对PostgreSQL源代码中的 ObjectClass的初步理解

/*                            
 * 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;                            

/*                    
 * 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 */
}                    

/*                                    
 * 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++;                                
}