You can pass an optional callback function to the call to check. This callback gets called for each unresolved dependency in the transaction set. You can use this callback to try to automatically bring in required packages, for example.

The basic syntax for the transaction check callback is:

def checkCallback(ts, TagN, N, EVR, Flags):

# Do something…

You can use a check callback to automatically bring in packages that are required into a transaction set. You can bring in packages from the Red Hat RPM database package, which contains a database of all Red Hat packages, the rpmdb-redhat package. You can open the database from this package by using the trick described previously for opening transactions to more than one RPM database at a time. Simply set the _dbpath macro to "/usr/lib/rpmdb/i386-redhat-linux/redhat", or the location of your rpmdb-redhat database, and create a transaction set. Your check callback can then search this extra database and add packages from that database into the current, real RPM database.

Your check callback can also attempt to find package files to resolve dependencies, from a disk directory or network archive for example. The following code shows a stub check callback that you can fill in to try to resolve dependencies. This callback sets up a format for finding unresolved packages in another RPM database, or elsewhere. You need to fill in the skeleton with the algorithm you want to actually resolve the dependencies.

def checkCallback(ts, TagN, N, EVR, Flags):

if TagN == rpm.RPMTAG_REQUIRENAME:

prev = ""

Nh = None

if N[0] == '/':

dbitag = 'basenames'

else:

dbitag = 'providename'

# What do you need to do.

if EVR:

print "Must find package [", N, "-", EVR, "]"

else:

print "Must find file [", N, "]"

if resolved:

# ts.addIntall(h, h, 'i')

return -1

return 1

Depending on the values passed to the callback, your code must either find a package itself or a package that provides a given file or capability to resolve the dependency. If you have another RPM database to look at, such as the rpmdb-redhat database, you can use dbMatch to find the necessary packages in that database. If, however, you are working with a directory of RPM files, you need to build up file names from the package name, version, and release.