The LA Fox Developer Newsletter

February 2000

ADO Quickstart (Con't from page 7) when using Remote Data Services (RDS)

Any additional arguments passed in the ConnectionString are passed through to the OLE DB provider being used. In addition to the Open method, the following are the common methods you are likely to use with the Connection object:

+ BeginTrans, CommiTrans, and RollBackTrans—These methods work like the Begin Transaction, End Transaction, and RollBack statements in Visual FoxPro. The Connection object controls all transaction processing. For more detail, see the section Transactions/Updating Data. Note that not all OLE DB providers support transaction processing.

+ Close—This method closes an open Connection object.

+ Execute—This method runs a SQL statement, stored procedure, or OLE DB provider-specific command. In reality, a Command object, which actually does the work of executing the command, is created on the fly. More on the Command object and the flat object hierarchy of ADO later in this paper.

+ OpenSchema—This method returns information regarding defined tables, fields, catalogs, and views into an ADO Recordset object. This method works like the DBGetProp() function in Visual FoxPro.

Errors collection

ADO does not trap errors, nor does it have an error handler. Instead, ADO can record the occasions when errors occur. It is up to the host application, Visual FoxPro in this case, to both trap and handle the error. ADO only reports what errors have occurred. Note that the error is actually reported by the specific OLE DB provider. ADO is merely a vehicle to report the error.

The Errors collection is part of the Connection object and consists of zero or more Error objects. When an error occurs, an Error object is appended to the Errors collection. The following code illustrates how the Errors collection works. In this example, the name of the database has been misspelled purposely in order to generate an error:

oConnection = CreateObJect(”adodb.connection”)
With oConnection

Provider = “SQLOLEDB.1”
.connectionStrlng = “Persist Security Info=False;User
ID=sa;Initlal Catalog=Nothwind;Data Source=JVP”
.Open

EndWith

*~ At this point an error will occur — causing VFP’s default error

For Each Error In oConnection.Errors
?Error.Description,Error.Number

Next Error

Recordset Object

ProgID: ADODB.Recordset

Once you establish an ADO connection, you can open a recordset of data. The Recordset object is very much like a Visual FoxPro cursor. Like the Visual FoxPro cursor, an ADO recordset consists of rows of data. The recordset is the primary object that you will use while working with ADO. Like the Connection object, the Recordset object also provides an Open method. To illustrate, the following code opens the Customer table of the Visual FoxPro Tastrade database:

oRecordSet = C reateObject( “adodb.recordset”)
oRecordSet.Open(”Select * From Customer” oConnection)

The first argument of the Open method specifies the source of data. As you will see, the source can take on several forms. The second argument of the Open method specifies a connection to use for retrieving the data specified by the source. At a minimum, this is all you need to open a recordset. Additional examples will expand on the additional arguments the Open method accepts.

With a Recordset object created, one of the most common actions you will perform is navigating through records. Depending on the type of ADO recordset that has been created, certain navigational capabilities may or may not be available. The different types of possible ADO recordsets will be discussed shortly. The following code illustrates how to navigate through an ADO recordset:

Do While IoRecordSet.Eof

oRecordset.MoveNext

EndDo

The following paragraphs briefly describe the most common recordset properties and methods you are likely to use. It is by no means a replacement for the ADO documentation, which gives both a complete description of the properties and methods and complete descriptions of acceptable enumerated types and arguments. ADO is well documented in the Microsoft Data Access Components (MDAC) SDK. You can download the MDAC SDK from http://www.microsoft.com/data/mdac2.htm

(Con't, page 9)

Page 8