You must set the Type property of a Parameter object before appending it to the Parameters collection. If you select a variable-length data type, you must also set the Size property to a value greater than zero.

Describing parameters yourself minimizes calls to the provider and therefore improves performance when you use stored procedures or parameterized queries. However, you must know the properties of the parameters associated with the stored procedure or parameterized query that you want to call.

Use the CreateParameter method to create Parameter objects with the appropriate property settings and use the Append method to add them to the Parameters collection. This lets you set and return parameter values without having to call the provider for the parameter information. If you are writing to a provider that does not supply parameter information, you must use this method to manually populate the Parameters collection in order to use parameters at all.

The FieldValue parameter is only valid when adding a Field object to a Record object, not to a Recordset object. With a Record object, you can append fields and provide values at the same time. With a Recordset object, you must create fields while the Recordset is closed, and then open the Recordset and assign values to the fields.

Note

For new Field objects that have been appended to the Fields collection of a Record object, the Value property must be set before any other Field properties can be specified. First, a specific value for the Value property must have been assigned and Update on the Fields collection called. Then, other properties such as Type or Attributes can be accessed. Field objects of the following data types (DataTypeEnum) cannot be appended to the Fields collection and will cause an error to occur: adArray, adChapter, adEmpty, adPropVariant, and adUserDefined. Also, the following data types are not supported by ADO: adIDispatch, adIUnknown, and adIVariant. For these types, no error will occur when appended, but usage can produce unpredictable results including memory leaks.

If you do not set the CursorLocation property before calling the Append method, CursorLocation will be set to adUseClient (a CursorLocationEnum value) automatically when the Open method of the Recordset object is called.

A run-time error will occur if the Append method is called on the Fields collection of an open Recordset, or on a Recordset where the ActiveConnection property has been set. You can only append fields to a Recordset that is not open and has not yet been connected to a data source. This is typically the case when a Recordset object is fabricated with the CreateRecordset method or assigned to an object variable.

A run-time error will not occur if the Append method is called on the Fields collection of an open Record. The new field will be added to the Fields collection of the Record object. If the Record was derived from a Recordset, the new field will not appear in the Fields collection of the Recordset object.

A non-existent field can be created and appended to the Fields collection by assigning a value to the field object as if it already existed in the collection. The assignment will trigger the automatic creation and appending of the Field object, and then the assignment will be completed.

After appending a Field to the Fields collection of a Record object, call the Update method of the Fields collection to save the change.