MySQL通过实例化对象参数查询实例讲解

public static string QueryByEntity<T>(T t) where T : new()
{ string resultstr = string.Empty;
 MySqlDataReader reader = null; try
 {
 Type type = typeof(T);
 PropertyInfo[] properties = type.GetProperties(); string select = string.Format("Select * from {0} {1}", type.Name, "{0}"); string where = string.Empty; foreach (PropertyInfo property in properties)
 { var value = t.GetPropertyValue<T>(property); if (value != null && !value.Equals(property.GetDefaultValue()))
 { if (string.IsNullOrEmpty(where))
 { where = string.Format(" where {0}='{1}' ", property.Name, value);
 } else
 { where = string.Format(" {0} and {1} = '{2}' ", where, property.Name, value);
 }
 }
 } select = string.Format(select, where);
 
 MySqlConnection connection = OpenConnection(); if (connection == null) return resultstr;
 MySqlCommand _sqlCom = new MySqlCommand(select, connection);
 reader = _sqlCom.ExecuteReader();
 List<T> tList = new List<T>(); while (reader.Read())
 {
 T t1 = new T(); foreach (PropertyInfo property in properties)
 { if (!string.IsNullOrEmpty(reader[property.Name].ToString()))
 {
 property.SetMethod.Invoke(t1, new object[] { reader[property.Name] });
 }
 }
 tList.Add(t1);
 }
 resultstr = JsonConvert.SerializeObject(tList);
 } catch (Exception ex)
 {
 Logging.Error(string.Format("查询数据库失败，{0}", ex.Message));
 } finally
 { if (reader != null)
 {
 reader.Close();
 reader.Dispose();
 }
 } return resultstr;
}internal static class ObjectExtend
{ public static object GetPropertyValue<T>(this object obj, PropertyInfo property)
 {
 Type type = typeof(T);
 PropertyInfo propertyInfo = type.GetProperty(property.Name); if (propertyInfo != null)
 { return propertyInfo.GetMethod.Invoke(obj, null);
 } return null;
 } public static object GetDefaultValue(this PropertyInfo property)
 { return property.PropertyType.IsValueType ? Activator.CreateInstance(property.PropertyType) : null;
 }
}