Question

我有一个SQL表，正在使用Entity Framework Core。在将记录从Excel文件上传到此表的过程中，我还添加了一个简单的datetime的“上传日期”（DateTime.Today）列。

例如：

record | id | employee | customer| project | hours | uploadDate |

现在，我想要一个仅显示记录最新上传的视图。你知道一个好的lambda / LINQ吗？

_context.TableWithRecords.Where(DateTime.Max?).ToList();

基本上或类似的东西。

Answer 1

听起来您想要这样的东西：

@Override
public void start(Stage primaryStage) {
    VBox content = new VBox();
    ScrollPane scrollPane = new ScrollPane(content);
    VBox.setVgrow(scrollPane, Priority.ALWAYS);
    Button button = new Button("fill");
    button.setOnAction(evt -> {
        for (int i = 0; i < 20; i++) {
            content.getChildren().add(new Text(Integer.toString(i)));
        }
        System.out.println("content size before layout: " + content.getHeight());

        // manually layout scrollPane
        scrollPane.applyCss();
        scrollPane.layout();

        System.out.println("content size after layout: " + content.getHeight());
        scrollPane.setVvalue(1d);
    });

    Scene scene = new Scene(new VBox(button, scrollPane), 200, 200);
    primaryStage.setScene(scene);
    primaryStage.show();
}

这将按上传日期进行分组，然后按降序排列以使最近上传的组成为第一组，然后抓取第一组并返回所有这些结果。

使用以下示例数据进行测试：

_context
    .TableWithRecords
    .GroupBy(x => x.uploadDate)
    .OrderByDescending(x => x.Key)
    .First()
    .ToList();

其中var dates = new List<TestRecord> { new TestRecord { Record = "1", Date = new DateTime(2018, 8, 1) }, new TestRecord { Record = "2", Date = new DateTime(2018, 8, 1) }, new TestRecord { Record = "3", Date = new DateTime(2018, 8, 1) }, new TestRecord { Record = "4", Date = new DateTime(2018, 8, 2) }, new TestRecord { Record = "5", Date = new DateTime(2018, 8, 2) }, new TestRecord { Record = "6", Date = new DateTime(2018, 8, 2) }, };定义为：

TestRecord

给出期望的输出：

public class TestRecord
{
    public string Record { get; set; }
    public DateTime Date { get; set; }
}

Answer 2

我将使用两个查询：

DateTime? maxDate = _context.TableWithRecords.Max(x => x.uploadedDate);
var result = _context.TableWithRecords.Where(x => x.uploadDate == maxDate).ToList()

获取最新上传的记录

2 个答案: