How can indexes be checked if they exist in a Laravel migration?

问题

Trying to check if a unique index exists on a table when preparing a migration, how can it be achieved?

Schema::table('persons', function (Blueprint $table) {
    if ($table->hasIndex('persons_body_unique')) {
        $table->dropUnique('persons_body_unique');
    }
})

Something that looks like the above. (apparently, hasIndex() doesn't exist)

回答1:

Using "doctrine-dbal" that Laravel uses is better solution:

Schema::table('persons', function (Blueprint $table) {
    $sm = Schema::getConnection()->getDoctrineSchemaManager();
    $indexesFound = $sm->listTableIndexes('persons');

    if(array_key_exists("persons_body_unique", $indexesFound))
        $table->dropUnique("persons_body_unique");
})

回答2:

The mysql query

SHOW INDEXES FROM persons

will give you back all of the indexes on the table, however it includes additional info other than just the names. In my setup, the column containing the name is called Key_name so lets get a collection of key names

collect(DB::select("SHOW INDEXES FROM persons"))->pluck('Key_name')

And since its a collection you can use contains so finally we have:

if (collect(DB::select("SHOW INDEXES FROM persons"))->pluck('Key_name')->contains('persons_body_unique')) {
        $table->dropUnique('persons_body_unique');
}

来源：https://stackoverflow.com/questions/45882990/how-can-indexes-be-checked-if-they-exist-in-a-laravel-migration