LINQ to Entities 无法识别方法 'System.String Format(System.String, System.Object, System.Object)'

Question

我有这个 linq 查询:

private void GetReceivedInvoiceTasks(User user, List<Task> tasks)
{
    var areaIds = user.Areas.Select(x => x.AreaId).ToArray();

    var taskList = from i in _db.Invoices
                   join a in _db.Areas on i.AreaId equals a.AreaId
                   where i.Status == InvoiceStatuses.Received && areaIds.Contains(a.AreaId)
                   select new Task {
                       LinkText = string.Format(Invoice {0} has been received from {1}, i.InvoiceNumber, i.Organisation.Name),
                       Link = Views.Edit
                   };
}

但它有问题。我正在尝试创建任务。对于每个新任务，当我将链接文本设置为像“Hello”这样的常量字符串时，就可以了。但是，上面我尝试使用发票的属性构建属性链接文本。

我收到此错误:

base {System.SystemException} = {"LINQ to Entities does not recognize the method 'System.String Format(System.String, System.Object, System.Object)' method, and this method cannot be translated into a store expression."}

有人知道为什么吗？有人知道另一种方法可以使其发挥作用吗？

Answer 1

Entity Framework 正在尝试在 SQL 端执行您的投影，其中没有与 string.Format 等效的项。 。使用AsEnumerable()强制使用 Linq to Objects 评估该部分。

基于on the previous answer我已经给过你，我会像这样重组你的查询:

int statusReceived = (int)InvoiceStatuses.Received;
var areaIds = user.Areas.Select(x=> x.AreaId).ToArray();

var taskList = (from i in _db.Invoices
               where i.Status == statusReceived && areaIds.Contains(i.AreaId)
               select i)
               .AsEnumerable()
               .Select( x => new Task()
               {
                  LinkText = string.Format("Invoice {0} has been received from {1}", x.InvoiceNumber, x.Organisation.Name),
                  Link = Views.Edit
                });

此外，我发现您在查询 (Organization.Name) 中使用了相关实体，请确保将正确的 Include 添加到查询中，或者专门具体化这些属性以供以后使用使用，即:

var taskList = (from i in _db.Invoices
               where i.Status == statusReceived && areaIds.Contains(i.AreaId)
               select new { i.InvoiceNumber, OrganisationName = i.Organisation.Name})
               .AsEnumerable()
               .Select( x => new Task()
               {
                  LinkText = string.Format("Invoice {0} has been received from {1}", x.InvoiceNumber, x.OrganisationName),
                  Link = Views.Edit
                });