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标题: 怎样用ADO打开一个带密码的Access库？ [打印本页]

作者: 韩冰 时间: 2005-1-26 12:38
标题: 怎样用ADO打开一个带密码的Access库？
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> 
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>Creates a new Recordset object and appends it to the Recordsets collection. 
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> 
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>Syntax 
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> 
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>For Connection and Database objects: 
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> 
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>Set recordset = object.OpenRecordset (source, type, options, lockedits) 
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> 
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>For QueryDef, Recordset, and TableDef objects: 
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> 
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>Set recordset = object.OpenRecordset (type, options, lockedits) 
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> 
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>The OpenRecordset method syntax has these parts. 
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> 
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art Description 
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>recordset An object variable that represents the Recordset object you wantt to 
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>open. 
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>object An object variable that represents an existing object from which you 
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>want to create the new Recordset. 
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>source A String specifying the source of the records for the new Recordset. 
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>The source can be a table name, a query name, or an SQL statement that 
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>returns records. For table-type Recordset objects in Microsoft Jet databases, 
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>the source can only be a table name. 
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>type Optional. A constant that indicates the type of Recordset to open, as 
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>specified in Settings. 
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>options Optional. A combination of constants that specify characteristics of 
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>the new Recordset, as listed in Settings. 
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>lockedits Optional. A constant that determines the locking for the Recordsset, 
as specified in Settings. 
Settings 
 
You can use one of the following constants for the type argument. 
 
Constant Description 
 
 
dbOpenTable Opens a table-type Recordset object (Microsoft Jet workspaces 
only). 
dbOpenDynamic Opens a dynamic-type Recordset object, which is similar to an 
ODBC dynamic cursor. (ODBCDirect workspaces only) 
dbOpenDynaset Opens a dynaset-type Recordset object, which is similar to an 
ODBC keyset cursor. 
dbOpenSnapshot Opens a snapshot-type Recordset object, which is similar to an 
ODBC static cursor. 
dbOpenForwardOnly?Opens a forward-only-type Recordset object. 
Note If you open a Recordset in a Microsoft Jet workspace and you don't 
specify a type, OpenRecordset creates a table-type Recordset, if possible. If 
you specify a linked table or query, OpenRecordset creates a dynaset-type 
Recordset. In an ODBCDirect workspace, the default setting is dbOpenForwardOnl 
y. 
 
You can use a combination of the following constants for the options 
argument. 
 
Constant Description 
dbAppendOnly?Allows users to append new records to the Recordset, but 
prevents them from editing or deleting existing records (Microsoft Jet 
dynaset-type Recordset only). 
dbSQLPassThrough?Passes an SQL statement to a Microsoft Jet-connected ODBC 
data source for processing (Microsoft Jet snapshot-type Recordset only). 
dbSeeChanges Generates a run-time error if one user is changing data that 
another user is editing (Microsoft Jet dynaset-type Recordset only). This is 
useful in applications where multiple users have simultaneous read/write 
access to the same data. 
dbDenyWrite?Prevents other users from modifying or adding records (Microsoft 
Jet Recordset objects only). 
dbDenyRead?Prevents other users from reading data in a table (Microsoft Jet 
table-type Recordset only). 
dbForwardOnly?Creates a forward-only Recordset (Microsoft Jet snapshot-type 
Recordset only). It is provided only for backward compatibility, and you 
should use the dbOpenForwardOnly constant in the type argument instead of 
using this option. 
dbReadOnly?Prevents users from making changes to the Recordset (Microsoft Jet 
only). The dbReadOnly constant in the lockedits argument replaces this 
option, which is provided only for backward compatibility. 
dbRunAsync Runs an asynchronous query (ODBCDirect workspaces only). 
dbExecDirect?Runs a query by skipping SQLPrepare and directly calling 
SQLExecDirect (ODBCDirect workspaces only). Use this option only when you抮e 
not opening a Recordset based on a parameter query. For more information, see 
the "Microsoft ODBC 3.0 Programmer抯 Reference." 
dbInconsistent?Allows inconsistent updates (Microsoft Jet dynaset-type and 
snapshot-type Recordset objects only). 
dbConsistent?Allows only consistent updates (Microsoft Jet dynaset-type and 
snapshot-type Recordset objects only). 
Note The constants dbConsistent and dbInconsistent are mutually exclusive, 
and using both causes an error. Supplying a lockedits argument when options 
uses the dbReadOnly constant also causes an error. 
 
You can use the following constants for the lockedits argument. 
 
