对PostgreSQL源代码中的 ObjectClass的初步理解
[作者：技术者高健@博客园 mail: [email protected] ]
depency.h 中：
/* * This enum covers all system catalogs whose OIDs can appear in * pg_depend.classId or pg_shdepend.classId. */ typedef enum ObjectClass { OCLASS_CLASS, /* pg_class */ OCLASS_PROC, /* pg_proc */ OCLASS_TYPE, /* pg_type */ OCLASS_CAST, /* pg_cast */ OCLASS_COLLATION, /* pg_collation */ OCLASS_CONSTRAINT, /* pg_constraint */ OCLASS_CONVERSION, /* pg_conversion */ OCLASS_DEFAULT, /* pg_attrdef */ OCLASS_LANGUAGE, /* pg_language */ OCLASS_LARGEOBJECT, /* pg_largeobject */ OCLASS_OPERATOR, /* pg_operator */ OCLASS_OPCLASS, /* pg_opclass */ OCLASS_OPFAMILY, /* pg_opfamily */ OCLASS_AMOP, /* pg_amop */ OCLASS_AMPROC, /* pg_amproc */ OCLASS_REWRITE, /* pg_rewrite */ OCLASS_TRIGGER, /* pg_trigger */ OCLASS_SCHEMA, /* pg_namespace */ OCLASS_TSPARSER, /* pg_ts_parser */ OCLASS_TSDICT, /* pg_ts_dict */ OCLASS_TSTEMPLATE, /* pg_ts_template */ OCLASS_TSCONFIG, /* pg_ts_config */ OCLASS_ROLE, /* pg_authid */ OCLASS_DATABASE, /* pg_database */ OCLASS_TBLSPACE, /* pg_tablespace */ OCLASS_FDW, /* pg_foreign_data_wrapper */ OCLASS_FOREIGN_SERVER, /* pg_foreign_server */ OCLASS_USER_MAPPING, /* pg_user_mapping */ OCLASS_DEFACL, /* pg_default_acl */ OCLASS_EXTENSION, /* pg_extension */ MAX_OCLASS /* MUST BE LAST */ } ObjectClass;
而dependency.c 中又有如此的代码，看下：
[作者：技术者高健@博客园 mail: [email protected] ]
/* * This constant table maps ObjectClasses to the corresponding catalog OIDs. * See also getObjectClass(). */ static const Oid object_classes[MAX_OCLASS] = { RelationRelationId, /* OCLASS_CLASS */ ProcedureRelationId, /* OCLASS_PROC */ TypeRelationId, /* OCLASS_TYPE */ CastRelationId, /* OCLASS_CAST */ CollationRelationId, /* OCLASS_COLLATION */ ConstraintRelationId, /* OCLASS_CONSTRAINT */ ConversionRelationId, /* OCLASS_CONVERSION */ AttrDefaultRelationId, /* OCLASS_DEFAULT */ LanguageRelationId, /* OCLASS_LANGUAGE */ LargeObjectRelationId, /* OCLASS_LARGEOBJECT */ OperatorRelationId, /* OCLASS_OPERATOR */ OperatorClassRelationId, /* OCLASS_OPCLASS */ OperatorFamilyRelationId, /* OCLASS_OPFAMILY */ AccessMethodOperatorRelationId, /* OCLASS_AMOP */ AccessMethodProcedureRelationId, /* OCLASS_AMPROC */ RewriteRelationId, /* OCLASS_REWRITE */ TriggerRelationId, /* OCLASS_TRIGGER */ NamespaceRelationId, /* OCLASS_SCHEMA */ TSParserRelationId, /* OCLASS_TSPARSER */ TSDictionaryRelationId, /* OCLASS_TSDICT */ TSTemplateRelationId, /* OCLASS_TSTEMPLATE */ TSConfigRelationId, /* OCLASS_TSCONFIG */ AuthIdRelationId, /* OCLASS_ROLE */ DatabaseRelationId, /* OCLASS_DATABASE */ TableSpaceRelationId, /* OCLASS_TBLSPACE */ ForeignDataWrapperRelationId, /* OCLASS_FDW */ ForeignServerRelationId, /* OCLASS_FOREIGN_SERVER */ UserMappingRelationId, /* OCLASS_USER_MAPPING */ DefaultAclRelationId, /* OCLASS_DEFACL */ ExtensionRelationId /* OCLASS_EXTENSION */ }
可以看到上述两段代码，几乎是一行一行对应的。对于其目的，再看如下的代码：
/* * Add an entry to an ObjectAddresses array. * * It is convenient to specify the class by ObjectClass rather than directly * by catalog OID. */ static void add_object_address(ObjectClass oclass, Oid objectId, int32 subId, ObjectAddresses *addrs) { ObjectAddress *item; /* enlarge array if needed */ if (addrs->numrefs >= addrs->maxrefs) { addrs->maxrefs *= 2; addrs->refs = (ObjectAddress *) repalloc(addrs->refs, addrs->maxrefs * sizeof(ObjectAddress)); Assert(!addrs->extras); } /* record this item */ item = addrs->refs + addrs->numrefs; item->classId = object_classes[oclass]; item->objectId = objectId; item->objectSubId = subId; addrs->numrefs++; }
比如，当我用 的oclass 为 OCLASS_SCHEMA 的时候，我通过
item->classId = object_classes[oclass]; 得到的 classId 就是 NamespaceRelationId
再者，当我用 的oclass 为 OCLASS_TRIGGER 的时候，我通过
item->classId = object_classes[oclass]; 得到的 classId 就是 TriggerRelationId
[作者：技术者高健@博客园 mail: [email protected] ]