我有3张桌子：
1）房子：
| ID_house | House_names | num_region |
---------------------------------------
| int | names | int |
num_region-外键，它等于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 |
我有3个组合框：
1）cmbHouse-用于显示“房屋”表中房屋的名称。
2）cmbRegion-用于显示“区域”表中区域的名称。
3）cmbArea-用于显示Areas_InRegion表中区域的区域名称。
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;
组合框cmbRegion具有valuemember作为主键。
我可以通过主键筛选cmbHouse组合框作为cmbRegion组合中的valuemeber，但是我不能筛选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，有必要另一个值成员作为外键[Region.num_areas]。
在每个组合框中是否可以有多个valuemember？
当我单击任意组合框时，其他组合框应被过滤。
请帮助我。
谢谢。
答案 0 :(得分：0)
房屋位于一个区域（1-1关系）中，一个区域可以具有一个或多个区域（1-n关系），一个区域属于一个并且只有一个区域关系，您的数据库架构错误。您需要像这样的东西（因为显然一所房子只能位于一个区域中）
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，您还将获得区域和区域的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;
}
}