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To define a new non-array type means associating with the type name a
procedure for converting from a PostgreSQL string representation to a Scheme
object (the objectifier), a procedure to do the conversion in the
opposite direction (the stringifier), and a default string to use if
none is specified (for example, during an INSERT
operation). For this,
use the define-db-col-type
procedure.
Register type name with default, stringifier and
objectifier procs. name is a symbol. default is a
string to use if the Scheme object is #f
. stringifier is a
proc that takes a Scheme object and returns a string suitable for use in an
INSERT VALUES
SQL command. objectifier is a proc that takes a
string and returns the Scheme object parsed out of it.
Both stringifier and objectifier need not worry about SQL-style quoting (using single quotes) and related quote escaping.
If name already exists, it is redefined.
See also dbcoltype-lookup
.
To express conversion of arrays (no matter the dimensionality) of non-array
types, use the define-db-col-type-array-variant
procedure.
Register type composed, an array variant of simple, with
optional procs. simple should be a type name already
registered using define-db-col-type
. composed is
conventionally formed by appending simple with one or more pairs of
‘[]’ (square braces), with the number of pairs indicating the array
dimensionality. For example, if simple is text
, a
two-dimensional text array would be named text[][]
.
Optional arg procs is a list specifying alternative stringifier and
objectifier procedures (in that order). If unspecified, simple is
looked up and its stringifier and objectifier are used. See
dbcoltype-lookup
.
The default value of all array types is ‘{}’ and cannot be changed.
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