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sql-de-lite is an experimental interface to SQLite 3 for Chicken 4. The API is subject to change.
sql-de-lite has the following advantages and disadvantages over the sqlite3 extension:
- Integrated SQLite3 library
- Prepared statements are cached, finalized and resurrected as needed
- Rollbacks and database closing can proceed even if statements are open
- Alternate high-level API
- Low-level interface
- High-level interface
- Error handling
- Busy handling
- User-defined functions
- About this egg
Starting with sql-de-lite 0.4.0, the SQLite 3 library is included with the egg. It will be automatically built if the system library is missing or too old; otherwise, the system library is used. You can also override the egg's choice of internal or external library.
In most cases, the following will do the right thing:
The goal of this automatic detection is ensure that you can just depend on this extension without requiring a separate library install step from your users.
SQLite 3.7.11 is included in the egg and will be linked in statically if the system library is missing or older than 3.7.11. The built-in library is compiled with FTS3 and FTS4 (full text search) enabled.
Additionally, a copy of the SQLite3 command shell is installed with your Chicken binaries as chicken-sqlite3.
To force the use of the built-in library, pass the sql-de-lite-internal-lib feature to chicken-install. This requires Chicken 4.5.1 or later.
chicken-install -D sql-de-lite-internal-lib sql-de-lite
A SQLite library installed in the default system library location will be used instead of the built-in library, if present and recent enough.
To force the use of an external library, pass the sql-de-lite-external-lib feature to chicken-install. This requires Chicken 4.5.1 or later.
chicken-install -D sql-de-lite-external-lib sql-de-lite
If you force an external library to be used, the build will fail unless the library is present and recent enough not to cause link errors. The extension assumes you know what you doing, and does not enforce a minimum library version. It is probably necessary to use 3.6.x or later, and the latest stable is always recommended.
Non-standard library location
You can point the build process at a library in a non-standard location--for example, under your home directory--by setting CSC_OPTIONS appropriately.
export CSC_OPTIONS="-I$HOME/local/include -L$HOME/local/lib" chicken-install sql-de-lite
Your own built-in library, static
If you want to use your own built-in library, retrieve the egg source, download the SQLite amalgamation zip file or tarball, then extract it into sqlite3/ inside the egg directory.
chicken-install -r sql-de-lite cd sql-de-lite curl -O http://www.sqlite.org/sqlite-amalgamation-3_7_0_1.zip unzip sqlite-amalgamation-3_7_0_1.zip -d sqlite3 chicken-install # build and install the egg
All we really need is shell.c, sqlite3.c, and sqlite3.h from the amalgamation. Autoconf is not used.
Currently, there is no way to override the compilation options to SQLite3 from chicken-install. If you need to do so, edit the sql-de-lite.setup file.
The low-level interface maps closely to the underlying library API. It may be used in tandem with or instead of the high-level API as desired.
Opening the database[procedure] (open-database filename)
Opens filename, a sqlite3 database. If no database exists, one is created transparently. filename may also be one of the following symbols:
- memory: a new database in memory unique to this connection
- temp or temporary: a new temporary database on disk, visible only to this connection
Returns a #<sqlite-database> object.
Closing the database[procedure] (close-database db)
Closes the database connection db.
The prepared statement cache is flushed prior to closing, finalizing all cached statements. Transient statements must be finalized manually, or the close will fail. (The high-level query/exec interface does this for you.)
Note. Prior to 0.5.0, we did finalize transient statements as well, by walking the library's list of open statements before closing. Unfortunately, this included any statements prepared and owned by SQLite itself--for example, when using FTS--resulting in a double finalize and crash.[procedure] (database-closed? db)
Predicate that checks if database db is closed.
Preparing a SQL statement[procedure] (prepare db sql)
Looks up a prepared statement in the statement cache. If not found, it prepares a new statement and caches it, returning the statement. If found, the statement is reset if need be, and returned. An exception is thrown if a statement we pulled from cache is currently running --- in other words, has been stepped at least once and has not yet returned SQLITE_DONE. (NB: warn and reset would also be acceptable behavior.)
Preparing a SQL statement consisting entirely of whitespace or comment is an error as of 0.5.0.
