获取数据行到 c# 对象 [英] fetch datarow to c# object

问题描述

我有一个类 Item 表示列表中的一个项目.我有调用返回数据表的存储过程的函数，我需要将数据表转换为项目数组.这是我所做的:

I have an class Item that represents an item in a list. I have in it function that calls stored procedure that returns datatable and I need to convert the datatable to Array of items. Here is what I do:

public class Item
{
    private string _ItemIdDataName = "item_id";
    private string _ItemNameDataName = "item_name";
    private string _PriceDataName = "price";

    public long ItemId { get; set; }
    public string ItemName { get; set; }
    public float Price { get; set; }

    private Item(DataRow row)
    {
        if (row != null)
        {
            ItemId = long.Parse(row[_ItemIdDataName].ToString());
            ItemName = row[_ItemNameDataName].ToString();
            Price = float.Parse(row[_PriceDataName].ToString());
        }
    }

    public Item[] load()
    {
        DataTable dt=DBHandler.GetItems();//Stored procedure that returns DataTable 
        Item[] items = new Item[dt.Rows.Count];
        for (int i = 0; i < dt.Rows.Count; i++)
        {
            items[i] = new Item(dt.Rows[i]);
        }
        return items;
    }
}

我做对了吗?我该如何改进?

Am I doing it right? How can I improve this?

推荐答案

如果你只使用一次它可能没问题，但如果你经常使用它，你应该尝试做一些更通用的东西.我写了一篇关于如何为创建对象列表的 DataTable 编写扩展方法的博客文章.按照约定，对象中的属性应该与存储过程中的列具有相同的名称(如果可以，我会更改存储过程中的名称):

If you're only gonna use it once it probably fine, but if you'll do it a lot you should try to do some more generic stuff. I wrote a blog post about how to write an extension method for DataTable that creates a list of objects. It works by the convention that the properties in the object should have the same name as the columns in the stored procedure (I would change the name in the stored procedure if I could):

public static class DataTableExtensions
{
    public static IList<T> ToList<T>(this DataTable table) where T : new()
    {
        IList<PropertyInfo> properties = typeof(T).GetProperties().ToList();
        IList<T> result = new List<T>();

        foreach (var row in table.Rows)
        {
            var item = CreateItemFromRow<T>((DataRow)row, properties);
            result.Add(item);
        }

        return result;
    }

    public static IList<T> ToList<T>(this DataTable table, Dictionary<string, string> mappings) where T : new()
    {
        IList<PropertyInfo> properties = typeof(T).GetProperties().ToList();
        IList<T> result = new List<T>();

        foreach (var row in table.Rows)
        {
            var item = CreateItemFromRow<T>((DataRow)row, properties, mappings);
            result.Add(item);
        }

        return result;
    }

    private static T CreateItemFromRow<T>(DataRow row, IList<PropertyInfo> properties) where T : new()
    {
        T item = new T();
        foreach (var property in properties)
        {
            property.SetValue(item, row[property.Name], null);
        }
        return item;
    }

    private static T CreateItemFromRow<T>(DataRow row, IList<PropertyInfo> properties, Dictionary<string, string> mappings) where T : new()
    {
        T item = new T();
        foreach (var property in properties)
        {
            if(mappings.ContainsKey(property.Name))
                property.SetValue(item, row[mappings[property.Name]], null);
        }
        return item;
    }
}

现在你可以打电话

var items = dt.ToList<Item>();

或

var mappings = new Dictionary<string,string>();
mappings.Add("ItemId", "item_id");
mappings.Add("ItemName ", "item_name");
mappings.Add("Price ", "price);
var items = dt.ToList<Item>(mappings);

博客文章在这里:http://blog.tomasjansson.com/2010/11/convert-datatable-to-generic-list-extension

有很多方法可以扩展它，你可以包含某种映射字典，告诉扩展如何映射列，这样名称就不需要匹配.或者，您可以添加要在映射中排除的属性名称列表.

There are many ways in which you can extend this, you could include some kind of mapping dictionary telling the extension how to map the columns, in that way the names doesn't need to match. Or you can add a list of property names that you would like to exclude in the mapping.

更新:您正在创建的对象 (Item) 必须具有默认构造函数，否则私有方法将无法创建它.由于解决方案的工作方式是首先创建对象，而不是使用从反射中获得的属性来设置对象的值.

Update: Your object (Item) you are creating must have a default constructor otherwise the private method won't be able to create it. Since the way the solution works is first to create the object than use the properties that you get from the reflection to set the values of the object.

更新 2: 我添加了带有映射字典的部分，但我自己没有尝试过，所以它可能无法编译.然而，这个概念是存在的，我认为它是有效的.

Update 2: I added the part with mappings dictionary but haven't tried it myself so it might not compile. However, the concept is there and I think it works.

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