Data Types

Felis provides an internal type system that is used to define the data types of columns in a schema. These data types are mapped to the appropriate SQL types when instantiating a database and the corresponding VOTable data types when writing information to TAP_SCHEMA.

The following values are supported by the datatype field of a column object:

Type	Description	Notes
boolean	boolean value
byte	8-bit signed integer	See footnote [1]
short	16-bit signed integer
int	32-bit signed integer
long	64-bit signed integer
float	32-bit floating point number	IEEE 745 single precision floating point number
double	64-bit floating point number	IEEE 745 double precision floating point number
char	fixed-length character string
string	variable-length character string
unicode	variable-length Unicode string	Usage of this type is discouraged as it maps to the obsolete UCS-2 encoding in VOTable, and is not usable for UTF-8 strings.
text	variable-length text string
binary	variable-length binary blob
timestamp	timestamp value

[1] (1,2)

The Felis type byte currently maps to signed 8-bit integral types in the supported database back ends. VOTable, and therefore TAP_SCHEMA, only has an unsigned 8-bit type. The Felis mapping is under review at this time; in the mean time, if you are intentionally storing signed byte values in a database with a Felis-derived schema, we recommend the use of a VOTable type override in Felis, votable:datatype: short, to ensure that the signedness of the values is preserved in TAP output.

Data Type Mappings

Felis types are mapped to SQL types when creating a schema in a database and VOTable primitives when writing information to TAP_SCHEMA. The following table shows these mapping:

Felis	SQLite [2]	MySQL	PostgreSQL	VOTable
boolean	BOOLEAN	BOOLEAN	BOOLEAN	boolean
byte [1]	TINYINT	TINYINT	SMALLINT	unsignedByte
short	SMALLINT	SMALLINT	SMALLINT	short
int	INTEGER	INTEGER	INTEGER	int
long	BIGINT	BIGINT	BIGINT	long
float	FLOAT	FLOAT	FLOAT	float
double	DOUBLE	DOUBLE	DOUBLE PRECISION	double
char	CHAR	CHAR	CHAR	char
string	VARCHAR	VARCHAR	VARCHAR	char
unicode	NVARCHAR	NVARCHAR	VARCHAR	unicodeChar
text	TEXT	LONGTEXT	TEXT	char
binary	BLOB	LONGBLOB	BYTEA	unsignedByte
timestamp	TIMESTAMP	DATETIME	TIMESTAMP	char

[2]

SQLite data types use storage classes. The types listed here represent the emitted SQL type for the given Felis type in SQLAlchemy rather than the storage class and are also indicative of the generic SQL type that is emitted when no database dialect is specified.