Returns a #<sqlite-statement> object.[procedure] (prepare-transient db sql)
Same as prepare, but bypasses the cache completely. This procedure is subject to removal.
You must be sure to finalize all transient statements prior to closing the database. For a safer option, use sql/transient with query or exec.[parameter] (prepared-cache-size n) [default: 100]
Sets the capacity of the prepared statement cache, in statements.
When the cache reaches capacity and a new statement is prepared, the least recently used statement is finalized and drops off the cache.
This setting takes effect only upon initiating a new connection, and the statement cache is unique per connection.
Set capacity to 0 to disable the cache; this is not recommended. All statements will become effectively transient, and must be finalized manually. Using sql with query and exec will take care of this for you.
Stepping the statement[procedure] (step statement)
Steps statement and returns one of the following:
- 'row: a row was returned (SQLITE_ROW)
- 'done: the statement is done executing (SQLITE_DONE)
- #f: step failed due to error
#f is only ever returned if raising exceptions is disabled. Completion of execution is still considered a "success" and so the true value 'done is returned, rather than #f.
Upon database error, the statement is reset.
Resetting a statement[procedure] (reset statement)
Resets statement to the beginning of its program, returning the statement.
Finalizing a statement[procedure] (finalize statement)
Finalize statement. Finalizing a finalized statement or a cached statement is a no-op. Finalizing a statement on a closed database is also a no-op. Cached statements are finalized as they expire, and all other statements known to the SQLite library are automatically finalized when the database is closed, so it is rarely necessary to call this directly.
Transient statements (statements deliberately prepared to bypass the cache, including those that are prepared when cache size is zero) must be finalized either by using this procedure or the query / exec interface.[procedure] (resurrect statement)
Resurrects a previously finalized statement s or, if still alive, just resets it. Returns s, which is also modified in place.
Resurrection is accomplished either by pulling a previously prepared SQLite statement from the cache, or if it is not cached, by re-preparing the original SQL associated with the statement. Afterwards, the statement may be used normally.
Binding parameters[procedure] (bind statement index value)
Bind parameter at index of statement to value, and returns statement. The variable index may be an integer (the first parameter is 1, not 0) or a string for a named parameter --- for example, "$key", ":key" or "@key". For named parameters, the $, : or @ must be included in the string. A reference to an invalid index will throw an exception.[procedure] (bind-parameters statement . parameters)
Convenience function which binds parameters to indices 1 .. n, in order. Keyword arguments are permitted; foo: 3 will bind 3 to parameter :foo.
The number of parameters must match the statement's bind-parameter-count, or an error will be signaled. Also, all keywords used must be valid parameter names.
Mixing named and anonymous arguments in the same statement is not recommended.[procedure] (bind-parameter-count statement)
Returns the number of bound parameter slots in this prepared statement. If numbered parameters are present, gaps may be left in the sequence. Named parameters count in the slot total as well.[procedure] (bind-parameter-name statement i)
Returns a string representing the name of the bound parameter at index i, or #f if the parameter is anonymous or is out of range.
The string includes the parameter name prefix; for example ":foo", "$foo", "@foo" or "?nnn".
Obtaining result data
In this section's examples, we assume a simple database has been created with the following commands:
CREATE TABLE cache(key text, val text); INSERT INTO cache(key,val) VALUES('foo', 'bar'); INSERT INTO cache(key,val) VALUES('baz', 'quux');
and a SELECT statement has been prepared and stepped once:
(define s (prepare db "SELECT rowid, * from cache;")) (step s) ; => row
and s is implicitly reset between examples.[procedure] (column-name statement index)
Return the name of the specified result set column as a symbol. The statement need not have been stepped to retrieve column names or column count.
(column-name s 1) ; => key[procedure] (column-names statement)
Convenience function which returns a list of all column names for the result set, in order.
(column-names s) ; => (rowid key val)[procedure] (column-count statement)
Return the number of columns in the result set returned by the prepared statement.
(column-count s) ; => 3[procedure] (column-type statement index)
Returns the type of the indexed column in the current row. SQLite is dynamically typed and the column types are unique to each row.
