Features suggestion 2

Here are several features I’d like to suggest. after using liquibase for awhile

  1. User friendly messages for failed preconditions.
    I’d like to have a way to specify a message for each precondition, which will be shown to user in case of precondition failure. 
    For example, if I defined a precondition
I'd like to add a message that only Oracle and MySQL are supported, like this
  1. PropertyDefinedPrecondition
    Liquibase allows to use properties in a from ${propertyName}. Properties are defined in command line or somewhere else.
    Undefined property can lead to unexpected behaviour, which is hard to analyse. I’d like to have a way to check that property is actually defined before using it. I think the best way is to define a new precondition check, so the following would be possible:
The failure type specifies the precondition result - failure or error. For now I resolved this problem with implementing custom precondition.
  1. Hooks for GUI.
    I’d like to create some GUI around Liquibase tool and I’d like it to have some progress bar.
    So I need some hooks (or a way to supply observers/listeners) to get the current status of the operation.

  2. Please, include documentation about Liquibase tags into distribution bundle. It is not convinient to read the docs from site, especially via slow connections.

Thanks for the suggestions, they are all good. I created issues for them in http://liquibase.jira.com (http://liquibase.jira.com/browse/CORE-438, CORE-439, CORE-440, CORE-441)

#1 & #2 should be doable for the 2.0 release. 

#3 will probably be later

I have looked into #4, but I wasn’t able to find a good export program for the wiki software.  I will keep looking into it, though.