Add unique index on user_export_jobs

[kesselb]

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Steps to reproduce

Execute 2x

insert into oc_user_export_jobs (source_user, migrators, status) values ('bob', '[""calendar-app"",""mail_account"",""tables"",""files"",""trashbin"",""account"",""calendar"",""contacts""]', 0);

The original steps to reproduce were repeating the export http request quickly to trigger that database state. I was able to reproduce, but by adding sleep(3) after checkJobAndGetUser / before queueExportJob.

Expected behaviour

Api status request fails hard

{
  "reqId": "30qemcHmWkQrs9dsUsxO",
  "level": 3,
  "time": "2026-03-18T14:44:47+00:00",
  "remoteAddr": "172.18.0.1",
  "user": "bob",
  "app": "no app in context",
  "method": "GET",
  "url": "/ocs/v2.php/apps/user_migration/api/v1/status",
  "scriptName": "/ocs/v2.php",
  "message": "Did not expect more than one result when executing: query \"SELECT * FROM `*PREFIX*user_export_jobs` WHERE `source_user` = :dcValue1\"; ",
  "userAgent": "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/145.0.0.0 Safari/537.36",
  "version": "33.0.0.16",
  "exception": {
    "Exception": "OCP\\AppFramework\\Db\\MultipleObjectsReturnedException",
    "Message": "Did not expect more than one result when executing: query \"SELECT * FROM `*PREFIX*user_export_jobs` WHERE `source_user` = :dcValue1\"; ",
    "Code": 0,
    "Trace": [
      {
        "file": "/var/www/html/lib/public/AppFramework/Db/QBMapper.php",
        "line": 382,
        "function": "findOneQuery",
        "class": "OCP\\AppFramework\\Db\\QBMapper",
        "type": "->",
        "args": [
          {
            "__class__": "OC\\DB\\QueryBuilder\\QueryBuilder"
          }
        ]
      },
      {
        "file": "/var/www/html/apps-writable/user_migration/lib/Db/UserExportMapper.php",
        "line": 46,
        "function": "findEntity",
        "class": "OCP\\AppFramework\\Db\\QBMapper",
        "type": "->",
        "args": [
          {
            "__class__": "OC\\DB\\QueryBuilder\\QueryBuilder"
          }
        ]
      },
      {
        "file": "/var/www/html/apps-writable/user_migration/lib/Service/UserMigrationService.php",
        "line": 481,
        "function": "getBySourceUser",
        "class": "OCA\\UserMigration\\Db\\UserExportMapper",
        "type": "->",
        "args": [
          "bob"
        ]
      },
      {
        "file": "/var/www/html/apps-writable/user_migration/lib/Controller/ApiController.php",
        "line": 67,
        "function": "getCurrentJob",
        "class": "OCA\\UserMigration\\Service\\UserMigrationService",
        "type": "->",
        "args": [
          {
            "__class__": "OC\\User\\User"
          }
        ]
      },
      {
        "file": "/var/www/html/apps-writable/user_migration/lib/Controller/ApiController.php",
        "line": 114,
        "function": "getCurrentJobData",
        "class": "OCA\\UserMigration\\Controller\\ApiController",
        "type": "->",
        "args": [
          {
            "__class__": "OC\\User\\User"
          }
        ]
      },
      {
        "file": "/var/www/html/lib/private/AppFramework/Http/Dispatcher.php",
        "line": 205,
        "function": "status",
        "class": "OCA\\UserMigration\\Controller\\ApiController",
        "type": "->",
        "args": []
      },
      {
        "file": "/var/www/html/lib/private/AppFramework/Http/Dispatcher.php",
        "line": 118,
        "function": "executeController",
        "class": "OC\\AppFramework\\Http\\Dispatcher",
        "type": "->",
        "args": [
          {
            "__class__": "OCA\\UserMigration\\Controller\\ApiController"
          },
          "status"
        ]
      },
      {
        "file": "/var/www/html/lib/private/AppFramework/App.php",
