Question

如何在EF模型中正确处理计算属性？

我的尝试将失败，因为＆＃34;实体或复杂类型＆＃39;发票＆＃39;无法在LINQ to Entities查询中构造。＆＃34;

考虑方法＆＃34; GetInvoice＆＃34;作为带有允许查询字符串的WebApi方法。

static void Main(string[] args)
{
        var invs = GetInvoice();

        invs.FirstOrDefault();

}

public static IQueryable<Invoice> GetInvoice()
{
        var model = new Model();

        IQueryable<Invoice> inv = model.Invocies.Include(t => t.Items).SelectInvoiceData();
        return inv;
}

public static class ExtHelper
{
    public static IQueryable<Invoice> SelectInvoiceData(this IQueryable<Invoice> item)
    {
        return item.Select(c => new Invoice
        {
            LatestItemName = c.Items.FirstOrDefault().Name
        });
    }
}

public class Item
{
    public int Id { get; set; }
    public string Name { get; set; }
    public DateTime CreatedAt { get; set; }
}

public class Invoice
{
    public int Id { get; set; }
    public DateTime CreatedAt { get; set; }

    public string Issuer { get; set; }

    [NotMapped]
    public string LatestItemName { get; set; }

    private ICollection<Item> _items;
    public virtual ICollection<Item> Items
    {
        get { return _items ?? (_items = new Collection<Item>()); }
        set { _items = value; }
    }

}

Answer 1

EntityFramework 6不支持像这样创建部分实体。使用匿名类型：

return item.Select(c => new
{
    LatestItemName = c.Items.FirstOrDefault().Name
});

或某些不属于上下文的DTO类：

return item.Select(c => new InvoiceDTO
{
    LatestItemName = c.Items.FirstOrDefault().Name
});

然而，在EF Core中，可以像您的示例中那样创建实体。

具有实体框架和WebApi的计算属性

1 个答案: