Question

我正在尝试进行LINQ to Entities查询（我仍然非常熟悉EF并且正在学习它比LinqToSQL差异化）并且我正在尝试做这样的事情：

DateTime begin = new DateTime(2011, 1, 1);

Apps = (from app in context.Instances
                 where app.ReleaseDate.Date == begin
                 select new ScalpApp
                 {
                 Image = app.Image,
                 PublisherName = app.PublisherName,
                 }).ToList();

虽然这在LinqPad中有效，但它不在我的代码中。抛出的异常是：

The specified type member 'Date' is not supported in LINQ to Entities.
只有初始化程序，实体成员和实体导航属性是支撑。

我如何在LinqToEF中执行此操作？ DB中的字段是完整的DateTime（带时间码），我试图仅根据日期进行解析。

Answer 1

你不能简单地使用'app.ReleaseDate.Data'，但你可以：

var begin = new DateTime(2011, 1, 1);
var end = begin.AddHours(24);

Apps = (from app in context.Instances
             where 
               (app.ReleaseDate >= begin) and
               (app.ReleaseDate < end)
             select new ScalpApp
             {
             Image = app.Image,
             PublisherName = app.PublisherName,
             }).ToList();

Answer 2

这个甚至可以在日期字段中使用索引：

DateTime begin = new DateTime(2011, 1, 1);
DateTime end = new DateTime(2011, 1, 2);

Apps = (from app in context.Instances
             where 
               (app.ReleaseDate >= begin) and
               (app.ReleaseDate < end)
             select new ScalpApp
             {
             Image = app.Image,
             PublisherName = app.PublisherName,
             }).ToList();

Answer 3

EF无法将Date DateTime部分转换为SQL代码。但它有EntityFunctions.TruncateTime方法，可以转换为规范的TruncateTime函数：

DateTime begin = new DateTime(2011, 1, 1);

Apps = (from app in context.Instances
        where EntityFunctions.TruncateTime(app.ReleaseDate) == begin
        select new ScalpApp {
            Image = app.Image,
            PublisherName = app.PublisherName,
        }).ToList();

实体框架日期解析

3 个答案: