18. Bigloo A practical Scheme compiler User manual for version 4.0a January 2013 -- Database

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top: | Bigloo A practical Scheme compiler User manual for version 4.0a January 2013

Database

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Bigloo supports database programming. The current version proposes a SQLite binding.

### 18.1 SQLite

The Bigloo's C back-end supports SQL queries. It relies on the SQLite library (http://www.sqlite.org/). The SQLite binding is accessible to Bigloo via the `sqlite` library. Here is an example of module that uses this library.

    (module example1
      (library sqlite))

    (let ((db (instantiate::sqlite)))
      ...)

sqlite | Bigloo Sqlite class

    (class sqlite
       (path::bstring read-only (default ":memory:")))

The instances of the class `sqlite` hold SQLite databases. A database may be permanently stored on a disk or loaded in memory. The class attribute `path` is the location on the disk where the database is stored. The special path `:memory:` denotes in-memory databases. When an instance is created a SQLite database is opened.
Example:

    (define db1 (instantiate::sqlite (path "/tmp/foo.db")))
    (define db2 (instantiate::sqlite))

Binds the global variable `db1` to a database that is stored on the file system at location `/tmp/foo.db`. This example also binds the global variable `db2` to an in-memory SQLite database.

sqlite-close `sqlite` | Bigloo Sqlite function

This function closes a database previously opened by creating an instance of the class `sqlite`.
Example:

    (let ((db (instantiate::sqlite)))
      (sqlite-exec db "CREATE TABLE table1 (x INTEGER, y INTEGER)")
      (sqlite-exec db "INSERT INTO table1 VALUES( ~a, ~a )" 1 4)
      (sqlite-close db))

sqlite-format `string` `arg` ... | Bigloo Sqlite function

Constructs a string of characters representing an SQLite commands. This function acts as `format` (see Input and Output). It is augmented with three additional escape sequence: `~q`, `~k`, and `~l`. The first one build a string of characters where the characters denoting SQL strings (i.e., the character `'`) is automatically escaped. The escape character `~k` introduces a list of SQL strings. The escape character `~l` introduces a SQL list.
Summary of all escape codes:

- `~a` The corresponding value is inserted into the string as if printed with display.
- `~s` The corresponding value is inserted into the string as if printed with write.
- `~%` A newline is inserted.
- `~~` A tilde `~` is inserted.
- `~q` An SQL escaped string.
- `~l` Introduces a list (comma separated).
- `~k` Introduces a list of SQL strings.

Examples:

    (module example
       (library sqlite))

    (sqlite-format "~a" "foo'bar") => "foo'bar"
    (sqlite-format "~q" "foo'bar") => "'foo''bar'"
    (sqlite-format "~a" '("foo'bar" "foo")) => "(foo'bar foo)"
    (sqlite-format "~k" '("foo'bar" "foo")) => "'foo''bar','foo'"
    (sqlite-format "~l" '("foo'bar" "foo")) => "foo'bar,foo"

sqlite-exec `sqlite` `string` `arg` ... | Bigloo Sqlite function

The function `sqlite-exec` executes an SQLite command. The command is the built by implicitly invoking `sqlite-format` on `string` and the optional `arg` arguments. This function returns a single element, the first one returned by the SQL engine.
Example:

    (module example
       (library sqlite))

    (define *db* (instantiate::sqlite))

    (sqlite-exec *db* "CREATE TABLE foo (x INTEGER, y INTEGER)")
    (for-each (lambda (x)
    		(sqlite-exec *db*  "INSERT INTO foo VALUES(~A, ~A)" x (* x x)))
    	     (iota 10))
    (sqlite-exec *db* "SELECT * FROM foo")
       => 9

sqlite-eval `sqlite` `procedure` `string` `arg` ... | Bigloo Sqlite function

The function `sqlite-eval` invokes a SQLite command built by implicitly invoking `sqlite-format` on `string` and the optional `arg` arguments. The result of the function is built by applying `procedure` to the first value returned by the SQLite call.
Note: user callback (`procedure`) must not exit. That is they must not invoke a function create by `bind-exit`. Exiting from a callback will leave the database in a inconsistent state that prevent transactions to be rolled back.

sqlite-map `sqlite` `procedure` `string` `arg` ... | Bigloo Sqlite function

The function `sqlite-map` invokes a SQLite command built by implicitly invoking `sqlite-format` on `string` and the optional `arg` arguments. The result is a list whose elements are built by applying `procedure` to all the values returned by the SQLite call.
Note: user callback (`procedure`) must not exit. That is they must not invoke a function create by `bind-exit`. Exiting from a callback will leave the database in a inconsistent state that prevent transactions to be rolled back. Example:

    (module example
       (library sqlite))

    (define *db* (instantiate::sqlite))

    (sqlite-exec *db* "CREATE TABLE foo (x INTEGER, y INTEGER)")
    (for-each (lambda (x)
    		(sqlite-exec *db*  "INSERT INTO foo VALUES(~A, ~A)" x (* x x)))
    	     (iota 10))
    (sqlite-map *db*
      (lambda (s1 s2) (+ (string->integer s1) (string->integer s2)))
      "SELECT * FROM foo")
       => (0 2 6 12 20 30 42 56 72 90)

Example2:

    (module example
       (library sqlite))

    (define *db* (instantiate::sqlite))

    (sqlite-exec *db* "CREATE TABLE foo (x INTEGER, y INTEGER)")
    (for-each (lambda (x)
    		(sqlite-exec *db*  "INSERT INTO foo VALUES(~A, ~A)" x (* x x)))
    	     (iota 10))
    (sqlite-map *db* vector "SELECT * FROM foo")
       => '(#("0" "0")
    	#("1" "1")
    	#("2" "4")
    	#("3" "9")
    	#("4" "16")
    	#("5" "25")
    	#("6" "36")
    	#("7" "49")
    	#("8" "64")
    	#("9" "81"))

sqlite-name-of-tables `sqlite` | Bigloo Sqlite function

Returns the name of tables in the database. This list can also be obtained with

    (sqlite-map db
       (lambda (x) x)
       "SELECT name FROM sqlite_master WHERE type='table'")

sqlite-last-insert-rowid `sqlite` | Bigloo Sqlite function

Returns the SQLite rowid of the last inserted row.

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Last update Thu Jan 24 17:08:36 2013.