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Purpose: db_changes.php returns an array of injection rules the installer uses to insert small snippets into core files. Each rule must match the target file's exact marker text.

Format

 'relative/path/to/file.php',
    'marker_code' => 'exact text to find',
    'hook_code'   => 'code to insert',
    'position'    => 'before' | 'after' | 'replace'
  ],
  ...
];

Example A — Inject , users.user_something after users.user_verified in the long $get_profile SELECT

 'profile.php',    // change to actual file path that contains the SELECT
        'marker_code' => "users.user_verified,",
        'hook_code'   => " users.user_something",
        'position'    => 'after'
    ],
    // Example B follows...
];

Why this works: the marker "users.user_verified," is matched exactly; the installer inserts the hook text immediately after, producing:

..., users.user_verified, users.user_something, users.user_subscribed, ...

Example B — Inject , user_picture after user_verified in the $get_users SELECT

 'profile.php',
        'marker_code' => "users.user_verified,",
        'hook_code'   => " users.user_something",
        'position'    => 'after'
    ],

    // this rule injects user_picture
    [
        'target_file' => 'includes/class-user.php', // change to actual file path for the get_users query
        'marker_code' => "user_verified",
        'hook_code'   => ", user_picture",
        'position'    => 'after'
    ]
];

Result example:

SELECT ... user_subscribed, user_verified, user_picture
FROM users
...

Best practices / gotchas

• Exact match required: copy-paste the marker substring exactly as it appears (including comma/space).
• Prefer short, unique markers (e.g. "users.user_verified," rather than just "verified").
• Multiline SQL: match a fragment that sits on a single line (avoid matching across newlines).
• Comma handling: if marker already ends with a comma, inject without an extra comma; if not, include the leading comma in hook_code.
• Multiple occurrences: if the marker appears more than once, injection may affect the first match — make marker more specific if needed.
• Test on staging: installer creates backups but always verify before production.