如何根据 1 个组合框中的选择过滤 2 个组合框？

Question

我有 3 张桌子：

1) 房子：

| ID_house | House_names | num_region |
---------------------------------------
|   int    |    names    |    int     |

num_region - 外键，相当于Region表中的主键(Region.ID_region)。

2) 地区：

| ID_region | Nameofregions | num_arearegion |
---------------------------------------------
|   int     |    names      |      int       |

num_arearegion - 外键，等于 Areas_InRegion 表中的主键(Areas_InRegion.ID_areas)。

3) Areas_InRegion：

| ID_areas | Area_names |
------------------------
|   int   |    names   |

在表单中我有 3 个组合框：

1) cmbHouse - 用于显示 House 表中的房屋名称。

2) cmbRegion - 用于显示 Region 表中的区域名称。

3) cmbArea - 用于显示 Areas_InRegion 表中区域中的区域名称。

我这样填充组合框：

    //cmbHouse
    string cmbHouse_query = "SELECT * FROM House";
    OleDbDataAdapter dahouse = new OleDbDataAdapter(cmbHouse_query, connection);
    DataTable tablehouse = new DataTable();
    dahouse.Fill(tablehouse);
    cmbHouse.DataSource = tablehouse;
    cmbHouse.DisplayMember = "House_names"; 
    cmbHouse.ValueMember = "House.num_region";
    cmbHouse.SelectedIndex = -1;

    //cmbRegion
    string cmbRegion_query = "SELECT * FROM Region";
    OleDbDataAdapter daregion = new OleDbDataAdapter(cmbRegion_query, connection);
    DataTable tableregion = new DataTable();
    daregion.Fill(tableregion);
    cmbRegion.DataSource = tableregion;
    cmbRegion.DisplayMember = "Nameofregions";
    cmbRegion.ValueMember = "Region.ID_region";
    cmbRegion.SelectedIndex = -1;

    //cmbArea
    string cmbArea_query = "SELECT * FROM Areas_InRegion";
    OleDbDataAdapter daArea = new OleDbDataAdapter(cmbArea_query, connection);
    DataTable tablearea = new DataTable();
    daArea.Fill(tablearea);
    cmbArea.DataSource = tablearea;
    cmbArea.DisplayMember = "Names_OfAreas";
    cmbArea.ValueMember = "Areas_InRegion.ID_areas";
    cmbArea.SelectedIndex = -1;

Combobox cmbRegion 有 valuemember 作为主键。

我可以通过主键过滤 cmbHouse 组合框作为 cmbRegion 组合中的 valuemeber，但我不能过滤 cmbArea 组合框。

    private void cmbHouse_SelectionChangeCommitted(object sender, EventArgs e)
    {
        if (cmbHouse.SelectedIndex > -1)
        {
            //DataRow selectedDataRow = ((DataRowView)cmbHouse.SelectedItem).Row;
            int num_region = Convert.ToInt32(cmbHouse.SelectedValue);

            OleDbCommand com = new OleDbCommand();
            com.CommandText = "SELECT * FROM Region WHERE Region.ID_region=" + num_region.ToString() + "";
            //com.Parameters.AddWithValue("House.num_region", typeof(int));
            OleDbDataAdapter danum_region = new OleDbDataAdapter(com.CommandText, connection);
            DataTable tablenum_region = new DataTable();
            danum_region.Fill(tablenum_region);
            cmbRegion.DataSource = tablenum_region;
            cmbRegion.DisplayMember = "Nameofregions";
            cmbRegion.ValueMember = "Region.num_arearegion";
            //cmbRegion.SelectedIndex = -1;
            if(cmbRegion.SelectedIndex > -1)
            {
                int num_area = Convert.ToInt32(cmbRegion.SelectedValue);

                OleDbCommand com2 = new OleDbCommand();

                com2.CommandText = "SELECT * FROM Areas_InRegion WHERE Areas_InRegion.ID_areas=" + num_area.ToString(); // + num_area.ToString() + " ; WHERE Region.num_arearegion=@Areas_InRegion.ID_area
                                                                                                                        //com2.Parameters.AddWithValue("@Areas_InRegion.ID_area", num_area);
                OleDbDataAdapter danum_area = new OleDbDataAdapter(com2.CommandText, connection);
                DataTable tablenum_area = new DataTable();
                //tablenum_area.DefaultView.RowFilter = "Areas_InRegion.ID_areas=" + num_area.ToString();
                danum_area.Fill(tablenum_area);

                cmbArea.DataSource = tablenum_area;
                cmbArea.DisplayMember = "Names_OfAreas";
                cmbArea.ValueMember = "Areas_InRegion.ID_areas";
                //cmbArea.SelectedIndex = -1;
            }
        }                
    }

为此，必须有另一个 valuemeber 作为外键 [Region.num_areas]。

是否可以在每个组合框中有多个值成员？

当我点击任何组合框时，其他组合框应该被过滤掉。

请帮帮我。

谢谢。

Answer 1

一栋房子位于一个区域（1-1 关系），一个区域可以有一个或多个区域（1-n 关系），一个区域属于一个且仅一个区域关系您的数据库架构错误。你需要这样的东西（因为显然一所房子只能位于一个区域）

1) House:
| ID_house | House_names | ID_region | ID_areas |
--------------------------------------------------
|   int    |    names    |    int     | int      |

2) Region:
| ID_region | Nameofregions |
-----------------------------
|   int     |    names      |

3) Areas:
| ID_areas | Area_names | ID_region |
-------------------------------------
|   int   |    names    | int       |

现在，当您获得房屋的 id 时，您还获得了地区和区域的 id。

private void cmbHouse_SelectionChangeCommitted(object sender, EventArgs e)
{
    if (cmbHouse.SelectedIndex > -1)
    {
        // Each item in a combobox binded to a datatable is a DataRowView
        // If we get this object we can access all the columns from that row
        DataRowView rv = cmbHouse.SelectedItem as DataRowView;

        // Extract the fk for the region and the area
        int id_region = Convert.ToInt32(rv["ID_region"]);
        int id_area = Convert.ToInt32(rv["ID_area"]);

        // at startup you have already filled the combo with the regions,
        // so there is no need to look again in the database for the region
        // Just set the current selected value to the region
        cmbRegion.SelectedValue = num_region;

        // the same happens for the Areas combo. It is already filled with the 
        // areas, but here we should really have only the areas that belongs to 
        // the selected region not all the area to avoid problems 
        // (so remove the initial filling and do it only when the user choose an House)
        // Query for all areas belonging to the selected region
        string areaSql = @"SELECT * FROM Areas 
                           WHERE ID_Region=@reg";
        OleDbCommand com2 = new OleDbCommand(areaSql, connection);
        com2.Parameters.AddWithValue("@reg", num_region);
        OleDbDataAdapter danum_area = new OleDbDataAdapter(com2);
        DataTable tablenum_area = new DataTable();
        danum_area.Fill(tablenum_area);

        // Always put the Datasource after the setting for DisplayMember and ValueMember 
        // to avoid performance drops and problems if there is a SelectedIndexChanged event
        cmbArea.DisplayMember = "Names_OfAreas";
        cmbArea.ValueMember = "ID_areas";
        cmbArea.DataSource = tablenum_area;

        // last step is setting the SelectedValue on the cmbArea to the house's area 
        cmbArea.SelectedValue = id_area;
    }
}