CDaoWorkspace Class

Bài viết
05/16/2022

Manages a named, password-protected database session from login to logoff, by a single user.

Note

Data Access Objects (DAO) is supported through Office 2013. DAO 3.6 is the final version, and it's considered obsolete.

Syntax

class CDaoWorkspace : public CObject

Members

Public Constructors

Name	Description
CDaoWorkspace::CDaoWorkspace	Constructs a workspace object. Afterwards, call `Create` or `Open`.

Public Methods

Name	Description
CDaoWorkspace::Append	Appends a newly created workspace to the database engine's Workspaces collection.
CDaoWorkspace::BeginTrans	Begins a new transaction, which applies to all databases open in the workspace.
CDaoWorkspace::Close	Closes the workspace and all of the objects it contains. Pending transactions are rolled back.
CDaoWorkspace::CommitTrans	Completes the current transaction and saves the changes.
CDaoWorkspace::CompactDatabase	Compacts (or duplicates) a database.
CDaoWorkspace::Create	Creates a new DAO workspace object.
CDaoWorkspace::GetDatabaseCount	Returns the number of DAO database objects in the workspace's Databases collection.
CDaoWorkspace::GetDatabaseInfo	Returns information about a specified DAO database defined in the workspace's Databases collection.
CDaoWorkspace::GetIniPath	Returns the location of the Microsoft Jet database engine's initialization settings in the Windows registry.
CDaoWorkspace::GetIsolateODBCTrans	Returns a value that indicates whether multiple transactions that involve the same ODBC data source are isolated via forced multiple connections to the data source.
CDaoWorkspace::GetLoginTimeout	Returns the number of seconds before an error occurs when the user attempts to log in to an ODBC database.
CDaoWorkspace::GetName	Returns the user-defined name for the workspace object.
CDaoWorkspace::GetUserName	Returns the user name specified when the workspace was created. This is the name of the workspace owner.
CDaoWorkspace::GetVersion	Returns a string that contains the version of the database engine associated with the workspace.
CDaoWorkspace::GetWorkspaceCount	Returns the number of DAO workspace objects in the database engine's Workspaces collection.
CDaoWorkspace::GetWorkspaceInfo	Returns information about a specified DAO workspace defined in the database engine's Workspaces collection.
CDaoWorkspace::Idle	Allows the database engine to perform background tasks.
CDaoWorkspace::IsOpen	Returns nonzero if the workspace is open.
CDaoWorkspace::Open	Explicitly opens a workspace object associated with DAO's default workspace.
CDaoWorkspace::RepairDatabase	Attempts to repair a damaged database.
CDaoWorkspace::Rollback	Ends the current transaction and doesn't save the changes.
CDaoWorkspace::SetDefaultPassword	Sets the password that the database engine uses when a workspace object is created without a specific password.
CDaoWorkspace::SetDefaultUser	Sets the user name that the database engine uses when a workspace object is created without a specific user name.
CDaoWorkspace::SetIniPath	Sets the location of the Microsoft Jet database engine's initialization settings in the Windows registry.
CDaoWorkspace::SetIsolateODBCTrans	Specifies whether multiple transactions that involve the same ODBC data source are isolated by forcing multiple connections to the data source.
CDaoWorkspace::SetLoginTimeout	Sets the number of seconds before an error occurs when the user attempts to log in to an ODBC data source.

Public Data Members

Name	Description
CDaoWorkspace::m_pDAOWorkspace	Points to the underlying DAO workspace object.

Remarks

In most cases, you won't need multiple workspaces, and you won't need to create explicit workspace objects; when you open database and recordset objects, they use DAO's default workspace. However, if needed, you can run multiple sessions at a time by creating more workspace objects. Each workspace object can contain multiple open database objects in its own Databases collection. In MFC, a workspace is primarily a transaction manager, specifying a set of open databases all in the same "transaction space."

Note

The DAO database classes are distinct from the MFC database classes based on Open Database Connectivity (ODBC). All DAO database class names have a "CDao" prefix. In general, the MFC classes based on DAO are more capable than the MFC classes based on ODBC. The DAO-based classes access data through the Microsoft Jet database engine, including ODBC drivers. They also support Data Definition Language (DDL) operations, such as creating databases and adding tables and fields via the classes, without having to call DAO directly.

