.NET - 转换泛型集合到数据表 [英] .NET - Convert Generic Collection to DataTable

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问题描述

我想泛型集合(列表)转换为数据表。我发现下面的code帮我做到这一点:

I am trying to convert a generic collection (List) to a DataTable. I found the following code to help me do this:

// Sorry about indentation
public class CollectionHelper
{
private CollectionHelper()
{
}

// this is the method I have been using
public static DataTable ConvertTo<T>(IList<T> list)
{
    DataTable table = CreateTable<T>();
    Type entityType = typeof(T);
    PropertyDescriptorCollection properties = TypeDescriptor.GetProperties(entityType);

    foreach (T item in list)
    {
        DataRow row = table.NewRow();

        foreach (PropertyDescriptor prop in properties)
        {
            row[prop.Name] = prop.GetValue(item);
        }

        table.Rows.Add(row);
    }

    return table;
}    

public static DataTable CreateTable<T>()
{
    Type entityType = typeof(T);
    DataTable table = new DataTable(entityType.Name);
    PropertyDescriptorCollection properties = TypeDescriptor.GetProperties(entityType);

    foreach (PropertyDescriptor prop in properties)
    {
        // HERE IS WHERE THE ERROR IS THROWN FOR NULLABLE TYPES
        table.Columns.Add(prop.Name, prop.PropertyType);
    }

    return table;
}
}

我的问题是,当我改变MySimpleClass的特性之一,可空类型,我得到以下错误:

My problem is that when I change one of the properties of MySimpleClass to a nullable type, I get the following error:

的DataSet不支持System.Nullable&LT;方式&gt;

我如何在我的课这样做可空的属性/字段?

How can I do this with Nullable properties/fields in my class?

推荐答案

然后presumably你需要将它们提升到非空形式,使用 Nullable.GetUnderlyingType ,也许改变一些 DbNull.Value ...

Then presumably you'll need to lift them to the non-nullable form, using Nullable.GetUnderlyingType, and perhaps change a few null values to DbNull.Value...

更改任务是:

row[prop.Name] = prop.GetValue(item) ?? DBNull.Value;

和添加列时是:

table.Columns.Add(prop.Name, Nullable.GetUnderlyingType(
            prop.PropertyType) ?? prop.PropertyType);

和它的作品。 ( ?? 是空合并运算符;它使用第一个操作数,如果它是非空,否则第二个操作数的计算和使用)

And it works. (?? is the null-coalescing operator; it uses the first operand if it is non-null, else the second operand is evaluated and used)

这篇关于.NET - 转换泛型集合到数据表的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!

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