(map (lambda (i) (column-type s i)) (list 0 1 2)) ; => (integer text text)[procedure] (column-data statement index)
Returns the data from the indexed column in the current row.
|Column type||Scheme type|
|integer||Exact or inexact number|
(map (lambda (i) (column-data s i)) (list 0 1 2)) ; => (1 "foo" "bar")
integer values are retrieved with sqlite3_column_int64. On a 32-bit machine, values outside the signed 31-bit fixnum range are returned as inexact numbers. On a 64-bit machine, values outside the signed 63-bit fixnum range are returned as inexact numbers. Note that inexact numbers are 64-bit floating point values, and can only accurately represent 53 bits of an integer.[procedure] (row-data statement)
Retrieve a list of column data from the current row. If the last execution of step returned done, a NULL value will be returned for every column.
(row-data s) ; => (1 "foo" "bar")[procedure] (row-alist statement)
Retrieve an alist mapping column names to column data for the current row.
(row-alist s) ; => ((rowid . 1) (key . "foo") (val . "bar"))[procedure] (change-count db)
Returns the number of database rows that were changed or inserted or deleted by the most recently completed SQL statement, not including triggers, as in sqlite3_changes.[procedure] (total-change-count db)
Returns the number of row changes caused by INSERT, UPDATE or DELETE statements since the database connection was opened, including triggers, as in sqlite3_total_changes.[procedure] (last-insert-rowid db)
Get the ROWID of the last successful INSERT, as in sqlite3_last_insert_rowid.
call-with-database[procedure] (call-with-database filename proc)
Opens a database, calls proc with the database object and then closes the database on return. If an error occurs in proc, the database is closed immediately.
Statements[procedure] (sql db sql-str)
Creates a statement object associated with the database connection db and the SQL sql-str. Preparation of the statement is deferred until needed. This is a normal statement in every respect except that it must be resurrected before it can be used.
sql is recommended over prepare when using the query / exec interface so that you can declare your statements without compiling them until and unless they are actually used.
Additionally, sql is safer. For example, when the statement cache is disabled, an error that occurs between prepare and query may leak an unfinalized statement. An error occurring between sql and query is no problem, because preparation is deferred until safely inside query. The same goes for sql/transient, which bypasses the cache completely.[procedure] (sql/transient db sql-str)
Equivalent to (sql db sql-str), but the statement will not be cached; it is prepared anew every time it is resurrected.
sql/transient is recommended over prepare-transient for the same reasons mentioned in sql.
Query[procedure] (query proc s . args)
Resurrects statement s, binds args to s using bind-parameters, and performs a query*. If the statement is transient, it is finalized immediately afterward, even if an exception occurs.
query is the usual way to perform a query unless you need to bind arguments manually, need more control or are using the low-level interface, in which case you can use query* if desired.
You typically call query or query* with one of the provided result fetching procedures; you can also pass your own procedure to perform whichever operations you would like.[procedure] (query* proc s)
Calls (proc s) and resets the statement s immediately afterward, to avoid locking the database. If an exception occurs during proc, the statement will still be reset. The statement is not reset before execution.
The entire purpose of query* is to ensure a statement is reset after it is executed. If a statement were left in a running state --- for example, if an uncaught exception occurs during proc, or you simply do not exhaust its result set --- then the database will be locked for writing until the statement is finalized.
Query procedures[procedure] (fetch s)
[procedure] (fetch-row s)
Fetch the next row of the result set. This is the equivalent to performing a step followed by a row-data call, and works with both the high- and low-level interfaces. If the statement has finished executing, fetch returns '(). These query procedures do not reset the statement before or afterward; one may do so using reset or query.
fetch and fetch-row are aliases.
(fetch s) ; => (1 "foo" "bar") (fetch s) ; => (2 "baz" "quux") (fetch s) ; => () (fetch s) ; => error (query fetch s) ; => (1 "foo" "bar") (query fetch s) ; => (1 "foo" "bar") (fetch s) ; => (1 "foo" "bar")[procedure] (fetch-all s)
[procedure] (fetch-rows s)
Calls fetch until it returns '(), and collects the result into a list. fetch-all and fetch-rows are aliases.
(query fetch-all s) ; => ((1 "foo" "bar") (2 "baz" "quux"))[procedure] (fetch-alist s)
Fetch the next row of the result set and return an alist mapping symbolic row names to values. Equivalent to step followed by row-alist.