Capabilities

Class CDaoWorkspace provides:

Explicit access, if needed, to a default workspace, created by initializing the database engine. Usually you use DAO's default workspace implicitly by creating database and recordset objects.
A transaction space in which transactions apply to all databases open in the workspace. You can create more workspaces to manage separate transaction spaces.
An interface to many properties of the underlying Microsoft Jet database engine (see the static member functions). Opening or creating a workspace, or calling a static member function before open or create, initializes the database engine.
Access to the database engine's Workspaces collection, which stores all active workspaces that have been appended to it. You can also create and work with workspaces without appending them to the collection.

Security

MFC doesn't implement the Users and Groups collections in DAO, which are used for security control. If you need those aspects of DAO, you must program them yourself via direct calls to DAO interfaces. For information, see Technical Note 54.

Usage

You can use class CDaoWorkspace to:

Explicitly open the default workspace.

Usually your use of the default workspace is implicit when you open new CDaoDatabase or CDaoRecordset objects. But you might need to access it explicitly. For example, to access database engine properties or the Workspaces collection. See "Implicit Use of the Default Workspace" below.
Create new workspaces. Call Append if you want to add them to the Workspaces collection.
Open an existing workspace in the Workspaces collection.

Creating a new workspace that doesn't already exist in the Workspaces collection is described under the Create member function. Workspace objects don't persist in any way between database engine sessions. If your application links MFC statically, ending the application uninitializes the database engine. If your application links with MFC dynamically, the database engine is uninitialized when the MFC DLL is unloaded.

Explicitly opening the default workspace, or opening an existing workspace in the Workspaces collection, is described under the Open member function.

End a workspace session by closing the workspace with the Close member function. Close closes any databases you haven't closed and rolls back any uncommitted transactions.

Transactions

DAO manages transactions at the workspace level; hence, transactions on a workspace with multiple open databases apply to all of the databases. For example, if two databases have uncommitted updates and you call CommitTrans, all of the updates are committed. If you want to limit transactions to a single database, you need a separate workspace object for it.

Implicit Use of the Default Workspace

MFC uses DAO's default workspace implicitly under the following circumstances:

If you create a new CDaoDatabase object but don't do so through an existing CDaoWorkspace object, MFC creates a temporary workspace object for you, which corresponds to DAO's default workspace. If you do so for multiple databases, all of the database objects are associated with the default workspace. You can access a database's workspace through a CDaoDatabase data member.
Similarly, if you create a CDaoRecordset object without supplying a pointer to a CDaoDatabase object, MFC creates a temporary database object and, by extension, a temporary workspace object. You can access a recordset's database, and indirectly its workspace, through a CDaoRecordset data member.

Other Operations

Other database operations are also provided, such as repairing a corrupted database or compacting a database.

For information about calling DAO directly and about DAO security, see Technical Note 54.

Inheritance Hierarchy

CObject

CDaoWorkspace

Requirements

Header: afxdao.h

CDaoWorkspace::Append

Call this member function after you call Create.

virtual void Append();

Remarks

Append appends a newly created workspace object to the database engine's Workspaces collection. Workspaces don't persist between database engine sessions; they're stored only in memory, not on disk. You don't have to append a workspace; if you don't, you can still use it.

An appended workspace remains in the Workspaces collection, in an active, open state, until you call its Close member function.

For related information, see the topic "Append Method" in DAO Help.

CDaoWorkspace::BeginTrans

Call this member function to initiate a transaction.

void BeginTrans();

Remarks

After you call BeginTrans, updates you make to your data or database structure take effect when you commit the transaction. Because the workspace defines a single transaction space, the transaction applies to all open databases in the workspace. There are two ways to complete the transaction:

Call the CommitTrans member function to commit the transaction and save changes to the data source.
Or call the Rollback member function to cancel the transaction.

Closing the workspace object or a database object while a transaction is pending rolls back all pending transactions.

If you need to isolate transactions on one ODBC data source from those on another ODBC data source, see the SetIsolateODBCTrans member function.

CDaoWorkspace::CDaoWorkspace

Constructs a CDaoWorkspace object.

CDaoWorkspace();

Remarks

After constructing the C++ object, you have two options:

Call the object's Open member function to open the default workspace or to open an existing object in the Workspaces collection.
Or call the object's Create member function to create a new DAO workspace object. This explicitly starts a new workspace session, which you can refer to via the CDaoWorkspace object. After calling Create, you can call Append if you want to add the workspace to the database engine's Workspaces collection.

