This is a multi-table connection and how to return null values to foreign key fields in the ASPNET.
The background of the database is like this:
Equipment Table A, Foreign Committe: Supply_ID (Supplier Serial Number) Data Type: INT, Allowed
Supplier table B, primary key: Suppirl_id (vendor number) Data type: int, as a seed
1. Since it is not a vendor record, there is a number of record_ids with a plurality of records in A.
2. Since the Support_ID in B is an identification seed starting from 1, in order to correspond to the corresponding relationship, the content of the data is maintained, the content of the a.Supply_ID is an integer equal to 1.
I used A to the left-way connection to B.
This is the result I discussed in the morning, and it seems to have passed the test data. But in the afternoon, I used ASPNET to access the device table, and there was a problem with it.
I use the DropDownList control to bind the supplier,
/ * Binding supplier DPDOWNLIST * /
String sup_sql = "SELECT Supply_ID, Supply_Name from Supply";
mysql.runload (SUP_SQL); // MySQL is a public class, a collection of database connections and access
DropDownList2.Items.add (New ListItem ("," 0 "))); // The first item of the drop-down menu is empty, in order to show the devices that have no supplier. TEXT is empty, Value is O
While (mysql.myDataReader.Read ())
DropdownList2.items.add (NEW ListItem (MySQL.MYDATAREADER [1] .tostring (), mysql.mydatareader [0] .tostring ()))); // The binding of the supplier is just the serial number (Supply_ID) And supplier name (Supply_Name) a SelectIndex, and a value value, a text value.
Then I connect to the database and start accessing the data, no problem.
IF (MySql.myDataReader [Suppy_ID] == "")
DropDownList1.selectIndIndex = 0;
Else
{
DropdownList1.selectIndIndex = Convert.Toint (mysql.mydatareader [suppy_id] .tostring ())
}
The problem is in the modification of the data and returns back to the database!
I modified the vendor to replace the value of DropDownList1.selectIndex, so the repossed SQL statement is
Update machine set supply_id = dropdownloadList1.selectIndex
When I selected null, (no supplier), DropDownList1.selectIndex = 0,0 was returned to the original A.Supply_ID, when we stipulated that the content of this field started from 1, this The contradiction between the number of times during reading data is caused.
Solution:
Changed all the foreign keys in the database to 0, the DropDownList binds the supplend table, it has already been vacated with SlectIndex = 0, Value = 0, has nothing to do, but when the database is accessed, Put
IF (MySql.myDataReader [Suppy_ID] == "") DropDownList1.selectIndIndex = 0;
Else
{
DropdownList1.selectIndIndex = Convert.Toint (mysql.mydatareader [suppy_id] .tostring ())
}
This big section is changed
DropDownList1.selectIndex = Convert.TOINT (MySql.myDataReader [Suppy_ID] .tostring ());
The previous external connection does not change, and the data consistency and integrity can be solved.
