New feature: faster fixture loading via loaddata command

[JorisBenschop]

As per ​this forum discussion, I have created a patch to improve load times for the loaddata command under some circumstances.

Currently the “loaddata” management command uses the obj.save() method for each deserialized object within a fixture. This function first tries an UPDATE statement and, if that fails, tries an INSERT statement.

I propose to add two optional flags to the loaddata command:

–force-insert adds the “force_insert=True” to the save() method. This reduces load time by ~50% but has an increased risk of the upload failing in case the record already exists.

–bulk_create: This option groups records in the fixture by the model, and insert the group as a single bulk_create statement. For large fixtures, I have achieved a 1000-fold improvement in loading time. It has a number of risks (already described in the bulk_create section), notably that it skips some routines covered in the save() method of the model.

Both these flags are supposed to be run by people who know that above-mentioned issues will not be a problem for them, and should not be enabled by default.

[Sarah Boyce]

Duplicate of #35904