See the class overview for CDaoWorkspace for information about when you need to explicitly create a CDaoWorkspace object. Usually, you use workspaces created implicitly when you open a CDaoDatabase object without specifying a workspace or when you open a CDaoRecordset object without specifying a database object. MFC DAO objects created in this way use DAO's default workspace, which is created once and reused.

To release a workspace and its contained objects, call the workspace object's Close member function.

CDaoWorkspace::Close

Call this member function to close the workspace object.

virtual void Close();

Remarks

Closing an open workspace object releases the underlying DAO object and, if the workspace is a member of the Workspaces collection, removes it from the collection. Calling Close is good programming practice.

Caution

Closing a workspace object closes any open databases in the workspace. This results in any recordsets open in the databases being closed as well, and any pending edits or updates are rolled back. For related information, see the CDaoDatabase::Close, CDaoRecordset::Close, CDaoTableDef::Close, and CDaoQueryDef::Close member functions.

Workspace objects aren't permanent; they only exist while references to them exist. This means that when the database engine session ends, the workspace, and its Databases collection don't persist. You must re-create them for the next session by opening your workspace and database(s) again.

For related information, see the topic "Close Method" in DAO Help.

CDaoWorkspace::CommitTrans

Call this member function to commit a transaction which saves a group of edits and updates to one or more databases in the workspace.

void CommitTrans();

Remarks

A transaction consists of a series of changes to the database's data or its structure, beginning with a call to BeginTrans. When you complete the transaction, either commit it or roll it back (cancel the changes) with Rollback. By default, without transactions, updates to records are committed immediately. Calling BeginTrans causes commitment of updates to be delayed until you call CommitTrans.

Caution

Within one workspace, transactions are always global to the workspace and aren't limited to only one database or recordset. If you perform operations on more than one database or recordset within a workspace transaction, CommitTrans commits all pending updates, and Rollback restores all operations on those databases and recordsets.

When you close a database or workspace with pending transactions, the transactions are all rolled back.

Note

This isn't a two-phase commit mechanism. If one update fails to commit, others still will commit.

CDaoWorkspace::CompactDatabase

Call this member function to compact a specified Microsoft Jet (.MDB) database.

static void PASCAL CompactDatabase(
    LPCTSTR lpszSrcName,
    LPCTSTR lpszDestName,
    LPCTSTR lpszLocale = dbLangGeneral,
    int nOptions = 0);

static void PASCAL CompactDatabase(
    LPCTSTR lpszSrcName,
    LPCTSTR lpszDestName,
    LPCTSTR lpszLocale,
    int nOptions,
    LPCTSTR lpszPassword);

Parameters

lpszSrcName
The name of an existing, closed database. It can be a full path and filename, such as "C:\\MYDB.MDB". If the filename has an extension, you must specify it. If your network supports the uniform naming convention (UNC), you can also specify a network path, such as "\\\\MYSERVER\\MYSHARE\\MYDIR\\MYDB.MDB". (Double backslashes are required in the path strings because "\" is the C++ escape character.)

lpszDestName
The full path of the compacted database that you are creating. You can also specify a network path as with lpszSrcName. You can't use the lpszDestName argument to specify the same database file as lpszSrcName.

lpszPassword
A password, used when you want to compact a password-protected database. If you use the version of CompactDatabase that takes a password, you must supply all parameters. Also, because this is a connect parameter, it requires special formatting, as follows: ;PWD= lpszPassword. For example: ;PWD="Happy". (The leading semicolon is required.)

lpszLocale
A string expression used to specify collating order for creating lpszDestName. If you omit this argument by accepting the default value of dbLangGeneral (see below), the locale of the new database is the same as the old database. Possible values are:

dbLangGeneral English, German, French, Portuguese, Italian, and Modern Spanish
dbLangArabic Arabic
dbLangCyrillic Russian
dbLangCzech Czech
dbLangDutch Dutch
dbLangGreek Greek
dbLangHebrew Hebrew
dbLangHungarian Hungarian
dbLangIcelandic Icelandic
dbLangNordic Nordic languages (Microsoft Jet database engine version 1.0 only)
dbLangNorwdan Norwegian and Danish
dbLangPolish Polish
dbLangSpanish Traditional Spanish
dbLangSwedfin Swedish and Finnish
dbLangTurkish Turkish

nOptions
Indicates one or more options for the target database, lpszDestName. If you omit this argument by accepting the default value, the lpszDestName has the same encryption and the same version as lpszSrcName. You can combine the dbEncrypt or dbDecrypt option with one of the version options using the bitwise-OR operator. Possible values, which specify a database format, not a database engine version, are:

dbEncrypt Encrypt the database while compacting.
dbDecrypt Decrypt the database while compacting.
dbVersion10 Create a database that uses the Microsoft Jet database engine version 1.0 while compacting.
dbVersion11 Create a database that uses the Microsoft Jet database engine version 1.1 while compacting.
dbVersion20 Create a database that uses the Microsoft Jet database engine version 2.0 while compacting.
dbVersion30 Create a database that uses the Microsoft Jet database engine version 3.0 while compacting.

