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Command Object (ADO)

  • Стаття

Defines a specific command that you intend to execute against a data source.

Remarks

Use a Command object to query a database and return records in a Recordset object, to execute a bulk operation, or to manipulate the structure of a database. Depending on the functionality of the provider, some Command collections, methods, or properties may generate an error when they are referenced.

With the collections, methods, and properties of a Command object, you can do the following:

  • Define the executable text of the command (for example, a SQL statement) with the CommandText property. Alternatively, for command or query structures other than simple strings (for example, XML template queries) define the command with the CommandStream property.

  • Optionally, indicate the command dialect used in the CommandText or CommandStream with the Dialect property.

  • Define parameterized queries or stored-procedure arguments with Parameter objects and the Parameters collection.

  • Indicate whether parameter names should be passed to the provider with the NamedParameters property.

  • Execute a command and return a Recordset object if appropriate with the Execute method.

  • Specify the type of command with the CommandType property prior to execution to optimize performance.

  • Control whether the provider saves a prepared (or compiled) version of the command prior to execution with the Prepared property.

  • Set the number of seconds that a provider will wait for a command to execute with the CommandTimeout property.

  • Associate an open connection with a Command object by setting its ActiveConnection property.

  • Set the Name property to identify the Command object as a method on the associated Connection object.

  • Pass a Command object to the Source property of a Recordset to obtain data.

  • Access provider-specific attributes with the Properties collection.

Note

To execute a query without using a Command object, pass a query string to the Execute method of a Connection object or to the Open method of a Recordset object. However, a Command object is required when you want to persist the command text and re-execute it, or use query parameters.

To create a Command object independently of a previously defined Connection object, set its ActiveConnection property to a valid connection string. ADO still creates a Connection object, but it does not assign that object to an object variable. However, if you are associating multiple Command objects with the same connection, you should explicitly create and open a Connection object; this assigns the Connection object to an object variable. Make sure that the Connection object was opened successfully before you assign it to the ActiveConnection property of the Command object, because assigning a closed Connection object causes an error. If you do not set the ActiveConnection property of the Command object to this object variable, ADO creates a new Connection object for each Command object, even if you use the same connection string.

To execute a Command, call it by its Name property on the associated Connection object. The Command must have its ActiveConnection property set to the Connection object. If the Command has parameters, pass their values as arguments to the method.

If two or more Command objects are executed on the same connection and either Command object is a stored procedure with output parameters, an error occurs. To execute each Command object, use separate connections or disconnect all other Command objects from the connection.

The Parameters collection is the default member of the Command object. As a result, the following two code statements are equivalent.

objCmd.Parameters.Item(0)  
objCmd(0)
  • The Command object is not safe for scripting.

This section contains the following topic.

See Also

Connection Object (ADO)
Parameters Collection (ADO)
Properties Collection (ADO)
Appendix A: Providers