More complex inheritance in YAML?
Solution 1:
Unfortunately, you can't get the kind of "inheritance" you want to achieve because YAML's "inheritance" is more like a form of "merging hashes".
Expanding out your configuration at the point you use the *default
alias, you have:
foo_database:
server:
ip: 192.168.1.5
port: 2000
db_name: test
user:
name: root
password: root
If you use hashes with the same keys afterwards, they will completely overwrite the hashes declared earlier, leaving you with (excuse the formatting):
foo_database:
server:
ip: 192.168.1.5
port: 2000
db_name: test
user:
name: root
password: root
server:
port: 2001
db_name: foo
user:
password: foo_root
So, in your case, it would seem that since the config is not exactly the same, DRYing up your configuration using anchors and aliases probably isn't the right approach.
More references on this issue below:
- Rake, YAML and Inherited Build Configuration
- Merging hashes in yaml conf files
Edit
If you really wanted to, I think you could reconfigure your YAML as below to get exactly what you want, but in your case, I would say the extra obfuscation isn't worth it:
server_defaults: &server_defaults
ip: 192.168.1.5
port: 2000
user_defaults: &user_defaults
name: root
password: root
database: &default
server:
<<: *server_defaults
db_name: test
user:
<<: *user_defaults
foo_database:
<<: *default
server:
<<: *server_defaults
port: 2001
db_name: foo
user:
<<: *user_defaults
password: foo_root
Solution 2:
How about this? Use multiple anchors.
database: &default
server: &server
ip: 192.168.1.5
port: 2000
db_name: test
user: &user
name: root
password: root
foo_database:
<<: *default
server:
<< : *server
port: 2001
db_name: foo
user:
<< : *user
password: foo_root
It's just a little extra work, and slightly harder to read than if what you wanted were built into YAML as you suggested (I thought it would work that way too). But overall not bad.
Solution 3:
For this sort of problems, I have created a tool: jq-front. By using yq + jq-front, you can achieve it by slightly modifying your input.
in.yaml:
$local:
database_default:
server:
ip: 192.168.1.5
port: 2000
db_name: test
user:
name: root
password: root
# database foo differs from default by only its port and user password
foo_database:
$extends: [ database_default ]
server:
port: 2001
db_name: foo
user:
password: foo_root
And you can process this file by a following command line.
$ yq . -j in.yaml | jq-front | yq . -y
And you will get following output that you wanted.
foo_database:
server:
ip: 192.168.1.5
port: 2001
db_name: foo
user:
name: root
password: foo_root
NOTE: jq-front is very slow. On my machine the command took 2.5s, which did not matter to me too much since system configuration can be read once and only the converted file is used by the rest of my program.
NOTE: If you use docker + bash, it's lot easier to install jq-front by docker. You only need to add following function to your .bashrc
or a file that is sourced by it.
function jq-front() {
docker run --rm -i \
-v /:/var/lib/jf \
-e JF_PATH_BASE="/var/lib/jf" \
-e JF_PATH="${JF_PATH}" \
-e JF_DEBUG=${JF_DEBUG:-disabled} \
-e JF_CWD="$(pwd)" \
dakusui/jq-front:"${JF_DOCKER_TAG:-latest}" "${@}"
}