You can use dbEncrypt or dbDecrypt in the options argument to specify whether to encrypt or to decrypt the database as it is compacted. If you omit an encryption constant or if you include both dbDecrypt and dbEncrypt, lpszDestName has the same encryption as lpszSrcName. You can use one of the version constants in the options argument to specify the version of the data format for the compacted database. This constant affects only the version of the data format of lpszDestName. You can specify only one version constant. If you omit a version constant, lpszDestName will have the same version as lpszSrcName. You can compact lpszDestName only to a version that is the same or later than lpszSrcName.

Caution

If a database isn't encrypted, it is possible, even if you implement user/password security, to directly read the binary disk file that constitutes the database.

Remarks

As you change data in a database, the database file can become fragmented and use more disk space than necessary. Periodically, you should compact your database to defragment the database file. The compacted database is usually smaller. You can also choose to change the collating order, the encryption, or the version of the data format while you copy and compact the database.

Caution

The CompactDatabase member function won't correctly convert a complete Microsoft Access database from one version to another. Only the data format is converted. Microsoft Access-defined objects, such as forms and reports, aren't converted. However, the data is correctly converted.

Tip

You can also use CompactDatabase to copy a database file.

For more information about compacting databases, see the topic "CompactDatabase Method" in DAO Help.

CDaoWorkspace::Create

Call this member function to create a new DAO workspace object and associate it with the MFC CDaoWorkspace object.

virtual void Create(
    LPCTSTR lpszName,
    LPCTSTR lpszUserName,
    LPCTSTR lpszPassword);

Parameters

lpszName
A string with up to 14 characters that uniquely names the new workspace object. You must supply a name. For related information, see the topic "Name Property" in DAO Help.

lpszUserName
The user name of the workspace's owner. For requirements, see the lpszDefaultUser parameter to the SetDefaultUser member function. For related information, see the topic "UserName Property" in DAO Help.

lpszPassword
The password for the new workspace object. A password can be up to 14 characters long and can contain any character except ASCII 0 (null). Passwords are case-sensitive. For related information, see the topic "Password Property" in DAO Help.

Remarks

The overall creation process is:

Construct a CDaoWorkspace object.
Call the object's Create member function to create the underlying DAO workspace. You must specify a workspace name.
Optionally call Append if you want to add the workspace to the database engine's Workspaces collection. You can work with the workspace without appending it.

After the Create call, the workspace object is in an open state, ready for use. You don't call Open after Create. You don't call Create if the workspace already exists in the Workspaces collection. Create initializes the database engine if it hasn't already been initialized for your application.

CDaoWorkspace::GetDatabaseCount

Call this member function to retrieve the number of DAO database objects in the workspace's Databases collection. Which is the number of open databases in the workspace.

short GetDatabaseCount();

Return Value

The number of open databases in the workspace.

Remarks

GetDatabaseCount is useful if you need to loop through all defined databases in the workspace's Databases collection. To obtain information about a given database in the collection, see GetDatabaseInfo. Typical usage is to call GetDatabaseCount for the number of open databases, then use that number as a loop index for repeated calls to GetDatabaseInfo.

CDaoWorkspace::GetDatabaseInfo

Call this member function to obtain various kinds of information about a database open in the workspace.

void GetDatabaseInfo(
    int nIndex,
    CDaoDatabaseInfo& dbinfo,
    DWORD dwInfoOptions = AFX_DAO_PRIMARY_INFO);

void GetDatabaseInfo(
    LPCTSTR lpszName,
    CDaoDatabaseInfo& dbinfo,
    DWORD dwInfoOptions = AFX_DAO_PRIMARY_INFO);

Parameters

nIndex
The zero-based index of the database object in the workspace's Databases collection, for lookup by index.

dbinfo
A reference to a CDaoDatabaseInfo object that returns the information requested.

dwInfoOptions
Options that specify which information about the database to retrieve. The available options are listed here along with what they cause the function to return:

AFX_DAO_PRIMARY_INFO (Default) Name, Updatable, Transactions
AFX_DAO_SECONDARY_INFO Primary information plus: Version, Collating Order, Query Timeout
AFX_DAO_ALL_INFO Primary and secondary information plus: Connect

lpszName
The name of the database object, for lookup by name. The name is a string with up to 14 characters that uniquely names the new workspace object.

