Merge pull request #2515 from owncloud/10.4-e12dbbe-683

[10.4] [PR 683] Release notes foreign keys

modules/admin_manual/pages/release_notes.adoc

@@ -559,6 +559,47 @@ Version 10.1 delivers all the prerequisites to be compatible with the Microsoft
 
 ownCloud Server 10.1 introduces WebDAV Locks that allow clients to lock and unlock resources to prevent other users from making changes. The feature has been implemented as a prerequisite for manual file locking and MS Office Online Server compatibility. In the current state, file locking is only available via API. Users can recognize locked files via the "lock" icon in the file list. Additionally a lock owner (the user who locked the file) can manually unlock them via the "Locks" tab in the right sidebar. The "Locks" tab will only appear for files that have active locks.
 
+=== Foreign Keys in Database
+
+Please note that foreign keys have been added with the :xref:webdav-locks[WebDAV Locks] feature.
+This is the first time ownCloud implements foreign keys.
+
+==== How Does This Affect Each Database
+
+===== MySQL
+
+MySQL supports foreign keys. 
+They are enabled by default.
+
+===== MariaDB
+
+MariaDB supports foreign keys. 
+They are enabled by default.
+
+===== PostgreSQL
+
+PostgreSQL supports foreign keys. 
+They are enabled by default.
+
+===== SQLite
+
+Foreign keys are, by default, disabled in SQLite. 
+You must ensure that foreign keys are enabled in your SQLite installation.
+Here is what https://sqlite.org/foreignkeys.html[the current documentation] says about enabling foreign key support:
+
+[quote,Enabling Foreign Key Support]
+To enable foreign key support, the library must be compiled with neither `SQLITE_OMIT_FOREIGN_KEY` or `SQLITE_OMIT_TRIGGER` defined.
+If `SQLITE_OMIT_TRIGGER` is defined but `SQLITE_OMIT_FOREIGN_KEY` is not, then SQLite behaves as it did prior to version 3.6.19 (2009-10-14) - foreign key definitions are parsed and may be queried using PRAGMA foreign_key_list, but foreign key constraints are not enforced.
+The PRAGMA foreign_keys command is a no-op in this configuration.
+If `SQLITE_OMIT_FOREIGN_KEY` is defined, then foreign key definitions cannot even be parsed (attempting to specify a foreign key definition is a syntax error).
+
+IMPORTANT: SQLite is not recommended for production deployments.
+
+===== Oracle
+
+Oracle supports foreign keys. 
+They are enabled by default.
+
 === Federation: Compliance with proposed OpenCloudMesh 1.0 specification
 
 Federation enables instances of ownCloud and other supporting platforms to exchange information. It allows users to share data across installations building a worldwide collaboration network of decentralized nodes - each under the full control of it's provider. Together with the other vendors the underlying OpenCloudMesh API specification has been shifted to a new level to clean up the interface, improve its stability and to set the foundation for future feature improvements. ownCloud Server 10.1 is compliant with the new specification proposal. The introduction of the new specification does not involve changes in functionality for users.