Question

我有一个Linq查询，我将传递给一个列表，然后通过viewbag传递给视图。我试图按照特定的顺序保留该列表，这样当我遍历它时，我可以控制它显示的顺序。

以下是查询：

    from flask import Flask, render_template, redirect, request
from xml_identifiersearch import searchXML, printHTML
from xml_time import sortDate, returnDateFile, dateRange, searchXML, printDateHTML

app = Flask(__name__)

@app.route('/') 
def index():
    return render_template('home.html')       

@app.route('/',methods=['POST'])
def run():
    printHTML(request.form['input'])
    return render_template('home.html')

@app.route('/',methods=['POST'])
def run2():
    startYear=request.form['startYear']
    startMonth=request.form['startMonth']
    startDay=request.form['startDay']
    startHour=request.form['startHour']
    startMinute=request.form['startMinute']
    startSecond=request.form['startSecond']
    startMillisecond=request.form['startMillisecond']
    endYear=request.form['endYear']
    endMonth=request.form['endMonth']
    endDay=request.form['endDay']
    endHour=request.form['endHour']
    endMinute=request.form['endMinute']
    endSecond=request.form['endSecond']
    endMillisecond=request.form['endMillisecond']
    startDatetime=startYear+"-"+startMonth+"-"+startDay+"T"+startHour+":"+startMinute+":"+startSecond+"."+startMillisecond+"Z"
    endDatetime=endYear+"-"+endMonth+"-"+endDay+"T"+endHour+":"+endMinute+":"+endSecond+"."+endMillisecond+"Z"
    printDateHTML(startDatetime, endDatetime)
    return render_template('home.html')

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=5000,debug=True)

我成功地将此列表传递给视图并迭代它，但无论值始终按字母顺序显示。 ViewBag.attributes = (From row In db.tblCategory_Attributes Where row.Item_Type_Identifier = itemType Order By row.Category_Attribute_Identifier Select CStr(row.Attribute_Name) Distinct).ToList()是一个整数，与我希望显示这些值的顺序一致。

我已经玩了很多我的陈述的顺序，我没有运气。

您能告诉我如何明确选择与我的特定Category_Attribute_Identifier相关的Attribute_Name并按Item_Type_Identifier订购我的结果吗？

Answer 1

Distinct再次创建自己的排序（因为它会对结果进行混洗以过滤掉重复项）。只需在Distinct：

之后进行排序

(From row In db.tblCategory_Attributes
 Where row.Item_Type_Identifier = itemType
 Select row
 Distinct)
 .OrderBy(Function(row) row.Category_Attribute_Identifier)
 .Select(Function(row) CStr(row.Attribute_Name))

Answer 2

尝试使用Group By代替Distinct

ViewBag.attributes = (From row In db.tblCategory_Attributes _
                      Where row.Item_Type_Identifier = itemType _
                      Order By row.Category_Attribute_Identifier) _
                    .AsEnumerable() _
                    .GroupBy(Function(r) r.Attribute_Name) _
                    .Select(Function(g) g.Key) _
                    .ToList()

或者使用扩展方法语法，它允许您以任何顺序自由地应用扩展方法：

ViewBag.attributes = db.tblCategory_Attributes _
    .Where(Function(row) row.Item_Type_Identifier = itemType) _
    .Select(Function(row) New With {row.Attribute_Name, row.Category_Attribute_Identifier}) _
    .Distinct() _
    .OrderBy(Function(a) a.Category_Attribute_Identifier) _
    .Select(Function(a) a.Attribute_Name) _
    .ToList()

这个简单的测试表明GroupBy保留了顺序：

Public Shared Sub TestGroupOrder()
    Dim a = New Integer() {6, 2, 4, 2, 7, 5, 3, 4}
    Dim query = a.GroupBy(Function(i) i).[Select](Function(g) g.Key)
    For Each i As Integer In query
        Console.Write("{0} ", i)
    Next
End Sub

控制台中的结果：

6 2 4 7 5 3

linq使用order by，where和select vb.net

2 个答案: