处理 DBNull 的通用方法

发布于 2024-12-14 19:50:55 字数 905 浏览 8 评论 0原文

使用 SqlDataReader 时，我的代码中有很多此类逻辑有没有更干净、更通用的方法来处理这个问题？

 if (reader["VisitingAddressId"] != DBNull.Value)
 {
     visitingAddress = new Address()
     {
         AddressId = Convert.ToInt64(reader["VisitingAddressId"]),
         Address1 = reader["VisitingAddress"].ToString(),
         AddressType = AddressType.VisitingAddress,
         PostalCode = reader["VisitingPostal"].ToString(),
         PostalDistrict = reader["VisitingPostalDistrict"].ToString()
      };
  }

 if (reader["PostalAddressId"] != DBNull.Value)
 {
     postalAddress = new Address()
     {
         AddressId = Convert.ToInt64(reader["PostalAddressId"]),
         Address1 = reader["PostalAddress"].ToString(),
         AddressType = AddressType.PostalAddress,
         PostalCode = reader["PostalPostal"].ToString(),
         PostalDistrict = reader["PostalPostalDistrict"].ToString()
      };
  }

原文

I have a lot of this type of logic in my code when using the SqlDataReader
Is there a cleaner more generic way to handle this?

 if (reader["VisitingAddressId"] != DBNull.Value)
 {
     visitingAddress = new Address()
     {
         AddressId = Convert.ToInt64(reader["VisitingAddressId"]),
         Address1 = reader["VisitingAddress"].ToString(),
         AddressType = AddressType.VisitingAddress,
         PostalCode = reader["VisitingPostal"].ToString(),
         PostalDistrict = reader["VisitingPostalDistrict"].ToString()
      };
  }

 if (reader["PostalAddressId"] != DBNull.Value)
 {
     postalAddress = new Address()
     {
         AddressId = Convert.ToInt64(reader["PostalAddressId"]),
         Address1 = reader["PostalAddress"].ToString(),
         AddressType = AddressType.PostalAddress,
         PostalCode = reader["PostalPostal"].ToString(),
         PostalDistrict = reader["PostalPostalDistrict"].ToString()
      };
  }

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始终不够 2024-12-21 19:50:55

我在数据服务类中有这些辅助方法（您可以将它们设为静态）：

    public T CastDBValue<T>(object value)
    {
        return MapValue<T>(value);
    }   

    internal static T MapValue<T>(object value)
    {
        try
        {
            T result;
            result = value == DBNull.Value ? default(T) : (T)value;
            return result;
        }
        catch (InvalidCastException cex)
        {
            logger.ErrorFormat("Invalid cast while mapping db value '{0}' to type {1}. Error: {2}", value, typeof(T).Name, cex);
            throw new InvalidCastException(string.Format("Invalid cast while mapping db value '{0}' to type {1}. Error: {2}", value, typeof(T).Name, cex.Message));
        }
    }

然后在映射代码中，您只需执行以下操作：

AddressId = dataService.CastDBValue<int>(reader["AddressId"]));
if (AddressId > 0) { ... }

I have these helper methods in a data service class (you could make them both static):

    public T CastDBValue<T>(object value)
    {
        return MapValue<T>(value);
    }   

    internal static T MapValue<T>(object value)
    {
        try
        {
            T result;
            result = value == DBNull.Value ? default(T) : (T)value;
            return result;
        }
        catch (InvalidCastException cex)
        {
            logger.ErrorFormat("Invalid cast while mapping db value '{0}' to type {1}. Error: {2}", value, typeof(T).Name, cex);
            throw new InvalidCastException(string.Format("Invalid cast while mapping db value '{0}' to type {1}. Error: {2}", value, typeof(T).Name, cex.Message));
        }
    }

Then in your mapping code, you just do:

AddressId = dataService.CastDBValue<int>(reader["AddressId"]));
if (AddressId > 0) { ... }

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猫瑾少女 2024-12-21 19:50:55

您可以使用像 Dapper 这样的微型 ORM：http://code.google.com/ p/dapper-dot-net/

多重映射功能将消除所有样板代码。

db.Query<Post,Address,Address,Post>("select * from Posts left join Address ... etc", 
 (post,vaddress,paddress) => 
  {
     post.VisitingAddress = vaddress; 
     post.PostalAddress = paddress; 
     return post; 
   });

You could use a micro-ORM like Dapper: http://code.google.com/p/dapper-dot-net/

The multi mapping functionality would eliminate all that boiler plate code.

db.Query<Post,Address,Address,Post>("select * from Posts left join Address ... etc", 
 (post,vaddress,paddress) => 
  {
     post.VisitingAddress = vaddress; 
     post.PostalAddress = paddress; 
     return post; 
   });

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