索引在FDQuery中不起作用 [英] Indexes don't work in FDQuery

问题描述

我有一个FDQuery，可将数据馈送到网格。

当用户单击列时，我希望网格在该列上排序。
因为我希望能够对多列进行排序，所以不能使用网格的自动排序选项。

I have a FDQuery that feeds data to a grid.
When the user clicks on a column I want the grid to order on that column. Because I want to be able to sort on multiple columns, I cannot use the autosort option of the grid.

我在以下证明中尝试了以下代码：概念。
但是它不起作用。

I tried the following code in my proof of concept. However it does not work.

procedure TForm31.JvDBGrid1TitleBtnClick(Sender: TObject; ACol: Integer;
  Field: TField);
const
  sDesc = 1;
  sASC = 2;
  sNone = 0;
var
  i: integer;
  SortClause: string;
  AField: TField;
  AIndex: TFDIndex;
begin
  case Field.Tag of
    sDesc: Field.Tag:= sASC;
    sASC: Field.Tag:= sNone;
    sNone: Field.Tag:= sDesc;
  end;
  SortClause:= '';
  FDQuery1.Indexes.BeginUpdate;
  try
    FDQuery1.Indexes.Clear;
    for i:= 0 to JvDBGrid1.Columns.Count - 1 do begin
      AField:= JvDBGrid1.Columns[i].Field;
      if AField.Tag <> sNone then begin
        AIndex:= FDQuery1.Indexes.Add;
        AIndex.Name:= AField.FieldName;
        AIndex.Fields:= AField.FieldName;
        //AIndex.Options:= [soNoCase, soNullFirst, soDescNullLast, soDescending, soUnique, soPrimary, soNoSymbols]
        case AField.Tag of
          sDESC: AIndex.Options:= [soDescNullLast];
          sASC: AIndex.Options:= [];
        end;
        AIndex.Active:= true;
      end;
    end;
  finally
    FDQuery1.Indexes.EndUpdate;
    FDQuery1.Refresh;
  end;
end;

查询是否已经有顺序

It does not matter whether the Query already has an order by clause or not.

我在做什么错了？

PS我宁愿不诉诸于构造自定义 order by 子句，但我知道这是一个选择。

P.S. I'd rather not resort to constructing a custom order by clause but I know that's an option.

推荐答案

我认为您可能缺少一个步骤，即将FDQuery的IndexName设置为所添加索引的名称。显然。设置添加的索引的Active属性是不够的。

I think you may be missing a step, namely setting the FDQuery's IndexName to the name of the added index. Apparently. setting the added index's Active property is insufficient.

对于MS Sql Server pubs数据库Authors表，以下对我来说很好用：

The following works fine for me against the MS Sql Server pubs database Authors table:

procedure TForm1.AddFDIndex;
var
  AIndex : TFDIndex;
begin
  AIndex := FDQuery1.Indexes.Add;
  AIndex.Name := 'ByCityThenlname';
  AIndex.Fields := 'city;au_lname';
  AIndex.Active := True;
  FDQuery1.IndexName := AIndex.Name;
end;

顺便说一句，我不确定如果标记了多个列，您的代码应该做什么包含在索引中，但我会留给您; =）

Btw, I'm not sure what your code is supposed to do if more than one column is tagged to be included in the index, but I'll leave that to you ;=)

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