Add collection element types

[andrykonchin]

Updates:

• extended supported types list of :of option in field declaration for set field
• add :of option for array field

of option now supports all scalar types (except boolean) like integer, number, date, datetime, serializable and custom types.

Example:

field :values, :set, of: :datetime

Some type declarations have options like store_as_string or serializer. It's possible to specify them for elements type:

field :values, :array, of: { serialized: { serializer: JSON } }

Related Issue #272

[pboling]

Left some comments on documentation. Haven't reviewed the rest yet.

[pboling]

I do not understand this statement:

It's possible to specify them for elements type:

Does it mean this,

It's possible to specify a type declaration for each field:

[andrykonchin]

@pboling Hm, no.

I meant user can declare usual field options when declares set elements type e.g. set of datetime and store datetime in numeric or string format.

[pboling]

I'm not sure how to improve it then. I still don't fully understand. Maybe add a few more fields to complete the example?

[pboling]

Improving grammar for clarity:

DynamoDB doesn't allow empty strings in fields configured as set.
Abiding by this restriction, when Dynamoid saves a document it removes all empty strings in set fields.

[pboling]

Is there any guidance we can add relative to why or when one should use a set and when one should use an array, aside from the element type restrictions? This may not be the right place for that sort of thing.

[andrykonchin]

@pboling

The guidance could be found in DynamoDB's documentation as far as Dynamoid's types are mapped straightforward to DynamoDB's - array on List and set on Set.

[pboling]

As far as I can tell, the mapping you refer to is not in the README anywhere. Might be in some wiki, but it would be helpful to clarify in the README. Most Rubyists are not familiar with Ruby's Set class:

Amazon DynamoBD	Dynamoid gem
List	Array
Set	Set

[andrykonchin]

@pboling Updated Readme. Please check new wording.

[andrykonchin]

@pboling ping

Did you have a chance to look at new wording here? Have I missed anything?

[pboling]

@andrykonchin The latest documentation looks great!