Contents Id

Extension Title

Contents Id

Introduction

This extension assigns a unique integer identifier to tables defined in the contents. Allows foreign key referencing to a contents (text based primary key) by an integer identifier. This extension is required because the gpkg_contents table "rowid table" rowid values are "not persistent and might change".

"If the rowid is not aliased by INTEGER PRIMARY KEY then it is not persistent and might change. In particular the VACUUM command will change rowids for tables that do not declare an INTEGER PRIMARY KEY. Therefore, applications should not normally access the rowid directly, but instead use an INTEGER PRIMARY KEY."

Extension Author

National Geospatial-Intelligence Agency, author_name nga

Extension Name or Template

nga_contents_id

Extension Type

New Requirement

Applicability

This extension applies to the table names of tables defined in the contents (1.1.3).

Scope

Read-write

Requirements

GeoPackage

Extension Table Entry

The Contents Id extension is registered into the gpkg_extensions table only once as follows:

`gpkg_extensions`
table_name	column_name	extension_name	definition	scope
null	null	`nga_contents_id`	URL to this extension description	read-write

Contents Id Table

The Contents Id Table contains an integer id and contents table name.

`nga_contents_id`
Column Name	Type	Description	Null	Default	Key
`id`	INTEGER	Autoincrement primary key	no		PK
`table_name`	TEXT	The name of the actual content table, foreign key to `gpkg_contents`	no		FK,UK


CREATE TABLE nga_contents_id (
  id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
  table_name TEXT NOT NULL,
  CONSTRAINT uk_nci_table_name UNIQUE (table_name),
  CONSTRAINT fk_nci_gc_tn FOREIGN KEY (table_name) REFERENCES gpkg_contents(table_name)
);

Contents Entry

The Contents Id Table defines a Contents row (2.4.2). This is required for use in the Related Tables Extension.

`gpkg_contents`
table_name	data_type	identifier	description	last_change	min_x	min_y	max_x	max_y	srs_id
nga_contents_id	gpkg_extensions	nga_contents_id		date of last change

GeoPackage SQLite Configuration

None

GeoPackage SQLite Extension

None

Examples

The rivers GeoPackage has a contents id for the rivers feature table.

The example GeoPackage has contents id entries for all feature tables.