Microsoft Access 2010 : DATA ACCESS WITH ADO (part 2) - Creating Recordsets

3. Creating Recordsets

The examples provided so far have returned Recordset objects that were created implicitly as a result of the actions executed on the data source. The Open method of the Recordset object is used to retrieve the records from a data source and store them in the Recordset object. This method takes five parameters: Source, ConnectionString, CursorType, LockType, and Options. The Open method can be used in several different ways and this section will discuss a couple of examples for creating Recordset objects.

3.1. Creating a Recordset from a SQL Statement

A very common way to create a Recordset object is to open it directly from a SQL statement. Simply call the Open method with the SQL statement string and the connection and a new Recordset will be created.

Public Function OpenRecordsetFromSql() As ADODB.Recordset

    ' Define Variables
    Dim rs As New ADODB.Recordset

    ' Open the Recordset using a SQL statement
    rs.Open "SELECT [CONTACTS].* FROM [CONTACTS]", CurrentProject.AccessConnection

    ' Return the Recordset
    Set OpenRecordsetFromSql = rs

End Function

                                                       					  

In this case, the CurrentProject connection was supplied, but we could have easily created a Connection object to the desired source and supplied that instead.

3.2. Creating a Recordset from a Table or View

Another common way to create a Recordset object is to open it as a table or view. Simply call the Open method with the table or view name string and a new Recordset will be created for that object:

Public Function OpenRecordsetFromTable() As ADODB.Recordset

    ' Define Variables
    Dim rs As New ADODB.Recordset

    ' Open the Recordset using a SQL statement
    rs.Open "Contacts", CurrentProject.AccessConnection

    ' Return the Recordset
    Set OpenRecordsetFromView = rs

End Function

                                                       

The SQL statement used here is pretty run-of-the-mill, but ADO also provides a lot of flexibility for very complex statements and record types, as we will show next.

3.3. Creating a Shaped Recordset

A powerful feature of ADO is the ability to create shaped Recordset objects using the SQL language. Data shaping enables the developer to define the columns of a recordset, the relationships between them, and the manner in which the recordset is populated with data. This only works with providers that support MSDataShape, such as SQL Server.

The next example uses two tables with a parent-child relationship: Orders and Order Details. This code sample must be executed against a provider that supports the SQL Shape statement, like the SQL Server provider. Closely examine the following code, paying particular attention to the SQL statement:

Public Function OpenShapedRecordset() As ADODB.Recordset
    ' Define Variables
    Dim strSQL As String
    Dim cn     As New ADODB.Connection
    Dim rs     As New ADODB.Recordset

    ' Set the connection and open
    cn.ConnectionString = "<Your SQL Server Connection String>"
    cn.Provider = "MSDataShape"    ' We are using the MS Shape provider
    cn.CursorLocation = adUseClient
    cn.Open

    ' Create the SQL statement that builds the shaped Recordset
    strSQL = _
        "SHAPE" & _
            "{SELECT DISTINCT OrderID, CustomerID, OrderDate " & _

"FROM Orders " & _
            "WHERE OrderID BETWEEN 50 AND 70 " & _
            "ORDER BY OrderDate DESC} " & _
        "APPEND(" & _
            "{SELECT OrderID, ProductID, UnitPrice, Quantity " & _
            "FROM [Order Details]} AS CustomerOrders " & _
            "RELATE OrderID TO OrderID)"

    ' Open the Shaped Recordset
    rs.Open strSQL, cn

    ' Return the Recordset
    Set OpenShapedRecordset = rs

End Function

                                                   

In this SQL statement, the parent record is selected and then the child records are appended as a child Recordset object. Shaped Recordsets such as this are called hierarchical Recordsets. They exhibit a parent-child relationship in which the parent Recordset is the container in which the child Recordset is contained.

3.4. Creating a Recordset Containing Multiple Recordsets

There are many cases in which a command will generate a result containing multiple Recordset objects. When the Recordset object is returned, the first Recordset is already referenced by default. Each additional Recordset can be accessed by calling the NextRecordset method, which will return the next Recordset if it exists.

Public Function CreateMultiRecordset() As ADODB.Recordset

    ' Define Variables
    Dim rs     As New ADODB.Recordset
    Dim rsTemp As New ADODB.Recordset
    Dim strSQL As String

    ' Create the Multi Recordset SQL Statement and open the Recordset
    strSQL = "SELECT Prices.* FROM Prices; SELECT Contacts.* FROM Contacts"
    rs.Open strSQL, "<Provider that supports commands returning multi Recordsets>"

    ' Get the Next Recordset returned from the command
    Set rsTemp = rs.NextRecordset

    ' Return the Recordset
    Set CreateMultiRecordset = rs

End Function

                                                           					  

3.5. Verifying Recordset Options

The Supports method is used to verify the features (Recordset methods) that a specific ADO data provider supports for a Recordset object, which is determined by the provider and cursor type. The Supports method takes one parameter: CursorOptions, which is specified as a member of the CursorOptionEnum object. The method returns True if the option is supported, otherwise False. Consider the following code:

Public Function SupportsFind() As Boolean

   ' Define Variables
    Dim rs As New ADODB.Recordset

    ' Open the Recordset using to Contacts connection
    rs.Open "Contacts", CurrentProject.Connection

    ' Return whether or not the Find method is supported
    SupportsFind = rs.Supports(adFind)

End Function