Remarks

One version of the function lets you look up a database by index. The other version lets you look up a database by name.

For a description of the information returned in dbinfo, see the CDaoDatabaseInfo structure. This structure has members that correspond to the items of information listed above in the description of dwInfoOptions. When you request information at one level, you get information for any prior levels as well.

CDaoWorkspace::GetIniPath

Call this member function to obtain the location of the Microsoft Jet database engine's initialization settings in the Windows registry.

static CString PASCAL GetIniPath();

Return Value

A CString containing the registry location.

Remarks

You can use the location to obtain information about settings for the database engine. The information returned is actually the name of a registry subkey.

For related information, see the topics "IniPath Property" and "Customizing Windows Registry Settings for Data Access" in DAO Help.

CDaoWorkspace::GetIsolateODBCTrans

Call this member function to get the current value of the DAO IsolateODBCTrans property for the workspace.

BOOL GetIsolateODBCTrans();

Return Value

Nonzero if ODBC transactions are isolated; otherwise 0.

Remarks

In some situations, you might need to have multiple simultaneous transactions pending on the same ODBC database. To do this, you need to open a separate workspace for each transaction. Keep in mind that although each workspace can have its own ODBC connection to the database, this slows system performance. Because transaction isolation isn't normally required, ODBC connections from multiple workspace objects opened by the same user are shared by default.

Some ODBC servers, such as Microsoft SQL Server, don't allow simultaneous transactions on a single connection. If you need to have more than one transaction at a time pending against such a database, set the IsolateODBCTrans property to TRUE on each workspace as soon as you open it. This forces a separate ODBC connection for each workspace.

For related information, see the topic "IsolateODBCTrans Property" in DAO Help.

CDaoWorkspace::GetLoginTimeout

Call this member function to get the current value of the DAO LoginTimeout property for the workspace.

static short PASCAL GetLoginTimeout();

Return Value

The number of seconds before an error occurs when you attempt to log in to an ODBC database.

Remarks

This value represents the number of seconds before an error occurs when you attempt to log in to an ODBC database. The default LoginTimeout setting is 20 seconds. When LoginTimeout is set to 0, no timeout occurs and the communication with the data source might stop responding.

When you are attempting to log in to an ODBC database, such as Microsoft SQL Server, the connection may fail as a result of network errors or because the server isn't running. Rather than waiting for the default 20 seconds to connect, you can specify how long the database engine waits before it produces an error. Logging in to the server happens implicitly as part of different events, such as running a query on an external server database.

For related information, see the topic "LoginTimeout Property" in DAO Help.

CDaoWorkspace::GetName

Call this member function to get the user-defined name of the DAO workspace object underlying the CDaoWorkspace object.

CString GetName();

Return Value

A CString containing the user-defined name of the DAO workspace object.

Remarks

The name is useful for accessing the DAO workspace object in the database engine's Workspaces collection by name.

For related information, see the topic "Name Property" in DAO Help.

CDaoWorkspace::GetUserName

Call this member function to obtain the name of the owner of the workspace.

CString GetUserName();

Return Value

A CString that represents the owner of the workspace object.

Remarks

To get or set the permissions for the workspace owner, call DAO directly to check the Permissions property setting; this determines what permissions that user has. To work with permissions, you need a SYSTEM.MDA file.

For information about calling DAO directly, see Technical Note 54. For related information, see the topic "UserName Property" in DAO Help.

CDaoWorkspace::GetVersion

Call this member function to determine the version of the Microsoft Jet database engine in use.

static CString PASCAL GetVersion();

Return Value

A CString that indicates the version of the database engine associated with the object.

Remarks

The value returned represents the version number in the form "major.minor"; for example, "3.0". The product version number (for example, 3.0) consists of the version number (3), a period, and the release number (0).

For related information, see the topic "Version Property" in DAO Help.

CDaoWorkspace::GetWorkspaceCount

Call this member function to retrieve the number of DAO workspace objects in the database engine's Workspaces collection.

short GetWorkspaceCount();

Return Value

The number of open workspaces in the Workspaces collection.