(query fetch-alist s) ; ((rowid . 1) (key . "foo") (val . "bar"))[procedure] (fetch-alists s)
Fetches all rows and returns a list of alists, one per row.
(query fetch-alists s) ; (((rowid . 1) (key . "foo") (val . "bar")) ; ((rowid . 2) (key . "baz") (val . "quux")))[procedure] (fetch-value s)
Fetches and returns only the first value (first column) of the next row, or #f if the row contained no column data. Equivalent to using first-column on the result of a fetch, but does not materialize the entire row.
(query fetch-value (sql db "select key from cache")) ; => "foo"
(query fetch-value (sql db "select key from cache where key=?") "nosuchkey") ; => #f[procedure] (fetch-column s)
Fetches all rows and returns a list containing the first column of each, or '() if there was no column data.
(query fetch-column (sql db "select key from cache")) ; => ("foo" "bar")[procedure] (for-each-row proc)
[procedure] (for-each-row* proc)
Returns a procedure suitable for passing to query, taking one argument, a statement object.
The procedure will call fetch once for each row and call your callback as (proc row), discarding the results.
(query (for-each-row (lambda (x) (print "row: " x))) s) ; row: (1 foo bar) ; row: (2 baz quux) ; => undefined
for-each-row* behaves like for-each-row, but your callback is invoked with one argument for each column value. For example, these produce equivalent results:
(query (for-each-row (match-lambda ((name sql) (print "table: " name " sql: " sql ";")))) (sql db "select name, sql from sqlite_master;")) (query (for-each-row* (lambda (name sql) (print "table: " name " sql: " sql ";"))) (sql db "select name, sql from sqlite_master;"))[procedure] (map-rows proc)
[procedure] (map-rows* proc)
Return a procedure suitable for passing to query, taking one argument, a statement object.
The procedure will call fetch once for each row and call (proc row), collecting the results into a list, in order.
(query (map-rows car) s) ; => (1 2)
Another example; these two produce equivalent results:
(query (map-rows car) (sql db "select name, sql from sqlite_master;")) (map car (query fetch-all (sql db "select name, sql from sqlite_master;")))
map-rows* behaves like map-rows, but your callback is invoked with one argument for each column value.[procedure] (fold-rows kons knil)
[procedure] (fold-rows* kons knil)
Calls (kons x xs) once for each row, where x is the current row data and xs is the seed (previous return value from kons). The initial seed is knil.
(query (fold-rows cons '()) s) ; => ((2 "baz" "quux") (1 "foo" "bar"))
;; sum the returned rowids (query (fold-rows (lambda (x xs) (+ (car x) xs)) 0) s) ; => 3
;; that was contrived, you should actually do the sum in the database (car (query fetch (sql db "select sum(rowid) from mytable;"))) ; => 3
fold-rows* behaves like fold-rows, but the kons callback is invoked with one column for each argument value, plus the seed as the last argument -- for example, as (kons x y z seed). This turns out to be quite inefficient and makes little sense, so fold-rows* is deprecated as of 0.4.2.[procedure] (first-column row)
Returns the first column of row, or #f if the row is '().
(first-column (query fetch (sql db "select sum(rowid) from mytable;"))) ; => 3
You can also use fetch-value here instead:
(query fetch-value (sql db "select sum(rowid) from mytable;")) ; => 3
Execute[procedure] (exec s . args)
Resurrects statement s, binds args to s using bind-parameters, and performs an exec*. If s is transient, it is finalized immediately afterward, even if an exception occurs.[procedure] (exec* s)
Executes statement sql, returning the number of changes (if the result set has no columns as in INSERT, DELETE, UPDATE) or the first row (if column data is returned as in SELECT). In the latter case, it is like performing a (query* fetch s), but is more efficient.
Resurrection is omitted, as it would wipe out any bindings. Reset is NOT done beforehand; it is cheap, but the user must reset before a bind anyway.
The statement is always reset afterward, even if an exception occurs, to avoid locking the database. Note however that an internal error when retrieving column data (such as a string > 16MB) will leave the statement open -- this is a flaw in the current implementation.
