C＃的性能增益，从一个SqlDataReader返回一个空类型 [英] C# Performance gain returning a Nullable Type from a SqlDataReader

问题描述

我有一个从DataReader返回一个空Int32，而不是建在GetInt32等的简单方法。

我调用这个方法很多很多次，并有一种情况在那里任何时候我可以剃掉，这将是有益的。

任何人都可以提出任何替代方案，并得到一个空Int32出的DataReader的更快的方式？

 私人的Int32？ GetNullableInt32（SqlDataReader的DataReader的，诠释字段索引）
 {
的回报！dataReader.IsDBNull（字段索引）？ 
 dataReader.GetInt32（字段索引）：（？Int32）已空; 
} 
  

解决方案

我的显得的回顾，它有时可以更快地获得价值作为对象，然后检查，如果这是为DBNull。

 私人INT32？ GetNullableInt32（SqlDataReader的DataReader的，INT字段索引）
 {
对象值= dataReader.GetValue（字段索引）; 
返回值是DBNull的？ （？Int32）已空（Int32）已值; 
} 
  

它至少值得一试。请注意，这是假设你可以直接拆箱到 INT ...我不知道自己是否这是正确的，但它会很容易看到的。

现在还有另一种方法是少了几分安全的 - 它会返回null任何非整数值，即使字段实际上是一个字符串，例如：

 私人的Int32？ GetNullableInt32（SqlDataReader的DataReader的，INT字段索引）
 {
返回dataReader.GetValue（字段索引）如的Int32 ?; 
} 
  

我以前写的关于为与不是快速可空类型如我所料，但这可能是一个稍微不同的情况下...再次，这是值得拥有的一展身手。

不过，我会，如果这真的很奇怪是真正的瓶颈......肯定获得在首位的数据库中的数据将是昂贵得多。你有基准呢？

I have a simple method that returns a Nullable Int32 from a DataReader rather than the built in GetInt32.

I am calling this method many many times and have one situation where any time I can shave off of it would be beneficial.

Can anyone suggest any alternative and faster ways of getting a nullable Int32 out of the DataReader?

private Int32? GetNullableInt32(SqlDataReader dataReader, int fieldIndex)
{
    return !dataReader.IsDBNull(fieldIndex) ? 
                dataReader.GetInt32(fieldIndex) : (Int32?)null;
}

解决方案

I seem to recall that it can sometimes by faster to get the value as an object and then check if that's DBNull.

private Int32? GetNullableInt32(SqlDataReader dataReader, int fieldIndex)
{
    object value = dataReader.GetValue(fieldIndex);
    return value is DBNull ? (Int32?) null : (Int32) value;
}

It's at least worth a try. Note that this is assuming you can unbox straight to an int... I don't know for sure whether that's correct, but it'll be easy to see.

Now there's another approach which is somewhat less safe - it will return null for any non-integer value, even if the field is actually a string, for example:

private Int32? GetNullableInt32(SqlDataReader dataReader, int fieldIndex)
{
    return dataReader.GetValue(fieldIndex) as Int32?;
}

I've previously written about "as" with nullable types not being as fast as I'd expect, but this may be a slightly different case... again, it's worth having a go.

However, I'd be really surprised if this is genuinely a bottleneck... surely getting the data from the database in the first place is going to be far more expensive. Do you have benchmarks for this?

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