Remarks

This count doesn't include any open workspaces not appended to the collection. GetWorkspaceCount is useful if you need to loop through all defined workspaces in the Workspaces collection. To obtain information about a given workspace in the collection, see GetWorkspaceInfo. Typical usage is to call GetWorkspaceCount for the number of open workspaces, then use that number as a loop index for repeated calls to GetWorkspaceInfo.

CDaoWorkspace::GetWorkspaceInfo

Call this member function to obtain various kinds of information about a workspace open in the session.

void GetWorkspaceInfo(
    int nIndex,
    CDaoWorkspaceInfo& wkspcinfo,
    DWORD dwInfoOptions = AFX_DAO_PRIMARY_INFO);

void GetWorkspaceInfo(
    LPCTSTR lpszName,
    CDaoWorkspaceInfo& wkspcinfo,
    DWORD dwInfoOptions = AFX_DAO_PRIMARY_INFO);

Parameters

nIndex
The zero-based index of the database object in the Workspaces collection, for lookup by index.

wkspcinfo
A reference to a CDaoWorkspaceInfo object that returns the information requested.

dwInfoOptions
Options that specify which information about the workspace to retrieve. The available options are listed here along with what they cause the function to return:

AFX_DAO_PRIMARY_INFO (Default) Name
AFX_DAO_SECONDARY_INFO Primary information plus: User Name
AFX_DAO_ALL_INFO Primary and secondary information plus: Isolate ODBCTrans

lpszName
The name of the workspace object, for lookup by name. The name is a string with up to 14 characters that uniquely names the new workspace object.

Remarks

For a description of the information returned in wkspcinfo, see the CDaoWorkspaceInfo structure. This structure has members that correspond to the items of information listed above in the description of dwInfoOptions. When you request information at one level, you get information for prior levels as well.

CDaoWorkspace::Idle

Call Idle to provide the database engine with the opportunity to perform background tasks that may not be up-to-date because of intense data processing.

static void PASCAL Idle(int nAction = dbFreeLocks);

Parameters

nAction
An action to take during the idle processing. Currently the only valid action is dbFreeLocks.

Remarks

This is often true in multiuser, multitasking environments in which there isn't enough background processing time to keep all records in a recordset current.

Note

Calling Idle isn't necessary with databases created with version 3.0 of the Microsoft Jet database engine. Use Idle only for databases created with earlier versions.

Usually, read locks are removed and data in local dynaset-type recordset objects is updated only when no other actions (including mouse movements) are occurring. If you periodically call Idle, you provide the database engine with time to catch up on background processing tasks by releasing unneeded read locks. Specifying the dbFreeLocks constant as an argument delays processing until all read locks are released.

This member function isn't needed in single-user environments unless multiple instances of an application are running. The Idle member function may increase performance in a multiuser environment because it forces the database engine to flush data to disk, releasing locks on memory. You can also release read locks by making operations part of a transaction.

For related information, see the topic "Idle Method" in DAO Help.

CDaoWorkspace::IsOpen

Call this member function to determine whether the CDaoWorkspace object is open. Which means either the MFC object has been initialized by a call to Open or a call to Create.

BOOL IsOpen() const;

Return Value

Nonzero if the workspace object is open; otherwise 0.

Remarks

You can call any of the member functions of a workspace that is in an open state.

CDaoWorkspace::m_pDAOWorkspace

A pointer to the underlying DAO workspace object.

Remarks

Use this data member if you need direct access to the underlying DAO object. You can call the DAO object's interfaces through this pointer.

For information about accessing DAO objects directly, see Technical Note 54.

CDaoWorkspace::Open

Explicitly opens a workspace object associated with DAO's default workspace.

virtual void Open(LPCTSTR lpszName = NULL);

Parameters

lpszName
The name of the DAO workspace object to open — a string with up to 14 characters that uniquely names the workspace. Accept the default value NULL to explicitly open the default workspace. For naming requirements, see the lpszName parameter for Create. For related information, see the topic "Name Property" in DAO Help.

Remarks

After constructing a CDaoWorkspace object, call this member function to do one of:

Explicitly open the default workspace. Pass NULL for lpszName.
Open an existing CDaoWorkspace object, a member of the Workspaces collection, by name. Pass a valid name for an existing workspace object.

Open puts the workspace object into an open state and also initializes the database engine if it hasn't already been initialized for your application.

