public void Downgrade(IRepository repository, int version)
{
int dbVersion = GetDbVersion(repository);
if (dbVersion <= version)
{
// Already lower or same as current version.
return;
}
if (version < 0)
{
throw new SectorException("Version cannot be less than 0");
}
// Example downgrade from 4 back to 0:
// 4_downgrade set version to 3
// 3_downgrade set version to 2,
// 2_downgrade set version to 1
// 1_downgrade set version = 0
// Means we need to go over range 1, 4 in reverse order, here we iterate
// over range 1, 4 reversed to { 4, 1 } == 4, 3, 2, 1 and end with dbVersion 0
int steps = dbVersion - version;
foreach (var downVersion in Enumerable.Range(version + 1, steps).Reverse())
{
using (var transaction = sectorDb.Connection.BeginTransaction())
{
using (var sqlCommand = sectorDb.Connection.CreateCommand())
{
// Run the SQL for the next version.
sqlCommand.CommandText = repository.GetDowngradeSql(downVersion);
sqlCommand.ExecuteNonQuery();
}
// Now update the version table.
using (var sqlCommand = sectorDb.Connection.CreateCommand())
{
// Upgrade the version info.
const string templ = "UPDATE {0} SET version = @RepoVer WHERE repository_id = @RepoId";
sqlCommand.CommandText = string.Format(templ, SectorDb.TableName);
{
var param = sqlCommand.CreateParameter();
param.DbType = DbType.String;
param.ParameterName = "@RepoId";
param.Value = repository.RepositoryId;
sqlCommand.Parameters.Add(param);
}
{
var param = sqlCommand.CreateParameter();
param.DbType = DbType.Int32;
param.ParameterName = "@RepoVer";
param.Value = downVersion - 1;
sqlCommand.Parameters.Add(param);
}
sqlCommand.ExecuteNonQuery();
}
transaction.Commit();
}
}
}