This document describes how CQL types are mapped to and from Lua in UDF.
When converting to Lua, these types are mapped to Lua strings.
When converting to CQL, types that Lua coerces to string are accepted. The values are verified to be valid ASCII or UTF8 as appropriate.
Lua strings can hold arbitrary data, so blobs are converted to and from Lua strings.
Lua 5.3 has native support for 64 bit integers, so all these types are converted to a native integer.
When converting to CQL, types that Lua coerces to integers are supported. If the value is too large for the CQL type, it wraps.
This maps exactly to and from a Lua boolean.
Since UDF are pure functions, a counter is mapped to and from a native integer.
When converting to Lua, these are mapped o Lua’s native double.
When converting to CQL, a number is rounded to a float or double value as appropriate. For example, it is valid to return a integer that is too large to have an exact representation as a double.
These are mapped to a userdata since there is no native support for large numbers is Lua. We try to provide type coercions similar to those Lua has. For example, a UDF returning the CQL type bigint, can return the value 42 with Lua code that returns
The integer 42
The double 42
The string “42”
The varint 42
The decimal 42
When converting to Lua, a date is mapped to the number of days since epoch + 2^31.
When converting to CQL, we support:
integer (number of days since epoch + 2^31).
CQL date literal in a string.
A lua “date table”, but with only year, month and day
When converting to Lua we produce the table { months = v1, days = v2, nanoseconds = v3 }.
When converting to CQL we support a table in the same format or a CQL duration literal in a string.
This is converted to and from a string (“127.0.0.1” or “::1”).
When converting to Lua we pass an integer with the number of seconds since midnight.
When converting to CQL we support an integer with the same meaning or a CQL time literal in a string.
When converting to Lua we pass an integer with the number of milliseconds since the epoch.
When converting to CQL we support integers with the same meaning or CQL timestamp literal in a string.
These are converted to and from the string representation.
A list is represented as a sequence in lua. A list with “foo” and “bar” is represented as {“foo”, “bar”}. It is an error to return a table that is not a sequence.
A tuple is represented the same way as a list, but on return we check the number of elements and the types.
These are converted to and from lua tables. A map from “foo” to 42 is represented as {foo = 42}.
A UDT is represented by a table like a map, but on return we check that:
There are no unexpected keys
All expected keys are present
The fields have valid types
A set is represented in lua by the keys of a table. A set with 1, 2 and 3 is represented by as {[1] = true, [2] = true, [3] = true}. On return the values are checked to be true.
Note that, like every other Lua table, the set is underscored. It is sorted when converting back to CQL.