        "line": 153,
        "function": "dispatch",
        "class": "OC\\AppFramework\\Http\\Dispatcher",
        "type": "->",
        "args": [
          {
            "__class__": "OCA\\UserMigration\\Controller\\ApiController"
          },
          "status"
        ]
      },
      {
        "file": "/var/www/html/lib/private/Route/Router.php",
        "line": 321,
        "function": "main",
        "class": "OC\\AppFramework\\App",
        "type": "::",
        "args": [
          "OCA\\UserMigration\\Controller\\ApiController",
          "status",
          {
            "__class__": "OC\\AppFramework\\DependencyInjection\\DIContainer"
          },
          {
            "apiVersion": "1",
            "_route": "ocs.user_migration.api.status"
          }
        ]
      },
      {
        "file": "/var/www/html/ocs/v1.php",
        "line": 61,
        "function": "match",
        "class": "OC\\Route\\Router",
        "type": "->",
        "args": [
          "/ocsapp/apps/user_migration/api/v1/status"
        ]
      },
      {
        "file": "/var/www/html/ocs/v2.php",
        "line": 8,
        "args": [
          "/var/www/html/ocs/v1.php"
        ],
        "function": "require_once"
      }
    ],
    "File": "/var/www/html/lib/public/AppFramework/Db/QBMapper.php",
    "Line": 293,
    "message": "Did not expect more than one result when executing: query \"SELECT * FROM `*PREFIX*user_export_jobs` WHERE `source_user` = :dcValue1\"; ",
    "exception": "{\"class\":\"OCP\\AppFramework\\Db\\MultipleObjectsReturnedException\",\"message\":\"Did not expect more than one result when executing: query \\\"SELECT * FROM `*PREFIX*user_export_jobs` WHERE `source_user` = :dcValue1\\\"; \",\"code\":0,\"file\":\"/var/www/html/lib/public/AppFramework/Db/QBMapper.php:293\",\"trace\":\"#0 /var/www/html/lib/public/AppFramework/Db/QBMapper.php(382): OCP\\AppFramework\\Db\\QBMapper->findOneQuery(Object(OC\\DB\\QueryBuilder\\QueryBuilder))\\n#1 /var/www/html/apps-writable/user_migration/lib/Db/UserExportMapper.php(46): OCP\\AppFramework\\Db\\QBMapper->findEntity(Object(OC\\DB\\QueryBuilder\\QueryBuilder))\\n#2 /var/www/html/apps-writable/user_migration/lib/Service/UserMigrationService.php(481): OCA\\UserMigration\\Db\\UserExportMapper->getBySourceUser('bob')\\n#3 /var/www/html/apps-writable/user_migration/lib/Controller/ApiController.php(67): OCA\\UserMigration\\Service\\UserMigrationService->getCurrentJob(Object(OC\\User\\User))\\n#4 /var/www/html/apps-writable/user_migration/lib/Controller/ApiController.php(114): OCA\\UserMigration\\Controller\\ApiController->getCurrentJobData(Object(OC\\User\\User))\\n#5 /var/www/html/lib/private/AppFramework/Http/Dispatcher.php(205): OCA\\UserMigration\\Controller\\ApiController->status()\\n#6 /var/www/html/lib/private/AppFramework/Http/Dispatcher.php(118): OC\\AppFramework\\Http\\Dispatcher->executeController(Object(OCA\\UserMigration\\Controller\\ApiController), 'status')\\n#7 /var/www/html/lib/private/AppFramework/App.php(153): OC\\AppFramework\\Http\\Dispatcher->dispatch(Object(OCA\\UserMigration\\Controller\\ApiController), 'status')\\n#8 /var/www/html/lib/private/Route/Router.php(321): OC\\AppFramework\\App::main('OCA\\\\UserMigrati...', 'status', Object(OC\\AppFramework\\DependencyInjection\\DIContainer), Array)\\n#9 /var/www/html/ocs/v1.php(61): OC\\Route\\Router->match('/ocsapp/apps/us...')\\n#10 /var/www/html/ocs/v2.php(8): require_once('/var/www/html/o...')\\n#11 {main}\"}",
    "CustomMessage": "Did not expect more than one result when executing: query \"SELECT * FROM `*PREFIX*user_export_jobs` WHERE `source_user` = :dcValue1\"; "
  }
}

Actual behaviour

Enforce that there's only one export job by adding a unique constraint or make the service more relaxed.