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Command States

Commands can be in one of four states:

  • Initial ? No command text is set. A command is in this state after IDBCreateCommand::CreateCommand is called.

  • Unprepared ? The command text is set but the command is not prepared. A command is in this state after ICommandText::SetCommandText is called.

  • Prepared ? The command text is set and the command is prepared. A command is in this state after ICommandPrepare::Prepare is called.

  • Executed ? The command text is executed. A command is in this state after ICommand::Execute is called.

The following table lists each state and shows the value returned by each method in a command interface when it is called in that state. This table uses the following abbreviations:

  • OK = S_OK

  • NC = DB_E_NOCOMMAND

  • NP = DB_E_NOTPREPARED

  • OO = DB_E_OPENOBJECT

Method

Initial

Unprepared

Prepared

Executed

IColumnsInfo::GetColumnInfo

NC

OK (ICommandPrepare is not supported)

- or -

NP (ICommandPrepare is supported and the necessary information is not available to the command object)

OK

OK (ICommandPrepare is not supported)

- or -

NP (ICommandPrepare is supported and the necessary information is not available to the command object)

IColumnsInfo::MapColumnIDs

NC

OK (ICommandPrepare is not supported)

- or -

NP (ICommandPrepare is supported and the necessary information is not available to the command object)

OK

OK

(ICommandPrepare is not supported)

- or -

NP (ICommandPrepare is supported and the necessary information is not available to the command object)

IColumnsRowset::GetAvailableColumns

NC

OK (ICommandPrepare is not supported)

- or -

NP (ICommandPrepare is supported and the necessary information is not available to the command object)

OK

OK

(ICommandPrepare is not supported)

- or -

NP (ICommandPrepare is supported and the necessary information is not available to the command object)

IColumnsRowset::GetColumnsRowset

NC

OK (ICommandPrepare is not supported)

- or -

NP (ICommandPrepare is supported and the necessary information is not available to the command object)

OK

OK

(ICommandPrepare is not supported)

- or -

NP (ICommandPrepare is supported and the necessary information is not available to the command object)

ICommand::Cancel

OK

OK

OK

OK

ICommand::Execute

NC

OK

OK

OK

ICommand::GetDBSession

OK

OK

OK

OK

ICommandPrepare::Prepare

NC

OK

OK

OK (Execute did not create a rowset)

- or -

OO (Execute created a rowset, and the rowset is still open)

ICommandPrepare::Unprepare

OK

OK

OK

OK (Execute did not create a rowset)

- or -

OO (Execute created a rowset, and the rowset is still open)

ICommandProperties::GetProperties

OK

OK

OK

OK

ICommandProperties::SetProperties

OK

OK

OK

OK (Execute did not create a rowset)

- or -

OO (Execute created a rowset, and the rowset is still open)

ICommandText::GetCommandText

NC

OK

OK

OK

ICommandText::SetCommandText

OK

OK

OK

OK (Execute did not create a rowset)

- or -

OO (Execute created a rowset, and the rowset is still open)

ICommandWithParameters::GetParameterInfo

OK (SetParameterInfo has been called)

- or -

NC (SetParameterInfo has not been called)

OK (SetParameterInfo has been called)

- or -

NP (ICommandPrepare is supported, and SetParameterInfo has not been called)

OK

OK

ICommandWithParameters::MapParameterNames

OK (SetParameterInfo has been called)

- or -

NC (SetParameterInfo has not been called)

OK (SetParameterInfo has been called)

- or -

NP (ICommandPrepare is supported, and SetParameterInfo has not been called)

OK

OK

ICommandWithParameters::SetParameterInfo

OK

OK

OK

OK (Execute did not create a rowset)

- or -

OO (Execute created a rowset, and the rowset is still open)

The following figure illustrates the state transition for a command where the command text is set to an empty string and a non-empty string. Any call to ICommandText::SetCommandText with an empty command text must terminate in the Initial state, which is defined as command text not set. The only way to transition from Initial to Unprepared is to call ICommandText::SetCommandText with a non-empty command text. ICommand::Execute or ICommand::Prepare is called to transition to the Execute or Prepared states, respectively. In the Execute or Prepared states, calling ICommandText::SetCommandText with a non-empty command text returns the command to the Unprepared state, where the same call with a non-empty command text returns the command to the Unprepared state by using ICommandPrepare::Unprepare.