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The following pseudocode provides an overview of the sequence in which download events, and hence the script of the same name, are invoked.
These events take place at the download location in the complete event model provided in Overview of MobiLink events.
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prepare_for_download
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modify_last_download_timestamp
prepare_for_download
if( modify_last_download_timestamp script is defined
or prepare_for_download script is defined ) {
COMMIT
}
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download
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begin_download // Connection event.
for each table being synchronized {
begin_download // Table event.
}
handle_DownloadData
for each table being synchronized {
begin_download_deletes
for each row in download_delete_cursor {
if( all primary key columns are NULL ) {
send TRUNCATE to remote
} else {
send DELETE to remote
}
}
end_download_deletes
begin_download_rows
for each row in download_cursor {
send INSERT ON EXISTING UPDATE to remote
}
end_download_rows
}
modify_next_last_download_timestamp
for each table being synchronized {
if( begin_download table script is called ) {
end_download // Table event
}
}
if( begin_download connect script is called ) {
end_download // Connection event
}
for each table being synchronized {
download_statistics // Table event.
}
download_statistics // Connection event.
COMMIT
If an acknowledgement is expected, and if no confirmation of the downloads is received from the client, the entire download transaction is rolled back in the consolidated database.
For SQL Anywhere remotes, see SendDownloadACK (sa) extended option. For UltraLite remotes, see Send Download Acknowledgment synchronization parameter.
The download stream does not distinguish between inserts and updates. The script associated with the download_cursor event is a SELECT statement that defines the rows to be downloaded. The client detects whether the row exists and carries out the appropriate insert or update operation.
At the end of the download processing, the client automatically deletes rows that violate referential integrity.