Module DBI::Type
In: lib/dbi/types.rb

Interface to convert SQL result sets to native Ruby types.

Type is used to convert result sets, which differ from bound variables (which generally go in the opposite direction). For those, see DBI::TypeUtil#convert and DBI::TypeUtil#register_conversion.

Type objects have a simple interface: they implement a parse method which takes the result from the DBD and attempts to convert it to the native type. In the event that they do not do this successfully, they are expected to return the object in its original form.

As a result, many of the built-in Type classes fallback to simpler forms: Float falls back to Integer, Integer to Varchar, etc. It‘s questionable at this point if it‘s desirable to do this, but testing has so far proven it a non-issue.

To reiterate, it is *never acceptable* to return nil or some other placeholder when an object will not successfully parse. Return the object handed to you.

Types must also handle nil as a result to parse. In this case, the advisable solution is to just let the nil pass through, as it‘s usually indicative of a SQL NULL result.

DBI::Row handles delegation of these objects as a converter for the results. Typically, the type object is a class inferred from DBI::TypeUtil#type_name_to_module ran against the ColumnInfo field type_name. However, the the dbi_type field can be used in its place to directly associate a Type object with the column in the DBD, and end-users can leverage StatementHandle#bind_coltype to manually tweak this transformation.

As stated before, Type objects are objects. These objects may be Modules or Classes (and typically are), but there is no reason a traditional constructed object with a parse method cannot be returned; in fact, it is used in a few spots to emulate complex types such as PostgreSQL arrays. Look into the dbi_type ColumnInfo field to pass these types around.

Classes and Modules

Class DBI::Type::Boolean
Class DBI::Type::Decimal
Class DBI::Type::Float
Class DBI::Type::Integer
Class DBI::Type::Null
Class DBI::Type::Timestamp
Class DBI::Type::Varchar