Here’s how to use rollback() function.
Description:
Roll back a database transaction.
Syntax:
db.rollback (spn)
Note:
The function rolls back the transaction to the specified savepoint. Rollback all transactions when the parameter is omitted.
Parameter:
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db |
Database connection |
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spn |
Savepoint name |
Example:
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A |
B |
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1 |
=create(ID,NAME,GENDER,AGE).record([3, "AAA","F",14]) |
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2 |
=connect@e("demo") |
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Establish a connection and use @e option to automatically control the commit and rollback operations. |
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3 |
=A2.savepoint("s1") |
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set the savepoint named s1. |
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4 |
>A2.execute@k(A1,"update STUDENTS2 set NAME=?,GENDER=?,AGE=? where ID=?",NAME,GENDER,AGE,ID) |
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Execute the sql statement, update table STYDENTS2 according to A1’s records, and use @k option to not to commit the transaction. |
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5 |
=A2.error() |
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Get the error code generated from the execution of the previous SQL statement. |
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6 |
if A5==0 |
>A2.commit() |
Commit if there is not an error. |
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7 |
else |
>A2.rollback("s1") |
Roll back if there is an error. |
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8 |
>A2.close() |
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Close the connection. |
Related function:
Description:
Restore a composite table file to the previous state when update error happens.
Syntax:
f.rollback()
Note:
The function restores a composite table file’s entity table to the previous state when an error happens during adding, deleting, and modifying data.
Note: When error happens at the update of a composite table file, a file error prompt will appear if you use f.open() to open the composite table file. In this case rollback() is needed to do a rollback action. Different from the rollback operation on an ordinary database, there isn’t a special rollback mechanism for composite tables, users need to call f.rollback() function to to do the rollback manually.
Parameter:
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f |
A composite table file or a homo-name files group |
Return value:
Boolean
Example:
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A |
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1 |
=file("D:/ckv.ctx") |
There is an error about ckv.ctx in executing T.update(P:D), so error is reported when f.open() is used: Error about ckv.ctx, call f.rollback() to restore. |
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2 |
=A1.rollback() |
Restore composite table file ckv.ctx to the state before update is performed. |