Although many CDaoWorkspace member functions can only be called after the workspace is opened, the following member functions, which operate on the database engine, are available after construction of the C++ object but before a call to Open:

Create
GetIniPath
GetLoginTimeout

GetVersion
Idle

SetDefaultPassword
SetDefaultUser

SetIniPath
SetLoginTimeout

CDaoWorkspace::RepairDatabase

Call this member function if you need to attempt to repair a corrupted database that accesses the Microsoft Jet database engine.

static void PASCAL RepairDatabase(LPCTSTR lpszName);

Parameters

lpszName
The path and filename for an existing Microsoft Jet engine database file. If you omit the path, only the current directory is searched. If your system supports the uniform naming convention (UNC), you can also specify a network path, such as: "\\\\MYSERVER\\MYSHARE\\MYDIR\\MYDB.MDB". (Double backslashes are required in the path string because "\" is the C++ escape character.)

Remarks

You must close the database specified by lpszName before you repair it. In a multiuser environment, other users can't have lpszName open while you are repairing it. If lpszName isn't closed or isn't available for exclusive use, an error occurs.

This member function attempts to repair a database that was marked as possibly corrupt by an incomplete write operation. This can occur if an application using the Microsoft Jet database engine is closed unexpectedly because of a power outage or computer hardware problem. If you complete the operation and call the Close member function or you quit the application in a usual way, the database won't be marked as possibly corrupt.

Note

After repairing a database, it is also a good idea to compact it using the CompactDatabase member function to defragment the file and to recover disk space.

For more information about repairing databases, see the topic "RepairDatabase Method" in DAO Help.

CDaoWorkspace::Rollback

Call this member function to end the current transaction and restore all databases in the workspace to their condition before the transaction was begun.

void Rollback();

Remarks

Caution

Within one workspace object, transactions are always global to the workspace and aren't limited to only one database or recordset. If you perform operations on more than one database or recordset within a workspace transaction, Rollback restores all operations on all of those databases and recordsets.

If you close a workspace object without saving or rolling back any pending transactions, the transactions are automatically rolled back. If you call CommitTrans or Rollback without first calling BeginTrans, an error occurs.

Note

When you begin a transaction, the database engine records its operations in a file kept in the directory specified by the TEMP environment variable on the workstation. If the transaction log file exhausts the available storage on your TEMP drive, the database engine will cause MFC to throw a CDaoException (DAO error 2004). At this point, if you call CommitTrans, an indeterminate number of operations are committed but the remaining uncompleted operations are lost, and the operation has to be restarted. Calling Rollback releases the transaction log and rolls back all operations in the transaction.

CDaoWorkspace::SetDefaultPassword

Call this member function to set the default password that the database engine uses when a workspace object is created without a specific password.

static void PASCAL SetDefaultPassword(LPCTSTR lpszPassword);

Parameters

lpszPassword
The default password. A password can be up to 14 characters long and can contain any character except ASCII 0 (null). Passwords are case-sensitive.

Remarks

The default password that you set applies to new workspaces you create after the call. When you create subsequent workspaces, you don't need to specify a password in the Create call.

To use this member function:

Construct a CDaoWorkspace object but don't call Create.
Call SetDefaultPassword and, if you like, SetDefaultUser.
Call Create for this workspace object or subsequent ones, without specifying a password.

By default, the DefaultUser property is set to "admin" and the DefaultPassword property is set to an empty string ("").

For more about security, see the topic "Permissions Property" in DAO Help. For related information, see the topics "DefaultPassword Property" and "DefaultUser Property" in DAO Help.

CDaoWorkspace::SetDefaultUser

Call this member function to set the default user name that the database engine uses when a workspace object is created without a specific user name.

static void PASCAL SetDefaultUser(LPCTSTR lpszDefaultUser);

Parameters

lpszDefaultUser
The default user name. A user name can be 1 - 20 characters long and include alphabetic characters, accented characters, numbers, spaces, and symbols except for: " (quotation marks), / (forward slash), \ (backslash), [ ] (brackets), : (colon), | (pipe), < (less-than sign), > (greater-than sign), + (plus sign), = (equal sign), ; (semicolon), , ( comma), (question mark), * (asterisk), leading spaces, and control characters (ASCII 00 to ASCII 31). For related information, see the topic "UserName Property" in DAO Help.

Remarks

The default user name that you set applies to new workspaces you create after the call. When you create subsequent workspaces, you don't need to specify a user name in the Create call.

