Add NoneType for (de)serializing None options for other schematypes

[mrijken]

In my apps, I have Colander schemas with optional fields for which None is needed to store the absence of a value in ie a SQL database. For that, the colander.null value can not be used. So I made a supertype which can embrace every other schematype to add the posibility to add None as value.

Example:

typ = NoneType(Boolean())
serialize True --> 'true'
serialize None --> ''
deserialize '' --> None
deserlialize 'true' --> True

[claytron]

Can you update the sphinx docs with more information about this new feature?

[mrijken]

I have added some documentation.

[romanlevin]

@mrijken, you've just saved me a couple of hours of having to implement this myself.

[iksteen]

Any updates on this pull request? I'm looking into migrating one of our projects to use colander 1.0b1, but I need some integers to have an optional None value. I'd rather update the schemas than update all the views.

[tseaver]

Should that read "cannot be used for strings"?

[mrijken]

You're right. I should read it twice before committing.

2013/10/16 Tres Seaver notifications@github.com

In docs/null.rst:

• assert deserialized['age'] == None

• deserialized = schema.deserialize({'name':'Fred', 'age': '19'})
• assert deserialized['age'] == 19

• serialized = schema.serialize({'name':'Fred', 'age': None})
• assert serialized['age'] == ''

• serialized = schema.serialize({'name':'Fred', 'age': 19})
• assert serialized['age'] == '19'

+When you use colander.NoneType you can pass the results of the deserialization directly to a database,
+without converting colander.null to None outside the schema. In other words, you have defined in the
+schema that the node can have None as value.
+
+Note: NoneType can be used for strings, because the machinery does not known whether a serialization of "" is

Should that read "cannot be used for strings"?

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[sq9mev]

Any news about this pull request? This seems very useful for me…

[mmerickel]

For some reason SchemaType is not actually a public API, so it probably shouldn't be mentioned here.

[mmerickel]

Basically every type is supposed to handle colander.null, so I think you'll want to take care of that. I'm not a fan of handling the empty string as None in this implementation. I guess you're trying to keep it symmetric in colander's silly I-only-serialize-to-strings sort of way right now. I'd expect to see something closer to if cstruct is colander.null or cstruct is None: return None and no other special cases.

[tseaver]

Thank you for the patch. Can you please:

• Merge with master (or rebase) to allow us to review / merge your changes cleanly.
• Add an entry to CHANGES.rst.
• Add your name to CONTRIBUTORS.txt.

[delijati]

updated in #258