tailieunhanh - SQL Anywhere Studio 9- P5

Tham khảo tài liệu 'sql anywhere studio 9- p5', công nghệ thông tin, cơ sở dữ liệu phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 236 Chapter 7 Synchronizing Tip If you don t want a particular type of operation to be applied to the consolidated database just leave that script out. For example if you want inserts and updates to be applied but not deletes leave out the upload_delete script. The deletes will still be uploaded but they will be ignored by the MobiLink server. Handling Upload Conflicts In general an upload conflict is anything that causes a resolve_conflict event to occur for a single uploaded row. This definition is vague for a reason An upload conflict isn t just a problem to be dealt with it is a powerful programming tool. Upload conflicts come in two flavors natural conflicts and forced conflicts and a forced conflict can be anything you want it to be. This section will discuss natural conflicts first then forced conflicts. A natural conflict is caused by the same row being updated on different remote databases and then uploaded to the consolidated database. It can also occur if the same row is updated on the consolidated database and on a remote database and then that row is uploaded from the remote database to the consolidated. Some applications don t have conflicts the databases are set up so it s impossible for the same row to be updated on more than one database. Other applications don t care the default action of last uploaded update wins is okay. But many applications have special business-related rules that must be followed when a conflict occurs. For these applications the conflicts must first be detected and then dealt with and each of those actions require more MobiLink scripts to be written. Every uploaded update consists of two copies of the row the old column values as they existed on the remote database before the row was updated and the new column values that the upload_update script would normally apply to the consolidated database. A natural conflict is detected by comparing the old values being uploaded not with the new values but with the values as .