具有连接的数据上下文模型

Question

我想在达成交易时获取有关商家的详细信息。我想翻译这个查询：

select d.*, b.* from deals d inner join business b
on b.id = d.businessId
where d.IsEvent = true

我这样试过：

public List<Deal> GetEventsDeals()
{
    var deals = DataContext.Deals.Join(DataContext.Businesses,
        d => d.BusinessId,
        b => b.Id,
        (d, b) => new {Business = b, Deal = d})
        .Where(d => (d.Deal.IsEvent == true));

    return deals.OrderBy(d => d.Deal.Order).Take(50).ToList();
}

但是我收到一个错误，我需要 return List<AnnoymousType> 并且无法将其转换为 List<Deal>。

如何翻译我的查询？

Answer 1

错误消息告诉您您正在尝试将匿名类型转换为 Deals 类型，但它不知道该怎么做。您需要这样做 代码才能工作

public List<Deal> GetEventsDeals()
{
    var deals = DataContext.Deals.Join(DataContext.Businesses,
        d => d.BusinessId,
        b => b.Id,
        (d, b) => new Deal(){Business = b, Deal = d})
        .Where(d => (d.Deal.IsEvent == true));

    return deals.OrderBy(d => d.Deal.Order).Take(50).ToList();
}

注意：正如 Panagiotis Kanavos 所指出的，这不是 entityframework 设计使用的方式。内部联接应替换为导航属性。

要正确执行此操作，您应该有一个像这样的模型

public class Deal
{
    public int BusinessId { get; set; } 
    [ForeignKey("BusinessId")] // I believe this attribute is redundant because the names follow conventions, but you should check that
    public virtual Business Business { get; set; }
    public bool IsEvent {get;set;}
    public int Order {get;set;}
}

所以你的调用如下

var deals = DataContext.Deals.Include(d => d.Business).Where(d => d.Deal.IsEvent == true);

return deals.OrderBy(d => d.Deal.Order).Take(50).ToList();

具有连接的数据上下文模型

Datacontext models with join

c#

datacontext

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