Feature Request: constraint_validations to respect default values

[3ynm]

In order to have a single source of truth it would be neat that the constraint_validations extension respected the default values at the time of initialization (or otherwise, validation) of an object.

Currently a validation error is thrown if one does not initialize the default values already set by the database, and the attribute is required.

[jeremyevans]

Currently, you should use allow_nil: true for constraint validations on columns with default values, since in the case where a value isn't provided, you can assume the default value is valid. I think the only issue in that case is when an explicit nil value is provided. If you are using auto_validations, then auto_validations should handle that case. Do you think that would work for your use case?

In terms of actually fixing this, the constraint_validations metadata table doesn't currently support the allow_missing option, and adding it would make backwards compatibility very tricky. However, maybe the constraint_validations plugin could check the schema just as auto_validations does, determine which columns do not allow NULL and have default values, and add the :allow_missing option to constraint validations for those columns. I'll see if that approach will work.

[3ynm]

I could allow nil values and that would work for my current use case. But it's possible that in the future some nil values end up on the field, for instance if someone creates a row manually. So, it's great to see that you are working on it, thanks!

[jeremyevans]

Can you try this patch?:

diff --git a/lib/sequel/plugins/constraint_validations.rb b/lib/sequel/plugins/constraint_validations.rb
index c84179773..08b42fe4b 100644
--- a/lib/sequel/plugins/constraint_validations.rb
+++ b/lib/sequel/plugins/constraint_validations.rb
@@ -125,14 +125,15 @@ module Sequel
             ds = @dataset.with_quote_identifiers(false)
             table_name = ds.literal(ds.first_source_table)
             reflections = {}
-            @constraint_validations = (Sequel.synchronize{hash[table_name]} || []).map{|r| constraint_validation_array(r, reflections)}
+            allow_missing_columns = db_schema.select{|col, sch| sch[:allow_null] == false && nil != sch[:default]}.map(&:first)
+            @constraint_validations = (Sequel.synchronize{hash[table_name]} || []).map{|r| constraint_validation_array(r, reflections, allow_missing_columns)}
             @constraint_validation_reflections = reflections
           end
         end
 
         # Given a specific database constraint validation metadata row hash, transform
         # it in an validation method call array suitable for splatting to send.
-        def constraint_validation_array(r, reflections)
+        def constraint_validation_array(r, reflections, allow_missing_columns=EMPTY_ARRAY)
           opts = {}
           opts[:message] = r[:message] if r[:message]
           opts[:allow_nil] = true if db.typecast_value(:boolean, r[:allow_nil])
@@ -191,11 +192,13 @@ module Sequel
             reflection_opts[:argument] = arg
           end 
 
-          a << column
-          unless opts.empty?
-            a << opts
+          opts[:from] = :values
+          if column.is_a?(Symbol) && allow_missing_columns.include?(column)
+            opts[:allow_missing] = true
           end
 
+          a << column << opts
+
           if column.is_a?(Array) && column.length == 1
             column = column.first
           end

This should fix the issue. I'll do some more testing with it tomorrow, but assuming no problems, I'll probably commit it.

[3ynm]

Wow, that was quick. Yes, that works indeed.