"""为 SearchFilter 的 title / first_author / first_author_institution 三列建 pg_trgm GIN 索引。

原因:DRF SearchFilter 走 `column ILIKE '%keyword%'` 前后通配,B-tree 索引救不了;
高频关键词 + 几十万行表会 30s+ timeout。pg_trgm 给 trigram 建 GIN 索引,
ILIKE '%xxx%' 走索引,降到几十 ms。

pg_trgm 是 PostgreSQL contrib 扩展,首次启用需要 DB superuser 权限;
CREATE EXTENSION IF NOT EXISTS 幂等,迁移可安全重跑。
"""
from django.db import migrations


class Migration(migrations.Migration):

    dependencies = [
        ('resm', '0005_alter_paper_fetch_status'),
    ]

    operations = [
        migrations.RunSQL(
            sql=[
                "CREATE EXTENSION IF NOT EXISTS pg_trgm;",
                "CREATE INDEX IF NOT EXISTS paper_title_trgm "
                "ON resm_paper USING gin (title gin_trgm_ops);",
                "CREATE INDEX IF NOT EXISTS paper_first_author_trgm "
                "ON resm_paper USING gin (first_author gin_trgm_ops);",
                "CREATE INDEX IF NOT EXISTS paper_first_author_institution_trgm "
                "ON resm_paper USING gin (first_author_institution gin_trgm_ops);",
            ],
            reverse_sql=[
                "DROP INDEX IF EXISTS paper_first_author_institution_trgm;",
                "DROP INDEX IF EXISTS paper_first_author_trgm;",
                "DROP INDEX IF EXISTS paper_title_trgm;",
                # pg_trgm 扩展不 drop —— 其他 app / 表可能也在用
            ],
        ),
    ]