如何在lambda表达式或linq中执行此操作? [英] How to do this in lambda expression or linq?

问题描述

我有这个要求，

一个产品可以有多个图像，并且只能包含一个默认图像.如果属性isDefault等于true，则可以确定产品的默认图像.

A product can have multiple images and only one default image. You can determine the default image of the product if the property isDefault is equal to true.

我想用LINQ和lambda来做，但是我被卡在代码里:

I want to do it in LINQ and lambda but I'm stucked in my code:

private class ProdcutImages
{
    public Int32 ID { get; set; }
    public String ProductID { get; set; }
    public Boolean IsDefault { get; set; }
    public Image Image { get; set; }
    public String FileName { get; set; }
}

public void SetDefaultImage(int productID)
{
    SqlConnection conn = getConnection();
    conn.Open();
    SqlDataAdapter da = new SqlDataAdapter("SELECT * FROM product_images WHERE product_id = @ID", conn);
    da.SelectCommand.Parameters.Add(new SqlParameter("@ID", productID));


    DataTable dt = new DataTable();
    da.Fill(dt);

    var imageList = (from tr in dt.AsEnumerable()
                        select new ProdcutImages()
                        {
                            ID = tr.Field<int>("id"),
                            ProductID = tr.Field<string>("productId"),
                            IsDefault = tr.Field<bool>("isDefault"),
                            Image = tr.Field<Image>("image"),
                            FileName = tr.Field<string>("fileName")
                        }).ToList();

    pictureBox1.Image = // ???
    conn.Close();
}

推荐答案

可能是这样:

var img = imageList.FirstOrDefault(i => i.IsDefault);
if (img != null) { pictureBox1.Image = img.Image; }

或者，考虑到有人忘记在任何图像上设置IsDefault字段的情况:

or, to take into account the case someone forgot to set the IsDefault field on any image:

var img = imageList.FirstOrDefault(i => i.IsDefault) ?? imageList.FirstOrDefault();
if (img != null) { pictureBox1.Image = img.Image; }

(如果未将其设置为默认值，它将使用第一个可用图像)

(this would use the first available image if none is set as default)

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