(exec (sql db "INSERT INTO cache(key, val) values(?, ?);") "chicken" 4) ; => 1 (exec (sql db "SELECT * FROM cache WHERE key = ?;") "chicken") ; => ("chicken" "4") (first-column (exec (sql db "SELECT val FROM cache;"))) ; => "bar" (first-column (exec (sql db "SELECT val FROM cache;"))) ; => "bar"
with-transaction[procedure] (with-transaction db thunk #!optional (type deferred))
[procedure] (with-deferred-transaction db thunk)
[procedure] (with-immediate-transaction db thunk)
[procedure] (with-exclusive-transaction db thunk)
Executes thunk within a BEGIN TRANSACTION block, and returns the value of thunk. The optional type may be one of the symbols deferred, immediate, or exclusive. You may also use the named convenience functions instead of the optional parameter.
The transaction is committed with (commit db) if thunk returns a true value. Escaping or re-entering the dynamic extent of thunk will not commit or rollback the in-progress transaction. However, if an exception occurs during thunk, or thunk returns #f, or the commit fails, the transaction will be rolled back with (rollback db). If this rollback fails, that is a critical error and you should likely abort.
rollback[procedure] (rollback db)
Rollback current transaction. Unconditionally resets running queries before doing so, as rollback would fail if read or read/write queries are running. Successful rollback returns a true value. Rolling back in autocommit mode also returns a true value.
commit[procedure] (commit db)
Commit current transaction. This does not rollback running queries, because running read queries are acceptable, and the behavior in the presence of pending write statements is unclear. If the commit fails, you can always rollback, which will reset the pending queries.
Successful commit, or commit in autocommit mode, returns a true value.
autocommit?[procedure] (autocommit? db)
Returns #t if the database is in autocommit mode, or #f if within a transaction.
When a database error occurs, an exception of type (exn sqlite) is raised, containing the database error code and message. This information is also available from the database using the error-code and error-message interface.[procedure] (sqlite-exception? e)
Is e an exception raised by the database?[procedure] (sqlite-exception-status e)
Get the database error code as a symbol. See error-code for details.[procedure] (sqlite-exception-message e)
Get the database error message as a string.[procedure] (error-code db)
Returns the last database error code as a symbol.
|Symbol||C error code|
Returns the last database error message as a string.[parameter] (raise-database-errors BOOLEAN) [default: #t]
Set to #t to raise an exception on database error, #f to return a false value. Note that certain critical errors, such as "misuse of interface" and arity mismatches of bound parameters will raise exceptions regardless. Procedures in this extension that utilize the low-level interface are written to work correctly with both #f return values and errors.
Disabling raising of database errors is intended for experts and this option may be removed.
Busy handling is done outside of the library, instead of inside the library busy handler, because with SRFI-18 threads it is not legal to yield within a callback. The backoff algorithm of sqlite3_busy_timeout is reimplemented.
SQLite can deadlock in certain situations and to avoid this will return SQLITE_BUSY immediately rather than invoking the busy handler. However if there is no busy handler, we cannot tell a retryable SQLITE_BUSY from a deadlock one. To gain deadlock protection we register a simple busy handler which sets a flag indicating this BUSY is retryable. This is done without invoking a callback into Scheme.
set-busy-handler![procedure] (set-busy-handler! db proc)
Register the busy handler proc on the open connection db; the handler will be called repeatedly when a prepare or step operation returns SQLITE_BUSY. It is passed the two arguments (db count), which are the associated database connection and the number of times this busy handler has been invoked so far for this operation. The procedure should return #f to stop retrying and have the operation return a BUSY error to the caller, or #t if the busy operation should be retried.
By default, no busy handler is registered. Busy handlers are unique to each connection and must be registered after the connection is open.
(call-with-database (lambda (db) (set-busy-handler! db (busy-timeout 10000)) ; 10 second timeout ...))
busy-timeout[procedure] (busy-timeout ms)
Return a procedure suitable for use in set-busy-handler!, implementing a spinning busy timeout using the SQLite3 busy wait algorithm. This handler will wait up to ms milliseconds total before giving up. Other threads may be scheduled while this one is busy-waiting.
You may define your own scalar and aggregate functions in Scheme.
