $Employee ^EW3K.D1Ex.2
Any generated global index locations and EXTENTLOCATION are updated back into the active storage definition after the class is compiled.
If USEEXTENTSET is FALSE, then global names are generated using the package-hash.class-hashSuffix strategy. For example, ^Sample.PersonD and ^Sample.PersonI("SSNKey") are globals used by Sample.Person and specific index structures are all stored in ^Sample.PersonI with the index name used as the first subscript.