Make a query overridable.

[masato-hi]

• If implement to the migrate function, make returnable to Report.
• Make allow override multiple queries for a migration.

For example, it is possible to support Cassandra's CQL by implementing the following.

#[derive(Debug)]
struct CassandraConnection;

#[async_trait]
impl AsyncMigrate for CassandraConnection {
    fn assert_migrations_table_query(migration_table_name: &str) -> String {
        const ASSERT_MIGRATIONS_TABLE_QUERY: &'static str = r#"
            CREATE TABLE IF NOT EXISTS %MIGRATION_TABLE_NAME%(
                version INT,
                name TEXT,
                applied_on TEXT,
                checksum TEXT,
                PRIMARY KEY(version)
            )
        "#;
        ASSERT_MIGRATIONS_TABLE_QUERY.replace("%MIGRATION_TABLE_NAME%", migration_table_name)
    }

    fn get_last_applied_migration_query(migration_table_name: &str) -> String {
        const GET_LAST_APPLIED_MIGRATION_QUERY: &'static str = r#"
            SELECT version, name, applied_on, checksum
            FROM %MIGRATION_TABLE_NAME%
        "#;
        GET_LAST_APPLIED_MIGRATION_QUERY.replace("%MIGRATION_TABLE_NAME%", migration_table_name)
    }

    fn get_applied_migrations_query(migration_table_name: &str) -> String {
        const GET_APPLIED_MIGRATIONS_QUERY: &'static str = r#"
            SELECT version, name, applied_on, checksum
            FROM %MIGRATION_TABLE_NAME%;
        "#;
        GET_APPLIED_MIGRATIONS_QUERY.replace("%MIGRATION_TABLE_NAME%", migration_table_name)
    }

    async fn get_last_applied_migration(
        &mut self,
        migration_table_name: &str,
    ) -> Result<Option<Migration>, Error> {
        let mut migrations = self
            .query(Self::get_last_applied_migration_query(migration_table_name).as_str())
            .await
            .migration_err("error getting last applied migration", None)?;

        migrations.sort_by_key(|m| m.version());

        Ok(migrations.pop())
    }

    async fn get_applied_migrations(
        &mut self,
        migration_table_name: &str,
    ) -> Result<Vec<Migration>, Error> {
        let mut migrations = self
            .query(Self::get_applied_migrations_query(migration_table_name).as_str())
            .await
            .migration_err("error getting applied migrations", None)?;

        migrations.sort_by_key(|m| m.version());

        Ok(migrations)
    }
}