Question

我有一份对调查（评估）的回复表，一个地区可以提交多个评估，但我只想要每个区域的最新评估回复。

以下是我的数据，标有*的记录将是我想要返回的记录

      {
"chart": {
    "caption": "Total Profit Calculation",
    "subcaption": "Last month",
    "yAxisname": "Amount (In USD)",
    "numberprefix": "$",
    "connectordashed": "1",
    "sumlabel": "Total {br} Profit",
    "positiveColor": "#6baa01",
    "negativeColor": "#e44a00",
    "paletteColors": "#0075c2,#1aaf5d,#f2c500",
    "baseFontColor": "#333333",
    "baseFont": "Helvetica Neue,Arial",
    "captionFontSize": "14",
    "subcaptionFontSize": "14",
    "subcaptionFontBold": "0",
    "showBorder": "0",
    "bgColor": "#ffffff",
    "showShadow": "0",
    "canvasBgColor": "#ffffff",
    "canvasBorderAlpha": "0",
    "divlineAlpha": "100",
    "divlineColor": "#999999",
    "divlineThickness": "1",
    "divLineDashed": "1",
    "divLineDashLen": "1",
    "usePlotGradientColor": "0",
    "showplotborder": "0",
    "showXAxisLine": "1",
    "xAxisLineThickness": "1",
    "xAxisLineColor": "#999999",
    "showAlternateHGridColor": "0"
},
"data": [
    {
        "label": "Online sales",
        "value": "420000"
    },
    {
        "label": "Store Sales",
        "value": "710000"
    },
    {
        "label": "Total Sales",
        "issum": "1"
    },
    {
        "label": "Fixed Costs",
        "value": "-250000"
    },
    {
        "label": "Variable Costs",
        "value": "-156000"
    },
    {
        "label": "COGS",
        "value": "-310000"
    },
    {
        "label": "Promotion Costs",
        "value": "-86000"
    },
    {
        "label": "Total Costs",
        "issum": "1",
        "cumulative": "0"
    }
]
  }

到目前为止，这是我的linq，但它只返回2个回复

AsessmentID AssessmentDate Status  AreaID Response Category
          1    01/01/2016  Complete    1       1    A
          1    01/01/2016  Complete    1       2    B
          1    01/01/2016  Complete    1       4    C
          2    05/01/2016  Complete    1       5*   A
          2    05/01/2016  Complete    1       4*   B
          2    05/01/2016  Complete    1       5*   C
          3    02/01/2016  Complete    2       1*   A
          3    02/01/2016  Complete    2       2*   B
          3    02/01/2016  Complete    2       4*   C
          4    03/01/2016  Complete    3       5*   A
          4    03/01/2016  Complete    3       4*   B
          4    03/01/2016  Complete    3       5*   C
          5    04/01/2016  Draft       3       3    A
          5    04/01/2016  Draft       3       2    B
          5    04/01/2016  Draft       3       3    C

Answer 1

你可以这样做：

var results = db.Answers
    .Where(x => x.Status == Status.Complete)
    .GroupBy(x => x.AreaID)     //group by AreaID
    .Select(x => new            //project onto anonymous type with the data we need
    {
        //the AreaID
        AreaID = x.Key,         

        //get a collection for the responses we need
        Responses = x           
            //Group by the date of the assessment
            .GroupBy(r => r.AssessmentDate)

            //order descending so we get the last responses
            .OrderByDescending(r => r.Key)

            //take only the first in the list (latest)
            .Take(1)

            //project the ordered result extracting the properties we want to show
            .SelectMany(r => r.Select(ri => new { ri.AssessmentDate, ri.Response}))
    })
    //enumerate 
    .ToList();

使用此代码打印到控制台：

foreach (var g in results)
{
    Console.WriteLine("AreaID: {0}", g.AreaID);
    Console.WriteLine("Date      Response");
    foreach (var r in g.Responses)
        Console.WriteLine("{0} {1}", r.AssessmentDate.ToShortDateString().PadRight(10,' '), r.Response);

    Console.WriteLine();
}

你应该得到这个：

AreaID: 1
Date      Response
5/1/2016   5
5/1/2016   4
5/1/2016   5

AreaID: 2
Date      Response
2/1/2016   1
2/1/2016   2
2/1/2016   4

AreaID: 3
Date      Response
3/1/2016   5
3/1/2016   4
3/1/2016   5

希望这有帮助！

组合几个字段并选择最新日期？

1 个答案: