Grade Force Version Not Work at Higher Level - gradle

Question

I use below config to force using old version of library_common in project my_library
my_library
dependencies{
compile("library_A")
compile("library_B")
compile("library_common:old_version"){
force = true
}
}
Library_common is resolved to old_version, which match our expectation
dependency tree
+---library_A
| +---library_common: new_version -> old_version
+---library_B
| +---library_common: old_version
+---library_common: old_version
Another Project my_application then have dependencies on my_library and a non_related_lib
my_application
dependencies{
compile("my_library")
compile("non_related_lib"){transitive = false}
}
Library_common is somehow resolved to new_version which causes the conflicts in my_library.
dependency tree
+---my_library
| +---library_A
| | +---library_common: new_version
| \---library_B
| | +---library_common: old_version -> new_version
| \---library_common: old_version -> new_version
+---non_related_lib
I know I can force library_common version again in my_application, but it seems not right, as my_library should handle this conflict by itself.
It seems to me Gradle ignores force=true constraint declared in a direct dependency. Could somebody help explain if this is the way Gradle works?
Also, another thought is to exclude library_common in library_A and library_B. Will need to test it. But this way may become complicated when library_common is included as a transitive dependency of library_A/B, and nested level is deep.
Could someone provide any suggestions on the best practice to downgrade a dependency in a library project?
Thank you!!

Answer 1

If you want to force an older version of a transitive dependency, you should use dependency constraints. If your libraries are all published using Gradle, the constraints are also packaged within the Gradle module metadata, which means they will be preserved whenever you add your libraries as dependencies to some other project.
This all means, your buildscript has to change to something like this:
// my_library
dependencies{
compile("library_A") // do not specify a version of library_A here
constraints {
compile("library_A:version") // specify a version of library_A here
compile("library_common") { // do not specify a version of library_common here
version {
strictly(old_version) // specify a version of library_common here
}
}
}
compile("library_B")
}