如何在Lambda LINQ中排除属性而不是选择 [英] How to Except Property instead of Select in Lambda LINQ

问题描述

我有一个获取表的代码。这是我的示例代码：

I have a code that fetching a table. Here's my sample code:

public IQueryable<MyItem> MyItems(){
    return context.MyItem;
}

以下是MyItem的示例属性

Here are the sample properties of MyItem

public int Id {get;set;}
public byte[] Image {get;set;}
public string Name {get;set;}

因为， byte [] 可以有多个字符，我不想在搜索中包括，因为如果我有10,000个项目之类的记录将花费很长时间。

Since, byte[] can have multiple characters, I don't want to include then in searching because it will take so long if I have a records like 10,000 items.

通常，我会选择，例如：

public IQueryable<MyItem> MyItems(){
    return context.MyItem.Select(item=>new MyItem{
        Id=item.Id,
        Name=item.Name
    });
}

这对少数酒店而言还可以，但我拥有10到20处酒店，将它们一一写入很麻烦。

This is okay for few properties, but what I have a 10-20 properties, it would be hassle to write them one by one.

有什么办法，只是我的lambda中的 Image 属性用于更短的代码？

Is there any way like, I just Except the property Image in lambda for shorter code?

推荐答案

创建自己的扩展方法 SelectExcept ：

public static IQueryable<T> SelectExcept<T, TKey>(this IQueryable<T> sequence,
    Expression<Func<T, TKey>> excluder)
{
    List<string> excludedProperties = new List<string>();
    if (excluder.Body is MemberExpression memberExpression)
    {
        excludedProperties.Add(memberExpression.Member.Name);
    }
    else if (excluder.Body is NewExpression anonymousExpression)
    {
        excludedProperties.AddRange(anonymousExpression.Members.Select(m => m.Name));
    }
    var includedProperties = typeof(T).GetProperties()
        .Where(p => !excludedProperties.Contains(p.Name));

    return sequence.Select(x => Selector(x, includedProperties));
}

private static T Selector<T>(T obj, IEnumerable<PropertyInfo> properties)
{
    var instance = Activator.CreateInstance<T>();
    foreach (var property in properties)
        property.SetValue(instance, property.GetValue(obj), null);

    return instance;
}

在客户端中：

var result = context.MyItem.SelectExcept(x => x.Image);

您可以排除多个物业：

var result = context.MyItem.SelectExcept(x => new { x.Image, x.Name });

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