Explanation of the Code

Through BASIC+ calls, OpenInsight communicates with the Access database through use of objects. Two objects are used:

The Connection object, which manages the connection between OpenInsight and Access. The functions that use the Connection object have the prefix XO (XOGetProperty(), XOInstance(), XOMethod(), and XOSetProperty()). BASIC+ communicates with the Northwind database through the NWIND connection, defined previously in the Client/Server workspace.
The Query object, which sends the query to Access using the Connection object and receives the results. The functions that use the Query object have the prefix Qry (QryGetProperty(), QryInstance(), QryMethod(), and QrySetProperty()). Once the NWIND connection object has been established ("instantiated" is the fancy object-oriented term), the Query object can be used to run database queries using that connection.

The XO_Equates $Insert record contains declarations and equates for arguments and functions that are used with the Connection object and the Query object.

The logic flow is as follows:

Create ("instantiate") a Connection object. To instantiate the object, call XOInstance(), passing the connection name. If successful, the connection "handle", a nonzero number, is returned in hXO. Calling XOInstance() is the equivalent, in code, of the NWIND connection object we created in the Client/Server workspace. The code is as follows:
```
hXO = XOInstance('NWIND')
```
Instantiate a Query object. After we have a handle to the Connection object, we can use it to create a Query object. This is done using QryInstance(). If successful, the query handle will be a nonzero number, returned in hQry. The code is as follows:
```
hQry = QryInstance(hXO)
```
Execute the Query. The query handle can be used to execute the query. To execute a "method" (function), use QryMethod(). The QRY_EXECUTE$ code (equated to 4 in XO_Equates) is used to execute the query. The third parameter is the actual query to execute. The code is shown below:
```
flag = QryMethod(hQry, QRY_EXECUTE$, "select companyname from customers order by companyname")
```
Process the Results. After the query has successfully executed, the rows are available to BASIC+. The QRY_GETROW$ code (equated to 5 in XO_Equates) retrieves the next row from Access. QryMethod() is called with this code, and the results variable is built through a loop.
```
row = ""
results = ""
loop
  flag = QryMethod(hQry, QRY_GETROW$, row)
  while flag
    results<-1> = row
  repeat
```
Destroy the Query and Connection Objects, and populate the combo box. To prevent memory problems, the query and connection objects must be destroyed after use. The QRY_DESTROY$ code (equated to 1 in XO_Equates) passed to QryMethod() instructs the server to destroy the Query object. The XO_DESTROY$ code (also equated to 1 in XO_Equates) passed to XOMethod() instructs the server to destroy the Connection object, closing the connection. The Set_Property() call sets the LIST property of the combo box, populating it with the results of the query.
```
QryMethod(hQry, QRY_DESTROY$)
end
  
rv = Set_Property (@window : '.COMPANIES', 'LIST', results)
XOMethod(hXO, XO_DESTROY$)
 
end
```

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