/// <summary>
/// 通过主键和指定类型从数据库获取对象
/// </summary>
/// <typeparam name="T">指定类型</typeparam>
/// <param name="keyValue">主键值（通常为Guid），不能为空</param>
/// <returns>从数据库中得到的对象,如果数据库中没找到对象会返回一个空对象</returns>
/// 前置条件
/// 1.keyValue不能为空
/// 2.传入的对象T只能有一个主键
public T GetByKey <T>(object keyValue)
where T : new()
{
PreconditionAssert.IsNotNull(keyValue, ErrorMessages.NullReferenceException);
ORMHelper.EntityIsMappingDatabase(typeof(T), ErrorMessages.EntityMappingError);
SelectCommandCreator dbCommandCreator = new SelectCommandCreator(_dbAccess);
dbCommandCreator.ObjectType = typeof(T);
dbCommandCreator.KeyValue = keyValue;
dbCommandCreator.SelectType = SelectType.GetOneByKeyValue;
DbCommand dbCommand = dbCommandCreator.GetDbCommand();
DataTable dt = _dbAccess.GetDataTableByCommand(dbCommand);
if (dt.Rows.Count == 0)
{
return(default(T));
}
else if (dt.Rows.Count == 1)
{
return(ORMHelper.ConvertDataRowToEntity <T>(dt.Rows[0]));
}
else
{
//引发数据获取结果错误
throw new ORMException(ErrorMessages.ResultNotUniqueMessage);
}
}