cubicweb #1143504 [transaction] have a precommit() command [in-progress]

available, for instance, in cw shells it would flush all precommit operations but not actually commit() data to the db

use case: an import script that does a lot of fire_transition calls must do a commit() juste after for db state to be coherent; this is (quite slow and even) annoying whenever one must start the script again

pbs. to overcome: all Ops have a precommit & postcommit event, so there is no way to flush the right Ops (whereas one would of course only execute & flush the precommit Ops)

done in<not specified>
closed by<not specified>
patchMake precommit() callable serveral times [rejected]Move the precommit phase in a dedicated method [rejected]