Constant Description 
dbReadOnly Prevents users from making changes to the Recordset (default for 
ODBCDirect workspaces). You can use dbReadOnly in either the options argument 
or the lockedits argument, but not both. If you use it for both arguments, a 
run-time error occurs. 
dbPessimistic?Uses pessimistic locking to determine how changes are made to 
the Recordset in a multiuser environment. The page containing the record 
you're editing is locked as soon as you use the Edit method (default for 
Microsoft Jet workspaces). 
dbOptimistic?Uses optimistic locking to determine how changes are made to the 
Recordset in a multiuser environment. The page containing the record is not 
locked until the Update method is executed. 
dbOptimisticValue?Uses optimistic concurrency based on row values (ODBCDirect 
workspaces only). 
dbOptimisticBatch?Enables batch optimistic updating (ODBCDirect workspaces 
only). 
Remarks 
 
In a Microsoft Jet workspace, if object refers to a QueryDef object, or a 
dynaset- or snapshot-type Recordset, or if source refers to an SQL statement 
or a TableDef that represents a linked table, you can't use dbOpenTable for 
the type argument; if you do, a run-time error occurs. If you want to use an 
SQL pass-through query on a linked table in a Microsoft Jet-connected ODBC 
data source, you must first set the Connect property of the linked table's 
database to a valid ODBC connection string. If you only need to make a single 
pass through a Recordset opened from a Microsoft Jet-connected ODBC data 
source, you can improve performance by using dbOpenForwardOnly for the type 
argument. 
 
If object refers to a dynaset- or snapshot-type Recordset, the new Recordset 
is of the same type object. If object 
 refers to a table-type Recordset object, the type of the new object is a 
dynaset-type Recordset. You can't open new Recordset objects from forward-only 
杢ype or ODBCDirect Recordset objects. 
In an ODBCDirect workspace, you can open a Recordset containing more than one 
select query in the source argument, such as 
 
"SELECT LastName, FirstName FROM Authors 
WHERE LastName = 'Smith'; 
SELECT Title, ISBN FROM Titles 
WHERE ISBN Like '1-55615-*'" 
 
The returned Recordset will open with the results of the first query. To 
obtain the result sets of records from subsequent queries, use the 
NextRecordset method. 
 
Note You can send DAO queries to a variety of different database servers 
with ODBCDirect, and different servers will recognize slightly different 
dialects of SQL. Therefore, context-sensitive Help is no longer provided for 
Microsoft Jet SQL, although online Help for Microsoft Jet SQL is still 
included through the Help menu. Be sure to check the appropriate reference 
documentation for the SQL dialect of your database server when using either 
ODBCDirect connections or pass-through queries in Microsoft Jet-connected 
client/server applications. 
 
Use the dbSeeChanges constant in a Microsoft Jet workspace if you want to 
trap changes while two or more users are editing or deleting the same record. 
For example, if two users start editing the same record, the first user to 
execute the Update method succeeds. When the second user invokes the Update 
method, a run-time error occurs. Similarly, if the second user tries to use 
the Delete method to delete the record, and the first user has already 
changed it, a run-time error occurs. 
 
Typically, if the user gets this error while updating a record, your code 
should refresh the contents of the fields and retrieve the newly modified 
values. If the error occurs while deleting a record, your code could display 
the new record data to the user and a message indicating that the data has 
recently changed. At this point, your code can request a confirmation that 
the user still wants to delete the record. 
 
You should also use the dbSeeChanges constant if you open a Recordset in a 
Microsoft Jet-connected ODBC workspace against a Microsoft SQL Server 6.0 (or 
later) table that has an IDENTITY column, otherwise an error may result. 
 
In an ODBCDirect workspace, you can execute asynchronous queries by setting 
the dbRunAsync constant in the options argument. This allows your application 
to continue processing other statements while the query runs in the 
background. But, you cannot access the Recordset data until the query has 
completed. To determine whether the query has finished executing, check the 
StillExecuting property of the new Recordset. If the query takes longer to 
complete than you anticipated, you can terminate execution of the query with 
the Cancel method. 
 
Opening more than one Recordset on an ODBC data source may fail because the 
connection is busy with a prior 
OpenRecordset call. One way around this is to use a server-side cursor and 
ODBCDirect, if the server supports this. Another solution is to fully 
populate the Recordset by using the MoveLast method as soon as the Recordset 
is opened. 
 
If you open a Connection object with DefaultCursorDriver set to 
dbUseClientBatchCursor, you can open a Recordset to cache changes to the data 
(known as batch updating) in an ODBCDirect workspace. Include dbOptimisticBatc 
h in the lockedits argument to enable update caching. See the Update method 
topic for details about how to write changes to disk immediately, or to cache 
changes and write them to disk as a batch. 
 
Closing a Recordset with the Close method automatically deletes it from the 

Recordsets collection. 
 
Note If source refers to an SQL statement composed of a string concatenated 
with a non-integer value, and the system parameters specify a non-U.S. 
decimal character such as a comma (for example, strSQL = "PRICE > " & 
lngPrice, and lngPrice = 125,50), an error occurs when you try to open the 
Recordset. This is because during concatenation, the number will be converted 
to a string using your system's default decimal character, and SQL only 
accepts U.S. decimal characters.

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