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Posted to issues@hop.apache.org by "dsanderbi (via GitHub)" <gi...@apache.org> on 2025/10/06 20:17:05 UTC
[I] [Feature Request]: Default Resolver for Variables (hop)
dsanderbi opened a new issue, #5787:
URL: https://github.com/apache/hop/issues/5787
### What would you like to happen?
It would be very useful to implement a default resolver. This resolver would allow specifying a default value to use in case a variable is not set.
Examples:
- `${my-var}` not set → `#{default-resolver:${my-var}:123}` ⇒ 123
- `${my-var}` set to 0 → `#{default-resolver:${my-var}:123}` ⇒ 0
Default value can itself be a variable:
- `#{default-resolver:${my-var}:${my-var-default}}`
### Issue Priority
Priority: 2
### Issue Component
Component: Hop Config, Component: Other
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Re: [I] [Feature Request]: Default Resolver for Variables (hop)
Posted by "mattcasters (via GitHub)" <gi...@apache.org>.
mattcasters commented on issue #5787:
URL: https://github.com/apache/hop/issues/5787#issuecomment-3664624643
With sufficient integration tests to validate previous functionality we could implement it here: https://github.com/apache/hop/blob/8ff5bd2c2b436b7ea41416c4fb260f4ae4c82780/core/src/main/java/org/apache/hop/core/variables/Variables.java#L165
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Re: [I] [Feature Request]: Default Resolver for Variables (hop)
Posted by "dsanderbi (via GitHub)" <gi...@apache.org>.
dsanderbi commented on issue #5787:
URL: https://github.com/apache/hop/issues/5787#issuecomment-3665038954
If that’s the case, I would suggest NOT using the variable-based approach.
An extension could still be added later if the community deems it necessary
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Re: [I] [Feature Request]: Default Resolver for Variables (hop)
Posted by "dsanderbi (via GitHub)" <gi...@apache.org>.
dsanderbi commented on issue #5787:
URL: https://github.com/apache/hop/issues/5787#issuecomment-3664831777
> Never close the ones with "mixed feelings", they are usually the most interesting. But if we want default values, perhaps we can add another semi-colon option to ALL resolvers in the core functionality? That way you could say something like `#{hashicorp-vault:edw:hostname:localhost}`
If the semi-colon option is the way to go, we should consider to have the default as optional.
It would be annoying for people to always set a default, if they do not want to set one.
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Re: [I] [Feature Request]: Default Resolver for Variables (hop)
Posted by "mattcasters (via GitHub)" <gi...@apache.org>.
mattcasters commented on issue #5787:
URL: https://github.com/apache/hop/issues/5787#issuecomment-3665025556
Having a simple value as the default would probably solve most of the usecases and is simpler. Resolving a variable is more flexible but also requires more work (define another variable).
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Re: [I] [Feature Request]: Default Resolver for Variables (hop)
Posted by "mattcasters (via GitHub)" <gi...@apache.org>.
mattcasters commented on issue #5787:
URL: https://github.com/apache/hop/issues/5787#issuecomment-3664608668
Never close the ones with "mixed feelings", they are usually the most interesting.
But if we want default values, perhaps we can add another semi-colon option to ALL resolvers in the core functionality?
That way you could say something like `#{hashicorp-vault:edw-hostname:localhost}`
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Re: [I] [Feature Request]: Default Resolver for Variables (hop)
Posted by "dsanderbi (via GitHub)" <gi...@apache.org>.
dsanderbi commented on issue #5787:
URL: https://github.com/apache/hop/issues/5787#issuecomment-3664860921
What would be the pros and cons of the two options?
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Re: [I] [Feature Request]: Default Resolver for Variables (hop)
Posted by "dsanderbi (via GitHub)" <gi...@apache.org>.
dsanderbi commented on issue #5787:
URL: https://github.com/apache/hop/issues/5787#issuecomment-3664534985
> So like a parameter. I like the idea but have mixed feelings about the transparency and complexity to implement the parsing algorithm for nested variable expressions. Perhaps `#{default-resolver:VARIABLE_NAME:default}` could be a simple starting point. You could indicate in the resolver if you want to resolve `default` as a variable as well, but I don't know if that makes your projects easier or harder to maintain ;-)
Hi @mattcasters,
Thanks for the input yes, this is a viable approach. I implemented it as follows:
```bash
#{default-resolver:ETL_MODE;default-value:value}
```
Since the value corresponds to a column in the resolver, I need to provide both the default value and the variable that should be evaluated.
<img width="792" height="632" alt="Image" src="https://github.com/user-attachments/assets/1eabf0b2-e47d-435d-b9da-dbcda744df31" />
---
Since you have mixed feelings about the feature request, should we close the ticket?
As the current resolver-pipeline shown above is a workaround that i can use.
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Re: [I] [Feature Request]: Default Resolver for Variables (hop)
Posted by "mattcasters (via GitHub)" <gi...@apache.org>.
mattcasters commented on issue #5787:
URL: https://github.com/apache/hop/issues/5787#issuecomment-3627823083
So like a parameter. I like the idea but have mixed feelings about the transparency and complexity to implement the parsing algorithm for nested variable expressions. Perhaps `#{default-resolver:VARIABLE_NAME:default}` could be a simple starting point. You could indicate in the resolver if you want to resolve `default` as a variable as well, but I don't know if that makes your projects easier or harder to maintain ;-)
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Re: [I] [Feature Request]: Default Resolver for Variables (hop)
Posted by "mattcasters (via GitHub)" <gi...@apache.org>.
mattcasters commented on issue #5787:
URL: https://github.com/apache/hop/issues/5787#issuecomment-3664839318
Of-course optional. It should be easy to detect. Should we go for a default value or a variable to resolve, e.g. `#{hashicorp-vault:edw:hostname-key:VAR_EDW_DEFAULT_HOSTNAME}`?
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