Editing WikiDB/Defining tables

WikiDB is a tool to create and query database-like data from within your wiki.

This page describes how to add structure to your data.

== Basic principles ==

=== Tables ====

* You need to define one ore more 'table' namespaces, in <code>LocalSettings.php</code>.
* Any page in a table namespace is a table definition, which is referred to by its page name (e.g. <code><nowiki>[[Table:People]]</nowiki></code>).
* The content of each page in a table namespace defines the schema for a specific table.
* When referring to tables, the namespace prefix is only required if there are multiple table namespaces (and even then, only in some situations).
* Creating redirects within a table namespace allows you to set up alternative names for tables.  The most common use for this is to allow you to rename/move a table without having to update all existing data definitions to use the new name.

=== Data in tables ====

* Data exists independently of any table structure, which has a number of important implications:
** No structure is required - you can assign data to a table without the table page even existing.
** The structure can change at any time, and all existing data is immediately updated appropriately.
** All schema changes are non-destructive, i.e. they don't modify data.  For example, unlike in most database systems, converting a string field to an integer won't destroy all non-integer values that may exist for that field.
** As a corollary to the above: all schema changes are reversible.  Changing that integer back to a string will restore all data to its original state.
* Any field you define will cause all data in that field to be formatted/validated/sorted according to the data-type (including any relevant options) that you specify.
** For example, non-numeric values in a field defined as <code>integer</code> will be considered invalid and be treated as blank.
* Any field for which there is some data but no definition will be treated as a <code>wikistring</code> field.
* The list of data types [[WikiDB/Tutorial: Creating your own data type|is extensible]] (i.e. you can create your own types).
* You can define field aliases, so if half the pages on your wiki describe People using a <code>LastName</code> field, and half use a <code>Surname</code> field, then you can simply set up an alias so both are treated as equivalent.