To use this member function:

Construct a CDaoWorkspace object but don't call Create.
Call SetDefaultUser and, if you like, SetDefaultPassword.
Call Create for this workspace object or subsequent ones, without specifying a user name.

By default, the DefaultUser property is set to "admin" and the DefaultPassword property is set to an empty string ("").

For related information, see the topics "DefaultUser Property" and "DefaultPassword Property" in DAO Help.

CDaoWorkspace::SetIniPath

Call this member function to specify the location of Windows registry settings for the Microsoft Jet database engine.

static void PASCAL SetIniPath(LPCTSTR lpszRegistrySubKey);

Parameters

lpszRegistrySubkey
A string containing the name of a Windows registry subkey for the location of Microsoft Jet database engine settings or parameters needed for installable ISAM databases.

Remarks

Call SetIniPath only if you need to specify special settings. For more information, see the topic "IniPath Property" in DAO Help.

Note

Call SetIniPath during application installation, not when the application runs. SetIniPath must be called before you open any workspaces, databases, or recordsets; otherwise, MFC throws an exception.

You can use this mechanism to configure the database engine with user-provided registry settings. The scope of this attribute is limited to your application and can't be changed without restarting your application.

CDaoWorkspace::SetIsolateODBCTrans

Call this member function to set the value of the DAO IsolateODBCTrans property for the workspace.

void SetIsolateODBCTrans(BOOL bIsolateODBCTrans);

Parameters

bIsolateODBCTrans
Pass TRUE if you want to begin isolating ODBC transactions. Pass FALSE if you want to stop isolating ODBC transactions.

Remarks

In some situations, you might need to have multiple simultaneous transactions pending on the same ODBC database. To do this, you need to open a separate workspace for each transaction. Although each workspace can have its own ODBC connection to the database, this slows system performance. Because transaction isolation isn't normally required, ODBC connections from multiple workspace objects opened by the same user are shared by default.

CDaoWorkspace::SetLoginTimeout

Call this member function to set the value of the DAO LoginTimeout property for the workspace.

static void PASCAL SetLoginTimeout(short nSeconds);

Parameters

nSeconds
The number of seconds before an error occurs when you attempt to log in to an ODBC database.

Remarks

When you are attempting to log in to an ODBC database, such as Microsoft SQL Server, the connection may fail as a result of network errors or because the server isn't running. Rather than waiting for the default 20 seconds to connect, you can specify how long the database engine waits before it produces an error. Logging on to the server happens implicitly as part of a number of different events, such as running a query on an external server database. The timeout value is determined by the current setting of the LoginTimeout property.

For related information, see the topic "LoginTimeout Property" in DAO Help.

Chia sẻ qua

CDaoWorkspace Class

Syntax

Members

Public Constructors

Public Methods

Public Data Members

Remarks

Capabilities

Security

Usage

Transactions

Implicit Use of the Default Workspace

Other Operations

Inheritance Hierarchy

Requirements

CDaoWorkspace::Append

Remarks

CDaoWorkspace::BeginTrans

Remarks

CDaoWorkspace::CDaoWorkspace

Remarks

CDaoWorkspace::Close

Remarks

CDaoWorkspace::CommitTrans

Remarks

CDaoWorkspace::CompactDatabase

Parameters

Remarks

CDaoWorkspace::Create

Parameters

Remarks

CDaoWorkspace::GetDatabaseCount

Return Value

Remarks

CDaoWorkspace::GetDatabaseInfo

Parameters

Remarks

CDaoWorkspace::GetIniPath

Return Value

Remarks

CDaoWorkspace::GetIsolateODBCTrans

Return Value

Remarks

CDaoWorkspace::GetLoginTimeout

Return Value

Remarks

CDaoWorkspace::GetName

Return Value

Remarks

CDaoWorkspace::GetUserName

Return Value

Remarks

CDaoWorkspace::GetVersion

Return Value

Remarks

CDaoWorkspace::GetWorkspaceCount

Return Value

Remarks

CDaoWorkspace::GetWorkspaceInfo

Parameters

Remarks

CDaoWorkspace::Idle

Parameters

Remarks

CDaoWorkspace::IsOpen

Return Value

Remarks

CDaoWorkspace::m_pDAOWorkspace

Remarks

CDaoWorkspace::Open

Parameters

Remarks

CDaoWorkspace::RepairDatabase

Parameters

Remarks

CDaoWorkspace::Rollback

Remarks

CDaoWorkspace::SetDefaultPassword

Parameters