Feature: Make validate_schema_types aware of Plugins::Serialization

[odigity]

I'm currently using the Serialization plugin to map an array in ruby to a text column as JSON.

I just tried out the validates_schema_types helper, and got an "is not a valid string" error on that column.

Would be convenient if the validates_schema_types would check for the Serialization plugin and skip columns that have been configured with it.

[odigity]

So, I didn't want to rush into forking and submitting a PR because frankly I don't have much experience digging into code and contributing to large projects... but I took a look at the code for the relevant plugins, and I suspect this might be accomplished with a change to line 184 of sequel/plugins/auto_validations.rb, from:

validates_schema_types(keys, opts[:schema_types]) if model.auto_validate_types?

to:

validates_schema_types(class.responds_to?(:serialization_map) ? keys - class.serialization_map.keys : keys, opts[:schema_types]) if model.auto_validate_types?

(I would write it differently, putting the key-building code on it's own line and saving the results to a local variable, but I figured the most conservative approach would be start with the minimal change and go from there.)

BTW - The only reason I got this far was because of how cleanly the code is written, so thanks!

[jeremyevans]

The auto_validations plugin already uses the :from=>:values option to check the underlying values. If you want to use validates_schema_types with the serialization plugin, use the :from=>:values option just as the auto_validations plugin does, so it looks at the serialized value instead of the deserialized value.

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