Adds Alembic migration for DB/Tables conversion to utf8mb4

MySql defaults to `utf8` and case insensitive collation so migrate these to case sensitive and `utf8mb4`

Closes #21

Signed-off-by: Leonidas Spyropoulos <artafinde@gmail.com>

migrations/versions/56e2ce8e2ffa_utf8mb4_charset_and_collation.py

@@ -0,0 +1,78 @@
+"""utf8mb4 charset and collation
+
+Revision ID: 56e2ce8e2ffa
+Revises: ef39fcd6e1cd
+Create Date: 2021-05-17 14:23:00.008479
+
+"""
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision = '56e2ce8e2ffa'
+down_revision = 'ef39fcd6e1cd'
+branch_labels = None
+depends_on = None
+
+# Tables affected by charset/collate change
+tables = ['AccountTypes', 'ApiRateLimit', 'Bans', 'DependencyTypes', 'Groups', 'Licenses', 'OfficialProviders',
+          'PackageBases', 'PackageBlacklist', 'PackageComments', 'PackageDepends', 'PackageKeywords',
+          'PackageRelations', 'PackageRequests', 'PackageSources', 'Packages', 'RelationTypes', 'RequestTypes',
+          'SSHPubKeys', 'Sessions', 'TU_VoteInfo', 'Terms', 'Users']
+
+# Indexes affected by charset/collate change
+# Map of Unique Indexes key = index_name, value = [table_name, column1, column2]
+indexes = {'ProviderNameProvides': ['OfficialProviders', 'Name', 'Provides']}
+
+# Source charset/collation, before this migration is run.
+src_charset = "utf8"
+src_collate = "utf8_general_ci"
+
+# Destination charset/collation, after this migration is run.
+dst_charset = "utf8mb4"
+dst_collate = "utf8mb4_bin"
+
+
+def rebuild_unique_indexes_with_str_cols():
+    for idx_name in indexes:
+        sql = f"""
+DROP INDEX IF EXISTS {idx_name} 
+ON {indexes.get(idx_name)[0]}
+"""
+        op.execute(sql)
+        sql = f"""
+CREATE UNIQUE INDEX {idx_name} 
+ON {indexes.get(idx_name)[0]} 
+({indexes.get(idx_name)[1]}, {indexes.get(idx_name)[2]}) 
+"""
+        op.execute(sql)
+
+
+def do_all(iterable, fn):
+    for element in iterable:
+        fn(element)
+
+
+def upgrade():
+    def op_execute(table):
+        sql = f"""
+ALTER TABLE {table} 
+CONVERT TO CHARACTER SET {dst_charset} 
+COLLATE {dst_collate}
+"""
+        op.execute(sql)
+
+    do_all(tables, op_execute)
+    rebuild_unique_indexes_with_str_cols()
+
+
+def downgrade():
+    def op_execute(table):
+        sql = f"""
+ALTER TABLE {table} 
+CONVERT TO CHARACTER SET {src_charset} 
+COLLATE {src_collate}
+"""
+        op.execute(sql)
+
+    do_all(tables, op_execute)
+    rebuild_unique_indexes_with_str_cols()