.NET - 将通用集合转换为数据表 [英] .NET - Convert Generic Collection to DataTable

问题描述

我正在尝试将通用集合(列表)转换为数据表.我找到了以下代码来帮助我做到这一点:

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，当我将 MySimpleClass 的属性之一更改为可空类型时，出现以下错误:

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

DataSet 不支持 System.Nullable<>.

如何使用类中的 Nullable 属性/字段执行此操作?

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

推荐答案

那么大概你需要将它们提升到不可为空的形式，使用 Nullable.GetUnderlyingType，并且可能改变一些null 值到 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...

将分配更改为:

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

并在添加列时:

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

它有效.(?? 是空合并运算符；如果它为非空，则使用第一个操作数，否则计算并使用第二个操作数)

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)

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