Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Update xmldb.md #715

Closed
wants to merge 1 commit into from
Closed

Update xmldb.md #715

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
48 changes: 33 additions & 15 deletions general/development/tools/xmldb.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -74,21 +74,39 @@ Choose the 'View PHP Code' option and then copy and paste the generated code.

Apart from the [Database Structures guidelines](https://docs.moodle.org/dev/Database), some more conventions should be followed:

1. About names:
1. All lowercase names (tables, indexes, keys and fields).
1. Table names and field names must use only a-z, 0-9 and _ chars. Max 28 characters.
1. Key and index names under the XMLDB Files must be formed by concatenating the name of the fields present in the key/index with the '"-" (minus) character.
1. Primary key always must be named "primary" (this is one exception to the previous convention).
1. It's highly recommended to avoid [reserved words](https://docs.moodle.org/dev/XMLDB_reserved_words) completely. We know we have some of them now but they should be completely out for next releases.
1. About NULLS
1. Avoid to create all the fields as NOT NULL with the *silly* default value `*` (empty string). The underlying code used to create tables will handle it properly but the XMLDB structure must be REAL. Read more in the [Problems Page](https://docs.moodle.org/dev/XMLDB_Problems#NOT_NULL_fields_using_a_DEFAULT_*_clause).
1. About FOREIGN KEYS
1. Under the tables of every XMLDB file, you must define the existing **Foreign Keys** (FK) properly. This will allow everybody to know a bit better the structure, allow to evolve to a better constrained system in the future and will provide the underlying code with the needed info to create the proper indexes.
1. Note that, if you define any field combination as FK you won't have to create any index on that fields, the code will do it automatically!
1. Respect Convention 1.3
1. About UNIQUE KEYS
1. Declare any fields as UNIQUE KEY (UK) only if they are going to be used as target for one FK. Create unique indexes instead.
1. Respect Convention 1.3
<ol>
<li>
About names:
<ol style="list-style-type: decimal">
<li>All lowercase names (tables, indexes, keys and fields).</li>
<li>Table names and field names must use only a-z, 0-9 and _ chars. Max 28 characters.</li>
<li>Key and index names under the XMLDB Files must be formed by concatenating the name of the fields present in the key/index with the '"-" (minus) character.</li>
<li>Primary key always must be named "primary" (this is one exception to the previous convention).</li>
<li>It's highly recommended to avoid <a href="https://docs.moodle.org/dev/XMLDB_reserved_words" target="_blank" rel="noopener noreferrer">reserved words</a> completely. We know we have some of them now but they should be completely out for next releases.</li>
</ol>
</li>
<li>
About NULLS
<ol style="list-style-type: decimal">
<li>Avoid to create all the fields as NOT NULL with the <em>silly</em> default value <code>''</code> (empty string). The underlying code used to create tables will handle it properly but the XMLDB structure must be REAL. Read more in the <a href="https://docs.moodle.org/dev/XMLDB_Problems#NOT_NULL_fields_using_a_DEFAULT_.27.27_clause" target="_blank" rel="noopener noreferrer">Problems Page</a>.</li>
</ol>
</li>
<li>
About FOREIGN KEYS
<ol style="list-style-type: decimal">
<li>Under the tables of every XMLDB file, you must define the existing <strong>Foreign Keys</strong> (FK) properly. This will allow everybody to know a bit better the structure, allow to evolve to a better constrained system in the future and will provide the underlying code with the needed info to create the proper indexes.</li>
<li>Note that, if you define any field combination as FK you won't have to create any index on that fields, the code will do it automatically!</li>
<li>Respect Convention 1.3</li>
</ol>
</li>
<li>
About UNIQUE KEYS
<ol style="list-style-type: decimal">
<li>Declare any fields as UNIQUE KEY (UK) only if they are going to be used as target for one FK. Create unique indexes instead.</li>
<li>Respect Convention 1.3</li>
</ol>
</li>
</ol>

## See also

Expand Down
Loading