Currently, a significant performance penalty is imposed on all calls to step once the first user-defined function is registered, due to a limitation on callbacks in Chicken. This penalty is on the order of 10 times, and is imposed on all statements regardless of whether a user function is actually invoked. However, if no functions are registered, there is no penalty.[procedure] (register-scalar-function! db name nargs proc)
Register a user-defined scalar function name of arity nargs. nargs may range from 0 to 127, or -1 to define a function taking any number of arguments. You may define multiple functions with differing numbers of arguments. Defining a function with the same nargs as an existing function will redefine it, even built-in functions.
proc should be a function taking nargs arguments; to delete an existing function, set proc to #f. The return value is used as the value of the scalar function. If an error occurs during the function, it is signaled as a database error.
Functions must be defined anew for every database connection.
Be very careful when combining user-defined functions and SRFI-18 threads.[procedure] (register-aggregate-function! db name nargs pstep #!optional (seed 0) (pfinal identity))
Register a user-defined aggregate function name of arity nargs. nargs may range from 0 to 127, or -1 to define a function taking any number of arguments. You may define multiple functions with differing numbers of arguments. Defining a function with the same nargs as an existing function will redefine it, even built-in functions.
seed is the initial seed passed to this particular invocation of the aggregate function. At every step, pstep is invoked as (pstep seed arg1 ... argn) and its return value becomes the next seed. Finally, (pfinal seed) is invoked to do any final transformation necessary on the seed. (For example, if seed is a record, you may need to pull out and return the relevant data.) The return value of pfinal is used as the value of the aggregate function. If an error occurs during pstep or pfinal, it is signaled as a database error.
pstep should be a function taking nargs arguments. To delete an existing aggregate function, set pstep to #f. In this case the values of seed and pfinal are ignored.
Functions must be defined anew for every database connection.
Be very careful when combining user-defined functions and SRFI-18 threads.
Callbacks and SRFI-18
Warning. Callbacks are inherently unsafe in combination with SRFI-18 threads; callbacks must always be exited in the order they were entered, which can be violated with thread-switching or call/cc. sql-de-lite takes care to disable thread scheduling inside user-defined function callbacks. It also traps and safely signals errors via the library.
However, you must not:
- invoke call/cc to escape the user-defined function
- invoke thread-yield! or thread-sleep!
- perform blocking I/O (for example, writing to a file or network port)
unless you are a wizard, or can guarantee no other thread can ever invoke a callback (even one created with another egg).
User-defined functions have not been heavily stress-tested in the presence of multiple threads, so caution is advised.
Miscellaneous[procedure] (schema db)
Returns a list of SQL statements making up the database schema.[procedure] (print-schema db)
Displays the database schema to the current output port; the result is similar to using .schema at the sqlite3 command prompt.[procedure] (flush-cache! db)
Flush the prepared statement cache,[procedure] (finalized? statement)
Returns #t if the statement is finalized or has never been prepared.
(finalized? (sql db "select 1;")) ; => #t (finalized? (prepare db "select 1;")) ; => #f[string] library-version
A string representing the SQLite3 library version (e.g. "3.6.11").
If you are operating on the same database in multiple threads, you must open a new connection per thread. Reusing the same connection will result in corruption.
Be very careful when combining user-defined functions and SRFI-18 threads.
About this egg
- Reverse seed and pstep args to register-aggregate-function!, make seed optional
- Scalar and aggregate user-defined functions. Upgrade internal library to 3.7.11.
- Support named parameters.
- Add database-closed?, sql/transient. Ensure transient statements are finalized in QUERY and EXEC. Disable last-resort finalization of open statements in close-database. Warn if database is not closed after call-with-database. Ensure statement column count and column names are correct if the database schema changes. Make preparing whitespace/comment SQL illegal (for now). Ensure resurrected transient statements are still transient.
- Add fetch-value, -column, -alists, -row, and -rows. Reset execed stmts that return 0 rows, preventing spurious reserved lock after ROLLBACK. Bind exact numbers to int64, not int.
- Remove deprecated milliseconds->time call
- byte-vector and pointer types upgraded for compat with Chicken 4.7
- Upgrade to SQLite 3.7.3; fix fold-rows* (and deprecate it)
- Drop dependency on easyffi
- Add integrated SQLite3 library
- Initial release
The egg is BSD-licensed. The SQLite 3 library is public domain.