具有不同函数的 linq 问题

发布于 2024-11-08 06:26:45 字数 778 浏览 0 评论 0原文

我正在尝试将不同的记录绑定到下拉列表。在我添加 linq 查询的不同函数后，它说“DataBinding：'System.String'不包含名称为'Source'的属性。”我可以保证该列名称是'Source'。进行不同搜索时该名称是否会丢失？

我的后端代码：

public IQueryable<string> GetAllSource()
        {
            PromotionDataContext dc = new PromotionDataContext(_connString);
            var query = (from p in dc.Promotions
                         select p.Source).Distinct();
            return query;
        }

前端代码：

PromotionDAL dal = new PromotionDAL();
        ddl_Source.DataSource = dal.GetAllSource();
        ddl_Source.DataTextField = "Source";
        ddl_Source.DataValueField = "Source";
        ddl_Source.DataBind();

有人有解决方案吗？先感谢您。

原文

I am trying to bind distinct records to a dropdownlist. After I added distinct function of the linq query, it said "DataBinding: 'System.String' does not contain a property with the name 'Source'. " I can guarantee that that column name is 'Source'. Is that name lost when doing distinct search?

My backend code:

public IQueryable<string> GetAllSource()
        {
            PromotionDataContext dc = new PromotionDataContext(_connString);
            var query = (from p in dc.Promotions
                         select p.Source).Distinct();
            return query;
        }

Frontend code:

PromotionDAL dal = new PromotionDAL();
        ddl_Source.DataSource = dal.GetAllSource();
        ddl_Source.DataTextField = "Source";
        ddl_Source.DataValueField = "Source";
        ddl_Source.DataBind();

Any one has a solution? Thank you in advance.

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昵称有卵用 2024-11-15 06:26:45

您已经在 LINQ 查询中选择了 Source，这就是结果是 IQueryable 的方式。然后，您还将Source指定为要在数据绑定中的每个字符串中查找的属性。只需取出更改数据绑定中的 DataTextField 和 DataValueField 属性的语句即可。

或者，您可以从查询中删除对 p.Source 的投影并返回 IQueryable - 但随后您会得到不同的促销比不同的来源。

另一项快速说明 - 使用查询语法并不能真正帮助您进行 GetAllSources 查询。我只是将其写为：

public IQueryable<string> GetAllSource()
{
    PromotionDataContext dc = new PromotionDataContext(_connString);
    return dc.Promotions
             .Select(p => p.Source)
             .Distinct();
}

查询表达式非常适合复杂的查询，但是当您只有一个 select 或一个 where 子句和一个简单的投影时，在我看来，使用点表示法更简单。

You're already selecting Source in the LINQ query, which is how the result is an IQueryable<string>. You're then also specifying Source as the property to find in each string in the databinding. Just take out the statements changing the DataTextField and DataValueField properties in databinding.

Alterantively you could remove the projection to p.Source from your query and return an IQueryable<Promotion> - but then you would get distinct promotions rather than distinct sources.

One other quick note - using query syntax isn't really helping you in your GetAllSources query. I'd just write this as:

public IQueryable<string> GetAllSource()
{
    PromotionDataContext dc = new PromotionDataContext(_connString);
    return dc.Promotions
             .Select(p => p.Source)
             .Distinct();
}

Query expressions are great for complicated queries, but when you've just got a single select or a where clause and a trivial projection, using the dot notation is simpler IMO.

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