Mar 24, 2020 The Auto increment is commonly used to generate primary keys. The defined data type on the Auto increment should be large enough to accommodate many records. Adobe premiere pro cs4 crack. Defining TINYINT as the data type for an auto increment field limits the number of records that can be added to the table to 255 only since any values beyond that would not be accepted. This method is automatically generated but the generated method only includes logic to initialize primary keys to a static value. About this task You may need to ensure that the primary key is a new, unique value.
|
Function | Description |
---|---|
SCOPE_IDENTITY | Returns the last identity value within the current execution scope. SCOPE_IDENTITY is recommended for most scenarios. |
@@IDENTITY | Contains the last identity value generated in any table in the current session. @@IDENTITY can be affected by triggers and may not return the identity value that you expect. |
IDENT_CURRENT | Returns the last identity value generated for a specific table in any session and any scope. |
InsertCommand
is processed, the auto-incremented identity value is returned and placed in the CategoryID column of the current row if you set the UpdatedRowSource property of the insert command to UpdateRowSource.OutputParameters
or to UpdateRowSource.Both
.
UpdatedRowSource
property of the insert command to UpdateRowSource.FirstReturnedRecord
.
GetChanges
method of a DataTable
to create a copy that contains only changed rows, and to use the new copy when calling the Update
method of a DataAdapter
. This is especially useful when you need to marshal the changed rows to a separate component that performs the update. Following the update, the copy can contain new identity values that must then be merged back into the original DataTable
. The new identity values are likely to be different from the original values in the DataTable
. To accomplish the merge, the original values of the AutoIncrement columns in the copy must be preserved, in order to be able to locate and update existing rows in the original DataTable
, rather than appending new rows containing the new identity values. However, by default those original values are lost after a call to the Update
method of a DataAdapter
, because AcceptChanges
is implicitly called for each updated DataRow
.
DataColumn
in a DataRow
during a DataAdapter
update:
AcceptChangesDuringUpdate
property of the DataAdapter
to false
. This affects every DataRow
in the DataTable
being updated. For more information and a code example, see AcceptChangesDuringUpdate.
RowUpdated
event handler of the DataAdapter
to set the Status to SkipCurrentRow. The DataRow
is updated but the original value of each DataColumn
is preserved. This method enables you to preserve the original values for some rows and not for others. Atpl human factors pdf files. For example, your code can preserve the original values for added rows and not for edited or deleted rows by first checking the StatementType and then setting Status to SkipCurrentRow only for rows with a StatementType
of Insert
.
DataRow
during a DataAdapter
update, ADO.NET performs a series of actions to set the current values of the DataRow
to new values returned by output parameters or by the first returned row of a result set, while still preserving the original value in each DataColumn
. First, the AcceptChanges
method of the DataRow
is called to preserve the current values as original values, and then the new values are assigned. Following these actions, DataRows
that had their RowState property set to Added will have their RowState
property set to Modified, which may be unexpected.
UpdateRowSource
enumeration.
UpdateRowSource
enumeration values affect the RowState property of updated rows.
Member name | Description |
---|---|
Both | AcceptChanges is called and both output parameter values and/or the values in the first row of any returned result set are placed in the DataRow being updated. If there are no values to apply, the RowState will be Unchanged. |
FirstReturnedRecord | If a row was returned, AcceptChanges is called and the row is mapped to the changed row in the DataTable , setting the RowState to Modified . If no row is returned, then AcceptChanges is not called and the RowState remains Added . |
None | Any returned parameters or rows are ignored. There is no call to AcceptChanges and the RowState remains Added . |
OutputParameters | AcceptChanges is called and any output parameters are mapped to the changed row in the DataTable , setting the RowState to Modified . If there are no output parameters, the RowState will be Unchanged . |
DataTable
and using a SqlDataAdapter to update the data source and retrieve a new identity column value. The InsertCommand executes two Transact-SQL statements; the first one is the INSERT statement, and the second one is a SELECT statement that uses the SCOPE_IDENTITY function to retrieve the identity value.
UpdatedRowSource
property of the insert command is set to UpdateRowSource.FirstReturnedRow
and the MissingSchemaAction property of the DataAdapter
is set to MissingSchemaAction.AddWithKey
. The DataTable
is filled and the code adds a new row to the DataTable
. The changed rows are then extracted into a new DataTable
, which is passed to the DataAdapter
, which then updates the server.
OnRowUpdated
event handler checks the StatementType of the SqlRowUpdatedEventArgs to determine if the row is an insert. If it is, then the Status property is set to SkipCurrentRow. The row is updated, but the original values in the row are preserved. In the main body of the procedure, the Merge method is called to merge the new identity value into the original DataTable
, and finally AcceptChanges
is called.
Autonumber
values from a Jet 4.0 database. The Jet database engine does not support the execution of multiple statements in a batch or the use of output parameters, so it is not possible to use either of these techniques to return the new Autonumber
value assigned to an inserted row. However, you can add code to the RowUpdated
event handler that executes a separate SELECT @@IDENTITY statement to retrieve the new Autonumber
value.
MissingSchemaAction.AddWithKey
, this example configures a DataTable
with the correct schema prior to calling the OleDbDataAdapter to fill the DataTable
. In this case, the CategoryID column is configured to decrement the value assigned each inserted row starting from zero, by setting AutoIncrement to true
, AutoIncrementSeed to 0, and AutoIncrementStep to -1. The code then adds two new rows and uses GetChanges
to add the changed rows to a new DataTable
that is passed to the Update
method.
RowUpdated
event handler uses the same open OleDbConnection as the Update
statement of the OleDbDataAdapter
. It checks the StatementType
of the OleDbRowUpdatedEventArgs for inserted rows. For each inserted row a new OleDbCommand is created to execute the SELECT @@IDENTITY statement on the connection, returning the new Autonumber
value, which is placed in the CategoryID column of the DataRow
. The Status
property is then set to UpdateStatus.SkipCurrentRow
to suppress the hidden call to AcceptChanges
. In the main body of the procedure, the Merge
method is called to merge the two DataTable
objects, and finally AcceptChanges
is called.
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