by Firstname Lastname, Another Person, Third Person
Early Draft
(sql-open database-name . parameters) => database
(sql-close database)
(sql-do database statement)
Execute one SQL statement for its side effects. [TODO: parameters and escaping]
Raise an exception unless the statement is successful.
While sql-do can execute any SQL statement, it's meant for things
like INSERT, UPDATE, and DELETE where the side effect is
important but the return value (if any) is not.
(sql-do/row-id database statement) => integer
Like sql-do but returns the row ID that was affected by
statement. For example, an INSERT statement would return the ID of
the new row. Raise an exception if the row ID is not available.
Row IDs in SQL are an implementation-defined feature which is somewhat brittle in practice. Hence the use of row IDs is an anti-pattern. For the sake of convenience we provide them anyway. Use with caution.
(Implementation note: Each SQLite connection keeps a global row ID value. We set it to 0 before executing the statement. If it stays zero, we raise an exception. Else we return the new row ID. While SQLite does not have an official value to denote an invalid row ID, zero is a de facto standard because SQLite row IDs start counting up from 1 unless you manually set the counter to less than 1. Note that SQLite row IDs can be negative, though only if the row ID counter is manually set to a negative value.)
(sql-get-all database statement [map-row row-accumulator]) => state
Execute one SQL statement like sql-do but also fetch any and all resulting rows.
For each row, call (apply map-row columns). In other words,
map-row gets as many arguments as there are result columns. The
arguments use Scheme datatypes: integer, real, string. SQL blobs
become Scheme bytevectors.
SQL NULL becomes Scheme null for compatibility with
SRFI 180
and with other SQL databases that have more types.
Notably, #t and #f would be the natural values
of a boolean column, making #f unusable as NULL.
Each call to map-row should return one value and the row-accumulator is called with that value. Finally, row-accumulator is tail-called with an end-of-file object. Whatever row-accumulator returns (possibly multiple values) becomes the return value from sql-get-all.
If map-row is not supplied, the default is vector, which turns each
result row into a Scheme vector.
If row-accumulator is not supplied, the default is
list-accumulator from SRFI 158, which collects the rows into a list.
(sql-get-one database statement [map-row]) => values
Like sql-get-all but expects exactly one result row. If there are no rows, or if there is more than row, an exception is raised.
Return the values from tail-calling (apply map-row columns) with the
sole result row, the result. The details are as for sql-get-all.
However, if map-row returns multiple values, all of them are
preserved.
If map-row is not supplied, the default is values which returns
the columns of the row as multiple values. values is a good default
because a query returning a single SQL value returns a single Scheme
value. The Scheme programmer will not have to unpack that value from a
one-element vector or list.
Gambit FFI implementation attached.
This API was inspired by the Bigloo SQLite module.
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