Question

So I have thousands of objects, of generic type T, and I want to cast them to an array of objects I got. So I have to get the properties list T, and for each property set the value to the corresponding object on the array

for (int i = 0; reader.Read(); i++)
{
    T tmp = (T)Activator.CreateInstance(typeof(T));
    foreach (var prop in properties)
    {         
        prop.SetValue(tmp, reader.GetValue(reader.GetOrdinal(prop.Name)), null);
    }
}

reader is a DataReader. The problem I have is that prop.SetValue is sadly slow (consumes like 50% of the total excecution time), I ve been told to use Dynamic Methods or Expression Trees, I tried using expression trees but from what I understood I have to generate one tree for each value I want to set, which wouldn t be so good. So Dynamic Methods is the other option. Ideally I d need to create a method SetProp(object, propertyName, value) which I can reuse over and over again.

Answer 1

查阅;要么使用“as is”,要么偷窃所有代码(DynamicMethod)。它做了这一切,并建立了反省等。例常使用:

var accessor = TypeAccessor.Create(typeof(T)); 
for (int i = 0; reader.Read(); i++)
{
    T tmp = (T)Activator.CreateInstance(typeof(T));
    foreach (var prop in properties)
    {         
        accessor[tmp, propName] = newValue; // fill in name/value here
    }
}

或者说,使用诸如dapper-dot-net等内容,即和处理所有材料化(因为这显然是数据检索代码)。

Answer 2

我尝试使用表达的树木,但从我的理解中,我不得不为我所想确定的每一价值生产一 tree树,而这种树本不会很好。

为什么不呢? 您基本上建立了<代码>List<Tuple<string, Action<object>>>,在中为每个财产创建(然后编纂)表达树。 T。然后,你就每个财产的清单和项目进行核对,然后称为相应的行动。

页: 1 MiscUtil的班级非常相似,你可能希望从中学习。

或者,截至网络4,你可以建造一个单独的<代码>Block表述树,该树确实在all上登记。

Answer 3

You can create a single expression tree for each property.
Just take the value as a parameter:

var instance = Expression.Parameter(typeof(T));
var value = Expression.Parameter(typeof(object));
var setter = Expression.Lambda(
    Expression.SetProperty(instance, Expression.Cast(value, prop.PropertyType)),
    instance, value
);

您将每例一次创建和编辑这些表达的树木(通常见)。普通类:。

在你回头的时候,你也许可以通过汇编另一个表达树而不是<条码>活着者.CreateInstance(<>来更快地做到这一点。

友情链接